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Most C preprocessor features are inactive unless you give specific directives to request their use.
´ëºÎºÐÀÇ C Àü󸮱â´Â ±×°ÍµéÀÇ »ç¿ëÀ» ¿äûÇϴ ƯÁ¤ Áö½Ã¹®À» ÁÖÁö ¾Ê´Â ÇÑ È°µ¿ÇÏÁö ¾Ê´Â´Ù.
(Preprocessing directives are lines starting with a `#' token, possibly preceded by whitespace; see section Preprocessing Directives).
(Àüó¸® Áö½Ã¹®µéÀº ¶óÀΠóÀ½¿¡ `#' ÅäÅ«À¸·Î ½ÃÀÛÇÑ´Ù. °ø¹éÀÌ ¿À´Â °Íµµ °¡´ÉÇÏ´Ù.)
However, there are four transformations that the preprocessor always makes on all the input it receives, even in the absence of directives. These are, in order:
±×·¯³ª Áö½Ã¹®ÀÌ ¾ø¾îµµ ¸ðµç ÀÔ·ÂÀ» Àü󸮱Ⱑ ó¸®ÇÏ´Â ³× °¡Áö º¯ÇüµÈ ¸ð¾çÀÌ ÀÖ´Ù.
For end-of-line indicators, any of \n, \r\n, \n\r and \r are recognised, and treated as ending a single line. As a result, if you mix these in a single file you might get incorrect line numbering, because the preprocessor would interpret the two-character versions as ending just one line. Previous implementations would only handle UNIX-style \n correctly, so DOS-style \r\n would need to be passed through a filter first.
end-of-line Áö½Ã¹®À» À§ÇØ, \n, \r\n, \n\r ±×¸®°í \r ÀÌ ÀÎÁ¤ µÇ°í ÇÑ ¶óÀÎÀÇ ³¡À¸·Î½á ´Ù·ç¾îÁø´Ù. Àü󸮱â´Â ¶óÀÎÀÇ ³¡À¸·Î½á µÎ °¡Áö ¹®ÀÚ ¹öÀüÀ»0 Çؼ®Çϱ⠶§¹®¿¡, ¸¸¾à À̰͵éÀ» ¼¯¾î ¾´ ´Ù¸é, ºÎÁ¤È®ÇÑ ¶óÀÎ ¼ö¸¦ ¾ò°Ô µÉ °ÍÀÌ´Ù. ÀÌÀü¿¡´Â Á¤È®ÇÏ°Ô À¯´Ð½º ½ºÅ¸ÀÏÀÎ \n¸¸À» ´Ù·ç¾ú´Ù. ±×·¡¼ DOS DOS-style \r\nÀº óÀ½¿¡ ÇÊÅÍ·Î °É·¯Áö´Â °ÍÀÌ ÇÊ¿äÇß´Ù.
The first three transformations are done before all other parsing and before preprocessing directives are recognized. Thus, for example, you can split a line mechanically with backslash-newline anywhere (except within trigraphs since they are replaced first; see below).
óÀ½ »õ °¡ÁöÀÇ º¯ÇüÀº ¸ðµÎ ´Ù¸¥ ¾î±¸ÀÇ parsing°ú Áö½Ã¹®µéÀ» ¹Ì¸® Á¶»ç·ºÐ¼®ÇÏ´Â °ÍÀÌ ÀνĵDZâ Àü¿¡ ¼öÇàµÈ´Ù.°Ô´Ù°¡ ,¿¹¸¦ µé¸é, ´ç½ÅÀº ¾îµðµçÁö backslash-newline·Î ±â°èÀûÀ¸·Î ¶óÀÎÀ» ³ª´ ¼ö ÀÖ´Ù..
/* */ # /* */ defi\ ne FO\ O 10\ 20
is equivalent into `#define FOO 1020'.
There is no way to prevent a backslash at the end of a line from being interpreted as a backslash-newline. For example,
backslash-newline·Î Çؼ®µÇ´Â ¶óÀÎÀÇ ³¡¿¡ ¹é½½·¡½Ã¸¦ ¸·À» ÇÊ¿ä´Â ¾ø´Ù..¿¹¸¦ µé¸é,
"foo\\ bar"
is equivalent to "foo\bar"
, not to "foo\\bar"
. To avoid
having to worry about this, do not use the GNU extension which permits
multi-line strings. Instead, use string constant concatenation:
foo\\bar°¡ ¾Æ´Ï¶ó foo\bar¿Í °°´Ù.ÀÌ°Í¿¡ ´ëÇÑ °ÆÁ¤À» ÇÇÇϱâ À§ÇØ multi-line¿¡ ½ºÆ®¸µÀ» °¡´ÉÄÉ ÇÑ GNU È®ÀåÀ» »ç¿ëÇÏÁö ¸¶¶ó.´ë½Å¿¡, ½ºÆ®¸µ »ó¼ö ¿¬°áÀ» »ç¿ëÇϽÿÀ.
"foo\\" "bar"
Your program will be more portable this way, too.
´ç½ÅÀÇ ÇÁ·Î±×·¥Àº ÀÌ·± ¹æ¹ý¿¡ ¶ÇÇÑ ´õ °¡¿ëÀûÀÏ °ÍÀÌ´Ù.
There are a few things to note about the above four transformations.
³× °¡Áö º¯Çü¿¡ ´ëÇØ ÁÖÀÇ ÇØ¾ß ÇÒ ¸î °¡Áö°¡ ÀÖ´Ù.
The preprocessor handles null characters embedded in the input file depending upon the context in which the null appears. Note that here we are referring not to the two-character escape sequence "\0", but to the single character ASCII NUL.
Àü󸮱â´Â null¹®ÀÚµéÀ» nullÀÌ ³ªÅ¸³ª´Â ¹®¸ÆÀ» °®´Â ÀÔ·Â ÆÄÀϵ鿡 ³¢¿ö ³Ö´Â´Ù. ¿©±â¿¡ ¿ì¸®µéÀÌ two-character Å»Ãâ ·Î" \0 "°¡ ¾Æ´Ï¶ó ÇϳªÀÇ ¾Æ½ºÅ° NUL·Î »ý°¢ÇÏ´Â °Í¿¡ ÁÖÀÇ Ç϶ó..
There are three different contexts in which a null character may appear:
null ¹®ÀÚ°¡ ³ªÅ¸³¯ ¸¸ÇÑ ¼¼°¡Áö ´Ù¸¥ ¹®¸ÆÀÌ ÀÖ´Ù.
#define X^@1is equivalent to
´Â ¾Æ·¡¿Í °°´Ù
#define X 1and X is defined with replacement text "1".
±×¸®°í X´Â 1·Î ´ëüµÇ´Â °ÍÀ¸·Î Á¤ÀÇ µÈ´Ù.
Most preprocessor features are active only if you use preprocessing directives to request their use.
´ëºÎºÐÀÇ Àü󸮱â´Â »ç¿ëÇϱâ À§ÇØ Àüó¸® Áö½Ã¹®À» »ç¿ëÇؾ߸¸ È°¼ºÈ µÈ´Ù.
Preprocessing directives are lines in your program that start with `#'. Whitespace is allowed before and after the `#'. The `#' is followed by an identifier that is the directive name. For example, `#define' is the directive that defines a macro.
Àüó¸® Áö½Ã¹®Àº `#'°ú ÇÔ²² ÇÁ·Î±×·¥ ¶óÀο¡ ÀÖ´Ù. `#' µÚ¿Í Àü¿¡ °ø¹éÀº Çã¶ôµÈ´Ù. `#' µÚ¿¡´Â Á÷Á¢ÀûÀÎ À̸§ ½Äº°ÀÚ°¡ µû¸¥´Ù. ¿¹¸¦ µé¾î `#define'Àº ¸ÅÅ©·Î¸¦ Á¤ÀÇ ÇÏ´Â °ÍÀ» Áö½Ã ÇÑ´Ù.
Since the `#' must be the first token on the line, it cannot come from a macro expansion if you wish it to begin a directive. Also, the directive name is not macro expanded. Thus, if `foo' is defined as a macro expanding to `define', that does not make `#foo' a valid preprocessing directive.
`#'ÀÌ ¶óÀο¡ ù¹ø° ÅäÅ«ÀÌ µÇ¾î¾ß Çϱ⠶§¹®¿¡, ¸¸¾à Áö½Ã¹®À» ½ÃÀÛÇϱ⸦ ¹Ù¶ó¸é ±×°ÍÀº ¸ÅÅ©·Î È®ÀåºÎÅÍ ¿Ã ¼ö ¾ø´Ù.¶ÇÇÑ, Áö½Ã¹® À̸§Àº È®ÀåµÈ ¸ÅÅ©·Î°¡ ¾Æ´Ï´Ù. ÀÌó·³ `foo'´Â `define'¿¡¼ È®ÀåµÈ ¸ÅÅ©·Î·Î¼ Á¤ÀÇ µÇ¸é, `#foo'´Â Á¤´çÇÑ Àüó¸® Áö½Ã¹®ÀÌ ¾Æ´Ï´Ù.
The set of valid directive names is fixed. Programs cannot define new preprocessing directives.
È®½ÇÇÑ ±Ù°Å°¡ ÀÖ´Â Áö½Ã¹® À̸§µéÀÇ set´Â °íÁ¤µÈ´Ù. ÇÁ·Î±×·¥µéÀº »õ·Î¿î Àüó¸® Áö½Ã¹®µéÀ» Á¤ÀÇ ÇÒ ¼ö ¾ø´Ù.
Some directive names require arguments; these make up the rest of the directive line and must be separated from the directive name by whitespace. For example, `#define' must be followed by a macro name and the intended expansion of the macro. See section Object-like Macros.
¸î¸î Áö½Ã¹® À̸§µéÀº ÀÎÀÚµéÀ» ¿ä±¸ÇÑ´Ù; À̰͵éÀº Áö½Ã¹® ¶óÀÎÀÇ ³ª¸ÓÁö¸¦ ¸¸µé°í °ø¹é¿¡ ÀÇÇؼ Áö½Ã¹® À̸§À¸·ÎºÎÅÍ ºÐ¸®µÇ¾î¾ß ÇÑ´Ù.¿¹¸¦ µé¸é, '#define'´Â ¸ÅÅ©°í À̸§ÀÌ°í ¸ÅÅ©·Î¿¡¼ ÀǵµµÈ È®ÀåÀÌ µÚµû¶ó¾ß ÇÑ´Ù. Object-like Macros.ºÎºÐÀ» ºÁ¶ó
A preprocessing directive cannot cover more than one line. It may be logically extended with backslash-newline, but that has no effect on its meaning. Comments containing newlines can also divide the directive into multiple lines, but a comment is replaced by a single space before the directive is interpreted.
Àüó¸® Áö½Ã¹®Àº ÇÑ ¶óÀκ¸´Ù ¸¹À» ¼ö ¾ø´Ù.±×°ÍÀº ³í¸®ÀûÀ¸·Îbackslash-newline·Î È®ÀåµÉÁöµµ ¸ð¸£Áö¸¸, ±×°ÍÀÇ Àǹ̴ ¾Æ¹« ¿µÇâÀ» ³¢Ä¡Áö ¾Ê´Â´Ù.. newlines¸¦ ´ã°í ÀÖ´Â ÁÖ¼®Àº ¶ÇÇÑ ¿©·¯ °³ ¶óÀÎÀ¸·Î Áö½Ã¹®À» ³ª´ ¼ö ÀÖÁö¸¸ ÁÖ¼®Àº Áö½Ã¹®ÀÌ Çؼ®µÇ±â Àü¿¡ ÇÑ °ø°£À¸·Î ¹Ù²ï´Ù.
A header file is a file containing C declarations and macro definitions (see section Macros) to be shared between several source files. You request the use of a header file in your program with the C preprocessing directive `#include'.
Çì´õ ÆÄÀÏÀº ¸î¸î ¼Ò½º ÆÄÀϵé»çÀÌ¿¡ °øÀ¯µÇ±â À§ÇÏ¿© C ¼±¾ðµé ±×¸®°í ¸ÅÅ©·Î Á¤ÀÇ(Ž»ö ¼½¼Ç Macros)¸¦ Æ÷ÇÔÇÑ ÆÄÀÏÀÌ´Ù. ´ç½ÅÀº `#include' CÀü󸮱â·Î Çì´õÆÄÀÏ »ç¿ëÀ» ¿äûÇÑ´Ù.
Header files serve two kinds of purposes.
Çì´õ ÆÄÀϵéÀº µÎ°¡Áö ¸ñÀûÀ¸·Î Á¦°øµÈ´Ù.
Including a header file produces the same results in C compilation as copying the header file into each source file that needs it. Such copying would be time-consuming and error-prone. With a header file, the related declarations appear in only one place. If they need to be changed, they can be changed in one place, and programs that include the header file will automatically use the new version when next recompiled. The header file eliminates the labor of finding and changing all the copies as well as the risk that a failure to find one copy will result in inconsistencies within a program.
°¢ ¼Ò½º ÆÄÀÏ·Î Çì´õ ÆÄÀÏÀ» º¹»çÇÏ´Â °Í°ú Çì´õÆÄÀÏÀ» Æ÷ÇÔ½ÃÅ°´Â °ÍÀº C ÄÄÆÄÀÏ¿¡¼ °°Àº °á°ú¸¦ ¸¸µç´Ù. ±×¿Í °°ÀÌ º¹»ç´Â ½Ã°£À» ³¶ºñÇÒ °ÍÀÌ°í error-proneÀÏ °ÍÀÌ´Ù. Çì´õ ÆÄÀÏ¿¡¼, °ü°è°¡ ÀÖ´Â ¼±¾ðµéÀº ´ÜÁö ÇϳªÀÇ Àå¼Ò¿¡ ³ªÅ¸³´Ù. ¸¸¾à ±×°ÍÀÇ ¼öÁ¤ÀÌ ÇÊ¿ä ÇÏ´Ù¸é, ÇÑ °÷¿¡¼ ¼öÁ¤ ÇÒ ¼ö ÀÖ°í ÀÚµ¿ÀûÀ¸·Î Çì´õ ÆÄÀÏÀ» Æ÷ÇÔÇÑ ÇÁ·Î±×·¥µéÀº ´ÙÀ½¿¡ ´Ù½Ã ÄÄÆÄÀÏÀ» ÇÒ ¶§ »õ·Î¿î ¹öÀüÀ» »ç¿ëÇÑ´Ù. Çì´õ ÆÄÀÏÀº ÄÚµå º¹»ç·Î ÀÎÇÑ ÇÁ·Î±×·¥ ³»¿¡¼ÀÇ ºÒÀÏÄ¡¸¦ ãÁö ¸øÇÏ´Â À§Çè»Ó¸¸ ¾Æ´Ï¶ó ¸ðµç ¹®¼µéÀ» ã¾Æ³»°í ¼öÁ¤ÇØ¾ß ÇÏ´Â ³ëµ¿À» ¾ø¾Ö ÁØ´Ù.,
The usual convention is to give header files names that end with `.h'. Avoid unusual characters in header file names, as they reduce portability.
ÀϹÝÀûÀÎ ±ÔÁ¤Àº Çì´õ ÆÄÀϵé À̸§µéÀÇ ³¡À» ' .h' ÇÏ´Â °ÍÀÌ´Ù. ¹®ÀÚ°¡ ÀÖ´Â Çì´õ ÆÄÀÏ À̸§µé¿¡ ÀÌ»óÇÑ ¹®ÀÚµéÀ» ÇÇÇ϶ó!. ±×µéÀº °¡¿ë¼ºÀ» °ÝÇϽÃŲ´Ù.
Both user and system header files are included using the preprocessing directive `#include'. It has three variants:
»ç¿ëÀÚ¿Í ½Ã½ºÅÛ Çì´õ ÆÄÀÏµé ¸ðµÎ '#include' Àü󸮱⸦ ÀÌ¿ëÇؼ Æ÷ÇÔ½ÃŲ´Ù. ¼¼°¡Áö º¯ÇüÀÌ ÀÖ´Ù.
#include <file>
ÀÌ º¯ÇüÀº ½Ã½ºÅÛ Çì´õ ÆÄÀϵ鿡 ¾´´Ù. fileÀ̶õ À̸§ÀÇ ÆÄÀÏÀº ´ç½ÅÀÇ Æ¯º°ÇÑ µð·ºÅ丮¿¡ ¸®½ºÆ®¿¡¼ ãÀº ´ÙÀ½ ÀϹÝÀûÀÎ ½Ã½ºÅÛ µð·ºÅ丮¿¡¼ ã´Â´Ù. ´ç½ÅÀº ¸í·É ¿É¼Ç `-I'·Î ÇØ´õÆÄÀϵéÀ» ã±â À§ÇÑ µð·ºÅ丮¸¦ ¸í½Ã ÇÒ ¼ö ÀÖ´Ù. `-nostdinc' ¿É¼ÇÀº ÀϹÝÀûÀÎ ½Ã½ºÅÛ µð·ºÅ丮µéÀ» °Ë»öÇÏ´Â °ÍÀ» ¹æÁöÇÑ´Ù; ÀÌ °æ¿ì ´ç½ÅÀÌ ¸í½ÃÇÑ µð·ºÅ丮µé¿¡¼¸¸ °Ë»öÇÑ´Ù.
#include "file"
ÀÌ º¯ÇüÀº ´ç½Å ÀÚ½ÅÀÇ ÇÁ·Î±×·¥ÀÇ Çì´õ ÆÄÀϵéÀ» À§Çؼ »ç¿ëµÈ´Ù. ÆÄÀÏÀÌ fileÀ̶ó°í ºÒ¸®¾ú±â ÇöÀç µð·ºÅ丮°¡ ¸ÕÀú Ž»öµÇ°í ±× ´ÙÀ½¿¡ ½Ã½ºÅÛ Çì´õ ÆÄÀϵéÀ» À§Çؼ »ç¿ëµÇ´Â µð·ºÅ丮µéÀ» Ž»öÇÑ´Ù. ÇöÀç µð·ºÅ丮´Â ÇöÀç ÀÔ·Â ÆÄÀÏÀÇ µð·ºÅ丮ÀÌ´Ù. ÇöÀç ÀÔ·ÂÆÄÀÏ·Î ¿©°ÜÁö´Â ÆÄÀÏÀÇ À§Ä¡·Î °¡Á¤ µÇ±â ¶§¹®¿¡ ¸ÕÀú ½Ãµµ µÈ´Ù.( ¸¸¾à £I- ¿É¼ÇÀÌ »ç¿ëµÈ´Ù¸é, ÇöÀç µð·ºÅ丮ÀÇ Æ¯º°ÇÑ Ã³¸®°¡ ±ÝÁöµÈ´Ù. Invoking the C Preprocessor¸¦ ºÁ¶ó)
¸ÕÀú ` " '¹®ÀÚ´Â ÆÄÀÏ À̸§À» ³¡À» ³ªÅ¸³½´Ù. ÀÌ·± µÎ º¯Çüµé¿¡¼, ÀÎÀÚ´Â ÁÖ¼®¿¡¼ ¹®ÀÚ¿ »ó¼ö°¡ ÀνĵÇÁö ¾Ê´Â °Íó·³ Çൿ ÇÑ´Ù.
°Ô´Ù°¡' #include<x /* y> ' ¿¡¼ /* Àº ÁÖ¼®À» ½ÃÀÛÀ» ³ªÅ¸³»Áö ¾Ê°í ' x /* y'·Î ºÒ·ÁÁö´Â Çì´õÆÄÀÏ À̸§À» ³»Æ÷ÇÏ´Â Áö½Ã¹®À¸·Î ±¸Ã¼ÈµÈ´Ù. .
±×·¯³ª, ¸¸¾à ¹é½½·¡½ÃµéÀÌ ÆÄÀÏÀÇ ¾ÈÂÊ¿¡ ³ªÅ¸³ª¸é ¾î´À º¯Çü¿¡¼µµ, ±×µéÀº È®Àå ¹®ÀÚµéÀÌ ¾Æ´Ï¶ó Åë»ó ÅؽºÆ® ¹®ÀÚµé·Î »ý°¢µÈ´Ù. C¿¡ Å»Ãâ ¹®ÀÚ»ó¼ö·Î ÀûÇÕÇÑ °ÍÀÌ ¾ø´Ù. ÀÌó·³, 3°³ÀÇ ¹é½½·¡½Ã¸¦ ´ã°í ÀÖ´Â ÆÄÀÏ À̸§À» ' #include " x\n\\y " '·Î ÁöÁ¤ÇÑ´Ù.
#include anything else
ÀÌ º¯ÇüÀº °è»êµÈ #include·Î ºÒ¸°´Ù. ÀÎÀÚ°¡ À§ÀÇ2°¡Áö ÀÎÀÚ Çü½Ä¿¡ ¸ÂÁö ¾Ê´Â ¾î¶°ÇÑ '#include' Áö½Ã¹®µµ °è»êµÈ includeÀÌ´Ù. ÅؽºÆ® ±×¹Û¿¡ ¹«¾ùÀ̵çÁö ¸ÅÅ©·Î È£ÃâÀ» À§ÇØ È®ÀεȴÙ. ±× È£ÃâÀº È®ÀåµÈ´Ù.( see section Macros). ÀÌ°ÍÀÌ ¾²¿©Áú ¶§ °á°ú´Â ƯÈ÷ À§¿¡ 2°¡ÁöÀÇ º¯ÇüÁßÀÇ Çϳª¿Í ¾î¿ï·Á¾ß ÇÑ´Ù. - ƯÈ÷, È®ÀåÀº ¹®ÀÚ¿ »ó¼ö ¡ǥ¸¦ Çü¼º½ÃÅ°°Å³ª, ¶Ç´Â angle braces·Î µÑ·¯½ÎÀÎ ÅäÅ«µéÀÇ ¿·Î Çü¼ºÇØ¾ß ÇÑ´Ù. See section Implementation-defined Behavior and Implementation Limits. ÀÌ Æ¯Â¡Àº ´ç½ÅÀÌ ÇÁ·Î±×·¥¿¡¼ Á¶±Ý ´õ ´Ê°Ô »ç¿ëµÈ ÆÄÀÏ À̸§À» Á¦¾îÇÏ´Â ¸ÅÅ©·Î¸¦ ±ÔÁ¤Çϵµ·Ï Çã¿ëÇÑ´Ù.
ÀÌ·± ¾ÖÇø®ÄÉÀ̼ÇÀº ´ç½Å ÇÁ·Î±×·¥ÀÌ »ç¿ëµÈ ÆÄÀϵéÀ» Æ÷ÇÔÇÏ´Â ½Ã½ºÅÛÀÇ À̸§À» ÁöÁ¤Çϵµ·Ï site-specific configurationÆÄÀÏÀ» Çã¿ëÇÑ´Ù. ÀÌ°ÍÀº ´Ù¸¥ Àå¼Òµé¿¡¼ ÇÊ¿äÇÑ ½Ã½ºÅÛ Çì´õ ÆÄÀϵéÀ» ã´Â ¿©·¯ °¡Áö ¿î¿µÃ¼Á¦¿¡ ÇÁ·Î±×·¥ À̽ÄÀ» µµ¿ï ¼ö ÀÖ´Ù.
The `#include' directive works by directing the C preprocessor to scan the specified file as input before continuing with the rest of the current file. The output from the preprocessor contains the output already generated, followed by the output resulting from the included file, followed by the output that comes from the text after the `#include' directive. For example, given a header file `header.h' as follows,
#include Áö½Ã¹®Àº ÇöÀç ÆÄÀÏÀÇ ¿©ºÐÀ¸·Î °è¼Ó µÇ±â Àü¿¡ ÀÔ·ÂÀ¸·Î½á ƯÁ¤ÇÑ ÆÄÀÏÀ» °Ë»öÇÏ´Â C Àü󸮱⸦ °ü¸®ÇÏ´Â °Í¿¡ ÀÇÇØ ÀÛµ¿ÇÑ´Ù. Àü󸮱â·Î¿¡ Ãâ·ÂÀº includeµÈ ÆÄÀÏ¿¡¼ Ãâ·ÂÀÇ °á°ú (#include Áö½Ã¹® ÈÄ¿¡ ÅؽºÆ®·ÎºÎÅÍ ÀÏ¾î³ Ãâ·Â¿¡ ÀÇÇؼ)¿¡ µû¶ó ÀÌ¹Ì ¸¸µé¾îÁø Ãâ·ÂÀ» °®´Â´Ù. ¿¹¸¦ µé¸é, ´ÙÀ½°ú °°ÀÌ Çì´õ ÆÄÀÏ 'header.h'À» ÁÖ¾îÁý´Ï´Ù, .
char *test ();
and a main program called `program.c' that uses the header file, like this,
±×¸®°í mainÇÁ·Î±×·¥Àº ¾Æ·¡¿Í °°Àº ÇØ´õ ÆÄÀÏÀ» »ç¿ëÇÏ´Â `program.c' ÀÌ´Ù
int x; #include "header.h" main () { printf (test ()); }
the output generated by the C preprocessor for `program.c' as input would be
int x; char *test (); main () { printf (test ()); }
Included files are not limited to declarations and macro definitions; those are merely the typical uses. Any fragment of a C program can be included from another file. The include file could even contain the beginning of a statement that is concluded in the containing file, or the end of a statement that was started in the including file. However, a comment or a string or character constant may not start in the included file and finish in the including file. An unterminated comment, string constant or character constant in an included file is considered to end (with an error message) at the end of the file.
Æ÷ÇÔµÈ ÆÄÀϵéÀº ¼±¾ðµé ±×¸®°í ¸ÅÅ©·Î Á¤ÀÇ¿¡ Á¦ÇѵÇÁö ¾Ê´Â´Ù; Àú°ÍµéÀº ´ÜÁö ÀüÇüÀûÀÎ »ç¿ëÀÌ´Ù. C ÇÁ·Î±×·¥ÀÇ ¾î¶°ÇÑ fragment¶óµµ ¶Ç ´Ù¸¥ ÆÄÀϷκÎÅÍ include µÉ ¼ö ÀÖ´Ù. includeÆÄÀÏÀº ´ã°í ÀÖ´Â ÆÄÀÏ¿¡ °á¸» ºÎÀÇ ½ÃÀÛ ¶Ç´Â includingÆÄÀÏÀÇ ½ÃÀÛ ³¡¿¡ Æ÷ÇÔ µÉ ¼ö ÀÖ´Ù. ±×·¯³ª ÁÖ¼®À̳ª ¹®ÀÚ¿ ¶Ç´Â ¹®ÀÚ »ó¼ö´Â including ÆÄÀÏÀÇ ½ÃÀÛÀ̳ª ³¡ÀÌ ¾Æ´Ò °ÍÀÌ´Ù. including ÆÄÀÏ¿¡ ¸¶ÃÄÁöÁö ¾ÊÀº ÁÖ¼®, ¹®ÀÚ¿ »ó¼ö, ¹®ÀÚ »ó¼ö´Â (¿¡·¯ ¸Þ½ÃÁö¿Í ÇÔ²²) ÆÄÀÏÀÇ ³¡¿¡ ³¡À¸·Î »ý°¢µÇ¾î Áø´Ù.
It is possible for a header file to begin or end a syntactic unit such as a function definition, but that would be very confusing, so don't do it.
Çì´õ ÆÄÀÏÀº ÇÔ¼ö Á¤ÀÇ¿Í °°Àº ±¸¹®ÀûÀÎ ÀåÄ¡¸¦ ½ÃÀÛÇϰųª ³¡³»´Â °ÍÀº °¡´ÉÇÏÁö¸¸ ±×°ÍÀº ¸Å¿ì È¥¶õ½º·¯¿ï °ÍÀÌ´Ù. ±×·¡¼ ±×·¸°Ô ÇÏÁö ¾Ê´Â´Ù.
The line following the `#include' directive is always treated as a separate line by the C preprocessor, even if the included file lacks a final newline.
`#include' Áö½Ã¹® ´ÙÀ½¿¡ ¶óÀÎÀº includedµÈ ÆÄÀÏ¿¡ ¸¶Áö¸· newlineÀÌ ºÎÁ· Çصµ Ç×»ó C Àü󸮱⿡ ÀÇÇØ ºÐ¸®µÈ ¶óÀÎÀ¸·Î½á ´Ù·ç¾î Áø´Ù.
Very often, one header file includes another. It can easily result that a certain header file is included more than once. This may lead to errors, if the header file defines structure types or typedefs, and is certainly wasteful. Therefore, we often wish to prevent multiple inclusion of a header file.
¸Å¿ì ÀÚÁÖ, 1°³ÀÇ Çì´õ ÆÄÀÏÀº ´Ù¸¥ Çì´õ ÆÄÀÏÀ» Æ÷ÇÔÇÑ´Ù.¾î¶² Çì´õ ÆÄÀÏÀÌ ¿©·¯ ¹ø¿¡ °ÉÃÄ Æ÷ÇԵǴ °ÍÀº ½±°Ô ¹ß»ý ÇÒ ¼ö ÀÖ´Ù. ¸¸¾à Çì´õ ÆÄÀÏÀÌ ±¸Á¶ Çüµé ¶Ç´Â typedefs¸¦ ±ÔÁ¤Çϸé ÀÌ°ÍÀº ¿¡·¯¸¦ ÃÊ·¡ÇÏ°í ºñ°æÁ¦ÀûÀÌ´Ù.±×·¯¹Ç·Î, ¿ì¸®µé ÀÚÁÖ Çì´õ ÆÄÀÏÀÇ ´ÙÁß ³»Æ÷¸¦ ¸·´Â °ÍÀ» ¿øÇÑ´Ù.
The standard way to do this is to enclose the entire real contents of the file in a conditional, like this:
ÀÌ°ÍÀ» ÇÒ Ç¥ÁØ ¹æ¹ýÀº ÀÌ°Íó·³ Á¶°Ç¾î±¸¿¡ ÆÄÀÏÀÇ Àüü ½ÇÁ¦³»¿ëµéÀ» µÑ·¯½Î´Â °ÍÀÌ´Ù:
#ifndef FILE_FOO_SEEN #define FILE_FOO_SEEN the entire file #endif /* FILE_FOO_SEEN */
The macro FILE_FOO_SEEN
indicates that the file has been included
once already. In a user header file, the macro name should not begin
with `_'. In a system header file, this name should begin with
`__' to avoid conflicts with user programs. In any kind of header
file, the macro name should contain the name of the file and some
additional text, to avoid conflicts with other header files.
¸ÅÅ©·Î FILE_FOO_SEENÀº ÆÄÀÏÀÌ ÇÑ ¹ø ÀÌ¹Ì Æ÷ÇԵǾú´ø °ÍÀ» ³ªÅ¸³½´Ù.»ç¿ëÀÚ Çì´õ ÆÄÀÏ¿¡, ¸ÅÅ©·Î À̸§Àº ' _'·Î ½ÃÀÛÇÏÁö ¾Ê¾Æ¾ß ÇÑ´Ù. ½Ã½ºÅÛ Çì´õ ÆÄÀÏ¿¡, ÀÌ À̸§Àº »ç¿ëÀÚ ÇÁ·Î±×·¥µé°ú Ãæµ¹µéÀ» ÇÇÇϱâ À§ÇÏ¿© '__'À» °¡Áö°í ½ÃÀÛÇÏ¿©¾ß¸¸ ÇÑ´Ù. ¾î¶² Á¾·ùÀÇ Çì´õÆÄÀÏ¿¡¼, ¸ÅÅ©°í À̸§Àº ´Ù¸¥ Çì´õ ÆÄÀϵé°ú Ãæµ¹µéÀ» ÇÇÇϱâ À§ÇÏ¿© ÆÄÀÏ°ú ¸î¸î Ãß°¡ÀûÀÎ ÅؽºÆ®ÀÇ À̸§À» Æ÷ÇÔÇÏ¿©¾ß¸¸ ÇÑ´Ù.
The GNU C preprocessor is programmed to notice when a header file uses this particular construct and handle it efficiently. If a header file is contained entirely in a `#ifndef' conditional, modulo whitespace and comments, then it remembers that fact. If a subsequent `#include' specifies the same file, and the macro in the `#ifndef' is already defined, then the directive is skipped without processing the specified file at all.
Çì´õ ÆÄÀÏÀÌ Æ¯º°ÇÑ ±¸Á¶¸¦ »ç¿ëÇÏ°í ±×°ÍÀ» È¿À²ÀûÀ» ´Ù·ê ¶§¸¦ ¾Ë ¼ö ÀÖµµ·Ï GNU C Àü󸮱â´Â ÇÁ·Î±×·¥ µÇ¾î ÀÖ´Ù. ¸¸¾à Çì´õ ÆÄÀÏÀÌ `#ifndef' Á¶°Ç ¾î±¸¿¡ ÀüüÀûÀ¸·Î Æ÷ÇԵǾî ÀÖÀ¸¸é °ø¹é°ú ÁÖ¼®À» ±ÔÄ¢À¸·Î Çؼ ±×°ÍÀº »ç½Ç·Î ±â¾ï µÈ´Ù. ¸¸¾à `#include'ÀÌ °°Àº ÆÄÀÏÀ» ÁöÁ¤ÇÏ°í `#ifndef'¿¡ ¸ÅÅ©·Î´Â ÀÌ¹Ì Á¤ÀÇ µÇ¾î ÀÖÀ¸¸é Áö½Ã¹®Àº ÁöÁ¤µÈ ÆÄÀÏ ¸ðµÎ¸¦ ó¸®ÇÏÁö ¾Ê°í °Ç³Ê¶Ù¾î Áø´Ù.
In the Objective C language, there is a variant of `#include' called `#import' which includes a file, but does so at most once. If you use `#import' instead of `#include', then you don't need the conditionals inside the header file to prevent multiple execution of the contents.
Objective ¾¾ ¾ð¾î¿¡´Â ÆÄÀÏÀ» Æ÷ÇÔÇÏÁö¸¸ ÃÖ´ëÇÑ Çѹø¸¸ Æ÷ÇÔÇÏ´Â '#import'·Î ºÒ·ÁÁö´Â '#include'ÀÇ º¯ÇüÀº ÀÖ´Ù. ¸¸¾à ´ç½ÅÀÌ '#include'´ë½Å¿¡ '#import'À» »ç¿ëÇÑ´Ù¸é, ´ç½ÅÀº ³»¿ëµéÀÇ ´ÙÁß ½ÇÇàÀ» ¹æÁöÇϱâ À§ÇÑ Çì´õ ÆÄÀÏ ¾È¿¡ Á¶°Ç ¾î±¸µéÀÌ ÇÊ¿äÇÏÁö ¾Ê´Ù.
`#import' is obsolete because it is not a well designed feature. It requires the users of a header file -- the applications programmers --- to know that a certain header file should only be included once. It is much better for the header file's implementor to write the file so that users don't need to know this. Using `#ifndef' accomplishes this goal.
'#import'Àº Àß ¼³°èµÈ ÇüÅ°¡ ¾Æ´Ï±â ¶§¹®¿¡ ¾µ¸ð ¾ø´Ù. ±×°ÍÀº ¾î¶² Çì´õ ÆÄÀÏ ¿ÀÁ÷ ÇÑ ¹ø Æ÷ÇԵǾî¾ß ÇÏ´Ù´Â °ÍÀ» ¾Ë°í ÀÖ´Â »ç¿ëÀÚµéÀ» ¿ä±¸ÇÑ´Ù --ÀÀ¿ë ÇÁ·Î±×·¡¸Óµé --- Çì´õ ÆÄÀÏÀÇ ÀÛ¼ºÀÚ°¡ »ç¿ëÀÚµéÀÌ ÀÌ°ÍÀ» ¾Æ´Â °ÍÀÌ ÇÊ¿äÇÏÁö ¾Êµµ·Ï ÆÄÀÏ¿¡ ±â·ÏÇÏ´Â °ÍÀº ÈξÀ ´õ ÁÁ´Ù. '#ifndef'À» »ç¿ëÇÔÀ¸·Î½á ÀÌ ¸ñÇ¥¸¦ ´Þ¼ºÇÑ´Ù.
Inheritance is what happens when one object or file derives some of its contents by virtual copying from another object or file. In the case of C header files, inheritance means that one header file includes another header file and then replaces or adds something.
»ó¼ÓÀº ¾î¶² °´Ã¼ ¶Ç´Â ÆÄÀÏÀÌ ´Ù¸¥ °´Ã¼³ª ÆÄÀϷκÎÅÍ °¡»óÀûÀÎ º¹»ç¿¡ ÀÇÇØ ÆÄ»ýµÇ¾î Áú ¶§ ÀϾ´Â °ÍÀÌ´Ù. C Çì´õ ÆÄÀϵéÀÇ °æ¿ì, »ó¼ÓÀº ÇÑ Çì´õÆÄÀÏÀÌ ´Ù¸¥ Çì´õÆÄÀÏÀ» Æ÷ÇÔÇÏ°í ±× ÈÄ¿¡ ´ëüµÇ°Å³ª ¹«¾ð°¡ ´õÇØÁö´Â °ÍÀ» ÀǹÌÇÑ´Ù.
If the inheriting header file and the base header file have different names, then inheritance is straightforward: simply write `#include "base"' in the inheriting file.
¸¸¾à »ó¼ÓµÈ Çì´õ ÆÄÀÏ°ú º£À̽º Çì´õ ÆÄÀÏÀÌ ´Ù¸¥ À̸§µéÀ» °®°í ÀÖ´Ù¸é, »ó¼ÓÀº Á÷¼±ÀûÀÌ´Ù.: °£´ÜÇÏ°Ô »ó¼Ó ¹Þ´Â ÆÄÀÏ¿¡ `#include "base" '·Î ¾´´Ù.
Sometimes it is necessary to give the inheriting file the same name as the base file. This is less straightforward.
¶§¶§·Î º£À̽º ÆÄÀÏ°ú °°Àº À̸§À» »ó¼ÓÇÑ ÆÄÀÏ¿¡ ÁÖ´Â °ÍÀÌ ÇÊ¿äÇÑ´Ù. ÀÌ°ÍÀº ´ú Á÷¼±ÀûÀÌ´Ù.
For example, suppose an application program uses the system header `sys/signal.h', but the version of `/usr/include/sys/signal.h' on a particular system doesn't do what the application program expects. It might be convenient to define a "local" version, perhaps under the name `/usr/local/include/sys/signal.h', to override or add to the one supplied by the system.
¿¹¸¦ µé¸é, ÀÀ¿ë ÇÁ·Î±×·¥ÀÌ ½Ã½ºÅÛ Çì´õ ÆÄÀÏ ' sys/signal.h'¸¦ »ç¿ëÇÑ´Ù°í »ý°¢ÇØ º¸ÀÚ. ±×·¯³ª Ưº°ÇÑ ½Ã½ºÅÛ¿¡ '/usr/include/sys/signal.h'ÀÇ ¹öÀüÀº ÀÀ¿ë ÇÁ·Î±×·¥ÀÌ ±â´ëÇÑ °ÍÀ» ÇÏÁö ¾Ê´Â´Ù. ¾Æ¸¶µµ /usr/local/include/sys/signal.h' À̸§À¸·Î ½Ã½ºÅÛ¿¡ ÀÇÇؼ °ø±ÞµÈ °ÍÀ» ¿À¹ö¶óÀ̵åÇϰųª Áõ°¡½ÃÅ°±â À§ÇÏ¿© Áö¿ª ¹öÀüÀ» ±ÔÁ¤ÇÏ´Â °ÍÀÌ Æí¸®ÇÒ °ÍÀÌ´Ù.
You can do this by compiling with the option `-I.', and writing a file `sys/signal.h' that does what the application program expects. Making this file include the standard `sys/signal.h' is not so easy --- writing `#include <sys/signal.h>' in that file doesn't work, because it includes your own version of the file, not the standard system version. Used in that file itself, this leads to an infinite recursion and a fatal error in compilation.
´ç½ÅÀº ' £I.'¿É¼ÇÀ¸·Î ÄÄÆÄÀÏÇÔÀ¸·Î½á ÀÌ°ÍÀ» ÇÒ ¼ö ÀÖ´Ù.±×¸®°í ÀÀ¿ë ÇÁ·Î±×·¥ÀÌ ±â´ëÇÏ´Â °ÍÀ» ÇÏ´Â 'sys/signal.h'¸¦ ¾µ ¼ö ÀÖ´Ù. Ç¥ÁØ 'sys/signal.h'À» Æ÷ÇÔÇÏ´Â ÆÄÀÏÀ» ¸¸µå´Â °ÍÀº ±×·¸°Ô ½±Áö ¾Ê´Ù -- Ç¥ÁØ ½Ã½ºÅÛ ¹öÀüÀÌ ¾Æ´Ï¶ó ´ç½ÅÀÇ ÆÄÀÏ ¹öÀüÀ̱⠶§¹®¿¡ `#include <sys/signal.h>'´Â ÀÛµ¿ÇÏÁö ¾Ê´Â´Ù. Used in that file itself, ÀÌ°ÍÀº ¹«ÇÑ Àç±ÍÈ£Ãâ°ú Ä¡¸íÀûÀÎ ÄÄÆÄÀÏ ¿¡·¯¸¦ ÃÊ·¡ ÇÑ´Ù.
`#include </usr/include/sys/signal.h>' would find the proper file, but that is not clean, since it makes an assumption about where the system header file is found. This is bad for maintenance, since it means that any change in where the system's header files are kept requires a change somewhere else.
' #include</usr/include/sys/signal.h>´Â Àû´çÇÑ ÆÄÀÏÀ» ¹ß°ßÇÒ °ÍÀÌ´Ù. ±×·¯³ª ½Ã½ºÅÛ Çì´õ ÆÄÀÏÀÌ ¹ß°ßµÇ´Â °÷À» °¡Á¤Çϱ⠶§¹®¿¡ ±×°ÍÀº ±ú²ýÇÏÁö ¾Ê´Ù. º¸Á¸µÇ´Â ½Ã½ºÅÛ Çì´õÆÄÀÏ¿¡ ¾î¶°ÇÑ º¯Èµµ ´Ù¸¥ °÷¿¡¼ÀÇ º¯È¸¦ ¿ä±¸Çϱ⠶§¹®¿¡ ÀÌ°ÍÀº À¯Áöº¸¼ö¿¡ ³ª»Ú´Ù..
The clean way to solve this problem is to use `#include_next', which means, "Include the next file with this name." This directive works like `#include' except in searching for the specified file: it starts searching the list of header file directories after the directory in which the current file was found.
ÀÌ ¹®Á¦¸¦ ÇØ°áÇÒ ±ò²ûÇÑ(^^;) ¹æ¹ýÀº '#include_next'À» »ç¿ëÇÏ´Â ÀÌ´Ù. ÀÌ '#include_next'Àº "ÀÌ À̸§À¸·Î next ÆÄÀÏÀ» Æ÷ÇÔÇضó" ¶ó´Â °ÍÀ» ÀǹÌÇÑ´Ù. ÀÌ Áö½Ã¹®Àº ƯÁ¤ÇÑ ÆÄÀÏÀ» ã´Â °ÍÀ» Á¦¿ÜÇÏ°í '#include'ó·³ ÀÛµ¿ÇÑ´Ù : ÇöÀç ÆÄÀÏÀÌ ¹ß°ßµÇ¾ú´ø µð·ºÅ丮 ´ÙÀ½¿¡ Çì´õ ÆÄÀÏ µð·ºÅ丮µéÀÇ ¸®½ºÆ®ÀÇ Å½»öÀ» ½ÃÀÛÇÑ´Ù.
Suppose you specify `-I /usr/local/include', and the list of directories to search also includes `/usr/include'; and suppose both directories contain `sys/signal.h'. Ordinary `#include <sys/signal.h>' finds the file under `/usr/local/include'. If that file contains `#include_next <sys/signal.h>', it starts searching after that directory, and finds the file in `/usr/include'.
´ç½ÅÀÌ `-I /usr/local/include'¸¦ ÁöÁ¤ÇÏ°í, ã±â À§ÇÑ µð·ºÅ丮 ¸®½ºÆ®´Â `/usr/include'¸¦ Æ÷ÇÔÇÑ´Ù°í °¡Á¤ÇÏÀÚ: ±×¸®°í `sys/signal.h'¸¦ ´ã°í ÀÖ´Â µð·ºÅ丮µµ °¡Á¤ÇÏÀÚ. ÀϹÝÀûÀ¸·Î `#include <sys/signal.h>'´Â `/usr/local/include'¾Æ·¡¼ ã´Â´Ù. ¸¸¾à ±× ÆÄÀÏÀÌ`#include_next <sys/signal.h>'¸¦ Æ÷ÇÔÇÏ°í ÀÖ´Ù¸é ±× µð·ºÅ丮 ´ÙÀ½¿¡ Ž»öÀ» ½ÃÀÛÇÏ°í `/usr/include'¿¡¼ ÆÄÀÏÀ» ã´Â´Ù.
`#include_next' is a GCC extension and should not be used in programs intended to be portable to other compilers.
'#include_next'Àº GCC È®ÀåÀÌ°í ´Ù¸¥ ÄÄÆÄÀÏ·¯µé¿¡ ½Æµµ·Ï µÈ ÇÁ·Î±×·¥µé¿¡ »ç¿ëµÇÁö ¾Ê¾Æ¾ß ÇÑ´Ù.
The header files declaring interfaces to the operating system and runtime libraries often cannot be written in strictly conforming C. Therefore, GNU C gives code found in system headers special treatment. Certain categories of warnings are suppressed, notably those enabled by `-pedantic'.
¿î¿µÃ¼Á¦¿Í ·±Å¸ÀÓ ¶óÀ̺귯¸®µé¿¡ ÀÎÅÍÆäÀ̽º·Î ¼±¾ðµÈ Çì´õ ÆÄÀϵéÀº ¾ö¹ÐÇÏ°Ô C¿¡ µû¸£µµ·Ï ¾²¿©ÁöÁö ¾Ê´Â´Ù. ±×·¡¼ GNU C´Â Ưº°ÇÏ°Ô ´Ù·ç¾îÁø ½Ã½ºÅÛ ÆÄÀϵ鿡 Äڵ带 Á¦°ø ÇÑ´Ù. ¾î¶² Á¾·ùÀÇ °æ°íµéÀº `-pedantic'·Î È®½ÇÇÏ°Ô ¾ïÁ¦ µÇ¾îÁø´Ù.
Normally, only the headers found in specific directories are considered system headers. The set of these directories is determined when GCC is compiled. There are, however, two ways to add to the set.
ÀϹÝÀûÀ¸·Î ƯÁ¤ µð·ºÅ丮µé¿¡¼¸¸ ¹ß°ßµÇ´Â Çì´õµéÀº ½Ã½ºÅÛ Çì´õµé·Î »ý°¢µÈ´Ù.ÀÌ µð·ºÅ丮µéÀÇ ÁýÇÕÀº GCC·Î ÄÄÆÄÀÏ µÉ ¶§ °áÁ¤µÇ¾îÁø´Ù. ±×·¯³ª, 2°¡Áö ¹æ¹ýÀ» ÀÌ ÁýÇÕ¿¡ ´õÇß´Ù.
The `-isystem' command line option adds its argument to the list of directories to search for headers, just like `-I'. In addition, any headers found in that directory will be considered system headers. Note that unlike `-I', you must put a space between `-isystem' and its argument.
`£isystem' ¸í·É ¶óÀÎ ¿É¼ÇÀº Çì´õµéÀ» ã±â À§ÇÏ¿© µð·ºÅ丮µéÀÇ ¸®½ºÆ®¿¡ ±×°ÍÀÇ ÀÎÀÚ¸¦ ´õÇÑ´Ù. `-l' ¿É¼Ç°ú °°´Ù. µ¡ºÙ¿© ¸»ÇÏÀÚ¸é, ¾î¶² Çì´õµéµµ ½Ã½ºÅÛ Çì´õµé·Î »ý°¢µÇ´Â µð·ºÅ丮¿¡¼ ã´Â´Ù. ÁÖÀÇ ÇÒ °ÍÀº '£I'¿Í´Â ´Þ¸®, ´ç½ÅÀº '£isystem'¿Í ±×°ÍÀÇ ÀÎÀÚ»çÀÌ¿¡ °ø°£À» ³õ¾Æ¾ß¸¸ ÇÑ´Ù´Â °ÍÀÌ´Ù..
All directories named by `-isystem' are searched after all directories named by `-I', no matter what their order was on the command line. If the same directory is named by both `-I' and `-isystem', `-I' wins; it is as if the `-isystem' option had never been specified at all.
¸í·É ¶óÀο¡ ±×µéÀÇ ¼ø¼°¡ ¹«¾ùÀ̵çÁö `-I'¿¡ ÀÇÇØ ºÒ¸° ¸ðµç µð·ºÅ丮ÀÇ Å½»ö ÈÄ¿¡ '£isystem'¿¡ ÀÇÇØ ºÒ¸° ¸ðµç µð·ºÅ丮µéÀÌ Å½»ö µÈ´Ù. ¸¸¾à `-I' °ú`-isystem' ¸ðµÎ µð·ºÅ丮 À̸§ÀÌ °°À¸¸é `-I'°¡ ¿ì¼±ÀÌ´Ù; `-isystem' ¿É¼ÇÀº °áÄÚ ÁöÁ¤µÇÁö ¾Ê´Â °Í°ú ¸¶Âù°¡Áö´Ù.
There is also a directive, `#pragma GCC system_header', which tells GCC to consider the rest of the current include file a system header, no matter where it was found. Code that comes before the `#pragma' in the file will not be affected.
¾îµð¼ ã¾ÆÁöµç ÇöÀçinclude ½Ã½ºÅÛ Çì´õ ÆÄÀÏÀÇ ³ª¸ÓÁö¸¦ GCC·Î ¿©±â´Â `#pragma GCC system_header' Áö½Ã¹® ¶ÇÇÑ ÀÖ´Ù. ÆÄÀÏ¿¡¼ `#pragma' ÀÌÀü¿¡ ¿À´Â ÄÚµå´Â ¿µÇâ ¹ÞÁö ¾ÊÀ» °ÍÀÌ´Ù.
`#pragma GCC system_header' has no effect in the primary source file.
`#pragma GCC system_header'´Â Ãʱ⠼ҽº¿¡ È¿·ÂÀÌ ¾ø´Ù.
A macro is a sort of abbreviation which you can define once and then use later. There are many complicated features associated with macros in the C preprocessor.
¸ÅÅ©·Î´Â ÇÑ ¹ø Á¤ÀǸ¦ ³»¸± ¼ö ÀÖ°í ±× ´ÙÀ½¿¡ ³ªÁß¿¡ »ç¿ëÇÏ´Â abbreviation Á¾·ùÀÌ´Ù. C Àü󸮱⿡´Â ¸ÅÅ©·Î¿Í ¿¬°üµÈ º¹ÀâÇÑ Æ¯Â¡ÀÌ ¸¹ÀÌ ÀÖ´Ù.
An object-like macro is a kind of abbreviation. It is a name which stands for a fragment of code. Some people refer to these as manifest constants.
object-like macro´Â abbreviationÀÇ ÀÏÁ¾ÀÌ´Ù. ±×°ÍÀº ÄÚµå Á¶°¢À» ³ªÅ¸³»´Â À̸§ÀÌ´Ù. ¾î¶² »ç¶÷µéÀº ¸í¹éÇÑ »ó¼öµé·Î¼ À̰͵éÀ» »ý°¢ÇÑ´Ù.
Before you can use a macro, you must define it explicitly with the `#define' directive. `#define' is followed by the name of the macro and then the token sequence it should be an abbreviation for, which is variously referred to as the macro's body, expansion or replacement list. For example,
´ç½ÅÀÌ ¸ÅÅ©·Î¸¦ »ç¿ëÇÒ ¼ö ÀÖ±â Àü¿¡´Â ¸í½ÃÀûÀ¸·Î `#define' Áö½Ã¹®°ú ÇÔ²² Á¤ÀÇ Çؾ߸¸ ÇÑ´Ù. `#define' ´ÙÀ½¿¡´Â ¸ÅÅ©·ÎÀÇ À̸§ÀÌ µû¸¥´Ù. ±× ´ÙÀ½¿¡´Â ¸ÅÅ©·ÎÀÇ ¸öü, È®Àå ¶Ç´Â ±³Ã¼ÇÒ ¸®½ºÆ®·Î½á abbreviation µÇ¾î¾ß ÇÏ´Â ÅäÅ« ¿ÀÌ ¿Â´Ù.
#define BUFFER_SIZE 1020
defines a macro named `BUFFER_SIZE' as an abbreviation for the token `1020'. If somewhere after this `#define' directive there comes a C statement of the form
`BUFFER_SIZE'´Â `1020' ÅäÅ«¿¡ abbreviation·Î À̸§ Áö¾îÁø ¸ÅÅ©·Î·Î Á¤ÀÇ µÈ´Ù. ÀÌ `#define'Áö½Ã¹® ÈÄ¿¡ ¾îµð¿¡¼ ±× Çü½ÄÀÇ C¼¼úÀÌ ¿À¸é,
foo = (char *) xmalloc (BUFFER_SIZE);
then the C preprocessor will recognize and expand the macro `BUFFER_SIZE', resulting in
±× ´ÙÀ½¿¡ C Àü󸮱â´Â ¾È¿¡ °á°ú·Î¼ »ý±ä ¸ÅÅ©·Î 'BUFFER_SIZE'¸¦ ÀνÄÇÒ °ÍÀÌ°í È®ÀåÇÒ °ÍÀÌ´Ù.
foo = (char *) xmalloc (1020);
The use of all upper case for macro names is a standard convention. Programs are easier to read when it is possible to tell at a glance which names are macros.
¸ÅÅ©°í À̸§µéÀ» À§ÇÑ ´ë¹®ÀÚ »ç¿ëÀº ÀϹÝÀûÀÎ °ü·ÊÀÌ´Ù. ÇÁ·Î±×·¥µéÀº ¸ÅÅ©·Î À̸§µéÀ» Èê±ß º¸´Â °Å½Ã °¡´ÉÇÒ ¶§ Àб⠽±´Ù.
Normally, a macro definition can only span a single logical line, like all C preprocessing directives. Comments within a macro definition may contain newlines, which make no difference since each comment is replaced by a space regardless of its contents.
ÀϹÝÀûÀ¸·Î, ¸ÅÅ©·Î Á¤ÀÇ´Â ¸ðµç CÀüó¸® Áö½Ã¹®Ã³·³ ÇϳªÀÇ ³í¸® ¶óÀÎÀ¸·Î¸¸ ³õÀÏ ¼ö ÀÖ´Ù. ¸ÅÅ©·Î ³»¿¡¼ ÁÖ¼®µéÀº newlineµé·Î Æ÷ÇÔ µÉÁö ¸ð¸¥´Ù. ±×·¯³ª °¢ ÁÖ¼®ÀÌ ±×°ÍÀÇ ³»¿ë¿¡ »ó°ü ¾ø´Â °ø°£À¸·Î ´ëü µÇ±â ¶§¹®¿¡ Â÷ÀÌÁ¡ÀÌ ¾ø´Ù.
Apart from this, there is no restriction on what can go in a macro body provided it decomposes into valid preprocessing tokens. In particular, parentheses need not balance, and the body need not resemble valid C code. (If it does not, you may get error messages from the C compiler when you use the macro.)
ÀÌ°Í°ú´Â º°°³·Î, ¿Ã¹Ù¸¥ Àüó¸® ÅäÅ«µé·Î ºÐÇØÇϵµ·Ï Á¦°øµÈ ¸ÅÅ©·Î body·Î °¥ ¼ö ÀÖ´Â °Í¿¡´Â Á¦ÇÑÀÌ ¾ø´Ù. ƯÈ÷ °ýÈ£µéÀº ±ÕÇüÀÌ ÇÊ¿ä ¾ø°í ¸öü´Â ¿Ã¹Ù¸¥CÄÚµå¿Í ´àÀ» ÇÊ¿ä´Â ¾ø´Ù.(±×·¸Áö ¾ÊÀ¸¸é ´ç½ÅÀÌ ¸ÅÅ©·Î¸¦ ÀÌ¿ëÇÒ ¶§ C ÄÄÆÄÀÏ·¯·ÎºÎÅÍ ¿¡·¯ ¸Þ½ÃÁö¸¦ ¹Þ°Ô µÉ Áö ¸ð¸¥´Ù.)
The C preprocessor scans your program sequentially, so macro definitions take effect at the place you write them. Therefore, the following input to the C preprocessor
Àü󸮱â´Â ¿¬¼ÓÀûÀ¸·Î ´ç½ÅÀÇ ÇÁ·Î±×·¥À» °Ë»öÇÑ´Ù. ±×·¡¼ ´ç½ÅÀÌ ¸ÅÅ©·Î¸¦ ¾´ °÷¿¡¼ ¸ÅÅ©·Î Á¤ÀÇ°¡ È¿°ú°¡ ÀÖ°Ô ÇÑ´Ù. ±×·¯¹Ç·Î, C Àü󸮱⿡ ÀÔ·ÂÀÌ µÚ µû¸¥´Ù.
foo = X; #define X 4 bar = X;
produces as output
Ãâ·ÂÀ» ¸¸µç´Ù.
foo = X; bar = 4;
When the preprocessor expands a macro name, the macro's expansion replaces the macro invocation, and the result is re-scanned for more macros to expand. For example, after
Àü󸮱Ⱑ ¸ÅÅ©·Î À̸§À» È®ÀåÇÒ ¶§, ¸ÅÅ©·ÎÀÇ È®ÀåÀº ¸ÅÅ©·Î È£ÃâÀ» ¹Ù²Û´Ù. ±×¸®°í °á°ú´Â ´Ù½Ã ¸ÅÅ©·Î È®ÀåÀ» À§ÇØ ´Ù½Ã °Ë»öµÈ´Ù. ¿¹¸¦ µé¸é,
#define BUFSIZE 1020 #define TABLESIZE BUFSIZE
the name `TABLESIZE' when used in the program would go through two stages of expansion, resulting ultimately in `1020'.
`TABLESIZE' À̸§ÀÌ ÇÁ·Î±×·¥¿¡¼ »ç¿ë µÉ ¶§ µÎ°¡Áö È®Àå ½ºÅ×ÀÌÁö¸¦ Åë°úÇÏ°í ¸¶Ä§³» `1020¡¯¶õ °á°ú°¡ ³ª¿Â´Ù.
This is not the same as defining `TABLESIZE' to be `1020'. The `#define' for `TABLESIZE' uses exactly the expansion you specify -- in this case, `BUFSIZE' -- and does not check to see whether it too contains macro names. Only when you use `TABLESIZE' is the result of its expansion scanned for more macro names. See section Cascaded Use of Macros.
ÀÌ°ÍÀº `1020'°¡ `TABLESIZE'·Î Á¤ÀÇ µÇ´Â °Í°ú °°Áö ¾Ê´Ù. `TABLESIZE'¸¦ À§ÇÑ `#define'´Â Á¤È®ÇÏ°Ô ´ç½ÅÀÌ ÁöÁ¤ÇÑ È®ÀåÀ» ÀÌ¿ëµÈ´Ù.ÀÌ °æ¿ì¿¡´Â `BUFSIZE'ÀÌ´Ù ±×¸®°í ¸ÅÅ©·Î À̸§µéÀ» Æ÷ÇÔÇß´ÂÁö ¾Ê¾Ò´ÂÁö¸¦ º¸±â À§Çؼ üũÇÏÁö´Â ¾Ê´Â´Ù.
An object-like macro is always replaced by exactly the same tokens each time it is used. Macros can be made more flexible by taking arguments. Arguments are fragments of code that you supply each time the macro is used. These fragments are included in the expansion of the macro according to the directions in the macro definition. A macro that accepts arguments is called a function-like macro because the syntax for using it looks like a function call.
object-like ¸ÅÅ©·Î´Â Á¤È®ÇÏ°Ô ¸Å¹ø °°Àº ÅäÅ«µé·Î Ç×»ó ´ëü µÈ´Ù. ¸ÅÅ©·Î´Â ÀÎÀÚµéÀ» Á» ´õ À¯¿¬ÇÏ°Ô ¹Þ¾Æ µéÀÏ ¼ö ÀÖ´Ù. ÀÎÀÚµéÀº ´ç½ÅÀÌ ¸ÅÅ©·Î°¡ ÀÌ¿ë µÉ ¶§ ¸¶´Ù Á¦°ø µÇ´Â ÄÚµåÀÇ Á¶°¢µéÀÌ´Ù. ÀÌ Á¶°¢µéÀº ¸ÅÅ©·Î Á¤ÀÇ¿¡ ¹æÇâÀ» µû¶ó ¸ÅÅ©·Î È®Àå¿¡ Æ÷ÇÔ µÈ´Ù. ÀÎÀÚ¸¦ ¹Þ¾ÆµéÀÌ´Â ¸ÅÅ©·Î´Â function-like ¸ÅÅ©·Î·Î ºÒ¸®´Âµ¥ ±×°ÍÀ» »ç¿ëÇÏ´Â ¹®¹ýÀÌ ÇÔ¼ö È£Ãâ°ú °°ÀÌ º¸À̱⠶§¹®ÀÌ´Ù.
To define a macro that uses arguments, you write a `#define' directive with a list of parameters in parentheses after the name of the macro. The parameters must be valid C identifiers, separated by commas and optionally whitespace. The `(' must follow the macro name immediately, with no space in between. If you leave a space, you instead define an object-like macro whose expansion begins with a `(', and often leads to confusing errors at compile time.
ÀÎÀÚ¸¦ ÀÌ¿ëÇÏ´Â ¸ÅÅ©·Î¸¦ Á¤ÀÇ Çϱâ À§Çؼ ´ç½ÅÀº ¸ÅÅ©·Î À̸§ µÚ¿¡ °ýÈ£·Î ÆĶó¹ÌÅÍÀÇ ¸®½ºÆ®¸¦ ÁöÁ¤Çؼ `#define'¸¦ ¾´´Ù. ÆĶó¹ÌÅ͵éÀº ÄÞ¸¶¿Í ¼±ÅÃÀûÀÎ °ø¹éÀ¸·Î ºÐ¸®µÈ ¿Ã¹Ù¸¥ C ½Äº°ÀÚ¿©¾ß¸¸ ÇÑ´Ù. `('´Â °ø°£ ¾øÀÌ ¸ÅÅ©·Î À̸§ µÚ¿¡ ¹Ù·Î ¿Í¾ß ÇÑ´Ù. ¸¸¾à °ø°£ÀÌ ³²À¸¸é, ´ë½Å¿¡ ´ç½ÅÀº `(' ·Î ½ÃÀÛÇÏ´Â object-like ¸ÅÅ©·Î¸¦ Á¤ÀÇÇÏ°Ô µÈ°í ÄÄÆÄÀÏ ½Ã º¹ÀâÇÑ ¿¡·¯¸¦ ÀÚÁÖ ÃÊ·¡ÇÏ°Ô µÈ´Ù.
As an example, here is a macro that computes the minimum of two numeric values, as it is defined in many C programs:
ÇÑ ¿¹·Î, ¸¹Àº C ÇÁ·Î±×·¥µé¿¡¼ Á¤ÀÇ µÇ´Â µÎ °³ÀÇ ¼ýÀÚ °ª¿¡¼ ÀÛÀº °ªÀ» °è»êÇÏ´Â ¸ÅÅ©·Î°¡ ÀÖ´Ù.
#define min(X, Y) ((X) < (Y) ? (X) : (Y))
(This is not the best way to define a "minimum" macro in GNU C. See section Duplication of Side Effects, for more information.)
( ÀÌ°ÍÀº GNU C¿¡¼ "minimum" ¸ÅÅ©·Î¸¦ Á¤ÀÇ ÇÏ´Â Á¦ÀÏ ÁÁÀº ¹æ¹ýÀº ¾Æ´Ï´Ù. ´õ ¸¹Àº Á¤º¸¸¦ À§ÇØ Duplication of Side Effects ºÎºÐÀ» ºÁ¶ó. ) .
To invoke a function-like macro, you write the name of the macro followed by a list of arguments in parentheses, separated by commas. The invocation of the macro need not be restricted to a single logical line - it can cross as many lines in the source file as you wish. The number of arguments you give must match the number of parameters in the macro definition; empty arguments are fine. Examples of use of the macro `min' include `min (1, 2)' and `min (x + 28, *p)'.
function-like ¸ÅÅ©·Î¸¦ È£ÃâÇϱâ À§Çؼ ´ç½ÅÀº ¸ÅÅ©·Î À̸§ À§¿¡ °ýÈ£¿¡ ÄÞ¸¶·Î ºÐ¸®µÈ ÀÎÀÚµéÀÇ ¸®½ºÆ®°¡ ¿Àµµ·Ï ¸ÅÅ©·Î¸¦ ¾´´Ù. ¸ÅÅ©·Î È£ÃâÀº ÇϳªÀÇ ³í¸®Àû ¶óÀÎÀ¸·Î Á¦ÇÑ µÉ ÇÊ¿ä´Â ¾ø´Ù.- ±×°ÍÀº ´ç½ÅÀÌ ¿øÇÏ´Â ¸¸Å ¼Ò½º ÆÄÀÏ¿¡ ¸¹Àº ¶óÀÎÀ¸·Î ³õÀ» ¼ö ÀÖ´Ù. ´ç½ÅÀº ÀÎÀÚµéÀÇ ¼ö¸¦ ¸ÅÅ©·Î Á¤ÀÇ¿¡¼ÀÇ ÆĶó¹ÌÅÍÀÇ ¼ö¿Í ÀÏÄ¡ ½ÃÄÑ¾ß ÇÑ´Ù; ºó ÀÎÀÚµéÀº ±¦Âú´Ù. `min' ¸ÅÅ©·ÎÀÇ ¿¹·Î `min (1, 2)'°ú `min (x + 28, *p)'¸¦ Æ÷ÇÔÇÑ´Ù.
The expansion text of the macro depends on the arguments you use. Each macro parameter is replaced throughout the macro expansion with the tokens of the corresponding argument. Leading and trailing argument whitespace is dropped, and all whitespace between the tokens of an argument is reduced to a single space. Using the same macro `min' defined above, `min (1, 2)' expands into
¸ÅÅ©·ÎÀÇ È®Àå ÅؽºÆ®´Â ´ç½ÅÀÌ »ç¿ëÇÏ´Â ÀÎÀÚ¿¡ ÀÇÁ¸ÇÑ´Ù. °¢ ¸ÅÅ©·Î ÆĶó¹ÌÅÍ´Â ÀÏÄ¡ÇÏ´Â ÀÎÀÚÀÇ ÅäÅ«À¸·Î ¸ÅÅ©·Î È®ÀåÀ» ÅëÇØ ´ëü µÈ´Ù. óÀ½°ú ¸¶Áö¸· ÀÎÀÚ °ø¹éÀº Á¦°Å µÇ°í ÀÎÀÚÀÇ ÅäÅ« »çÀÌÀÇ ¸ðµç °ø¹éÀº ÇϳªÀÇ °ø°£À¸·Î ÁÙ¾îµç´Ù. À§¿¡¼ Á¤ÀÇµÈ `min'°°Àº ¸ÅÅ©·Î¸¦ ÀÌ¿ëÇؼ, `min (1, 2)'·Î È®ÀåÇϸé,
((1) < (2) ? (1) : (2))
where `1' has been substituted for `X' and `2' for `Y'.
`1'Àº `X'¿¡¼ ´ëü µÇ¾ú°í `2'´Â `Y'¿¡¼ ´ëü ‰ç´Ù.
Likewise, `min (x + 28, *p)' expands into
ºñ½ÁÇÏ°Ô `min (x + 28, *p)'µµ È®Àå µÈ´Ù
((x + 28) < (*p) ? (x + 28) : (*p))
Parentheses within each argument must balance; a comma within such parentheses does not end the argument. However, there is no requirement for square brackets or braces to balance, and they do not prevent a comma from separating arguments. Thus,
°¢ ÀÎÀÚ ³»¿¡¼ °ýÈ£´Â ±ÕÇü ¸Â°Ô ¾²¿©¾ß¸¸ ÇÑ´Ù; ±×·± °ýÈ£ ³»¿¡¼ ÄÞ¸¶´Â ÀÎÀÚÀÇ ³¡ÀÌ ¾Æ´Ï´Ù. ±×·¯³ª, ±ÕÇüÀ» À§ÇØ square brackets ¶Ç´Â braces´Â ÇÊ¿ä ¾ø°í ºÐ¸®µÈ ÀÎÀڷκÎÅÍ ÄÞ¸¶¸¦ ¸·Áö ¾Ê´Â´Ù. °Ô´Ù°¡,
macro (array[x = y, x + 1])
passes two arguments to macro
: `array[x = y' and `x +
1]'. If you want to supply `array[x = y, x + 1]' as an argument,
you must write it as `array[(x = y, x + 1)]', which is equivalent C
code.
¸ÅÅ©·Î¿¡¼ µÎ°³ÀÇ ÀÎÀÚµéÀ» Åë°ú ½ÃŲ´Ù: `array[x = y' and `x + 1]¡¯. ¸¸¾à ´ç½ÅÀÌ ÀÎÀڷνá `array[x = y, x + 1]'¸¦ Á¦°øÇÑ´Ù¸é C ÄÚµå¿Í °°°Ô `array[(x = y, x + 1)]'À» ½á¾ß¸¸ ÇÑ´Ù.
After the arguments have been substituted into the macro body, the resulting expansion replaces the macro invocation, and re-scanned for more macro calls. Therefore even arguments can contain calls to other macros, either with or without arguments, and even to the same macro. For example, `min (min (a, b), c)' expands into this text:
ÀÎÀÚ°¡ ¸ÅÅ©·Î body·Î ´ëüµÈ ÈÄ¿¡, °á°úÈ®ÀåÀº ¸ÅÅ©·Î È£Ãâ·Î ´ëü µÇ°í ´õ ¸¹Àº ¸ÅÅ©·Î È£ÃâÀ» À§ÇØ ´Ù½Ã °Ë»ö µÈ´Ù. ±×·¯¹Ç·Î ÀÎÀÚ°¡ ¾øµçÁö ÀÖµçÁö, ÀÎÀÚµéÀº ´Ù¸¥ ¸ÅÅ©·ÎµéÀÇ È£ÃâÀ» Æ÷ÇÔ ÇÒ ¼ö ÀÖ°í °°Àº ¸ÅÅ©·Î Á¶Â÷ Æ÷ÇÔ ÇÒ ¼ö ÀÖ´Ù. ¿¹¸¦ µé¸é ,
((((a) < (b) ? (a) : (b))) < (c) ? (((a) < (b) ? (a) : (b))) : (c))
(Line breaks shown here for clarity would not actually be generated.)
(¸í·áÇÏ°Ô ³ªÅ¸³»±â À§ÇØ ¿©±â¿¡ º¸¿©Áø Line breakesµéÀº ½ÇÁ¦·Î ¸¸µé¾îÁöÁö ¾ÊÀ» °ÍÀÌ´Ù )
If a macro foo
takes one argument, and you want to supply an
empty argument, simply supply no preprocessing tokens. Since whitespace
does not form a preprocessing token, it is optional. For example,
`foo ()', `foo ( )' and `bar (, arg2)'.
¸¸¾à foo°¡ ÇϳªÀÇ ÀÎÀÚ¸¦ ¹Þ¾Æ µéÀÌ°í ´ç½ÅÀÌ ÀÎÀÚ°¡ ´Â °ÍÀ» Á¦°øÇϱ⸦ À§ÇÑ ´Ù¸é Àüó¸® ÅäÅ« ¾øÀÌ °£´ÜÇÏ°Ô Á¦°ø ÇÒ ¼ö ÀÖ´Ù. °ø¹éÀº Àüó¸® ÅäÅ«ÀÌ ¾Æ´Ï±â ¶§¹®¿¡, ±×°ÍÀº ¼±ÅÃÀÌ´Ù. ¿¹¸¦ µé¸é `foo()', `foo()' ±×¸®°í `bar(, arg2)'.
Previous GNU preprocessor implementations and documentation were incorrect on this point, insisting that a function-like macro that takes a single argument be passed a space if an empty argument was required.
¸ÅÅ©·Î°¡ ÀÎÀÚ°¡ ¾ø´Â °ÍÀ» ¿ä±¸Çϸé ÇϳªÀÇ ÀÎÀÚ¸¦ ¹Þ¾ÆµéÀÌ´Â function-like´Â °ø°£À¸·Î Áö³ªÃÄ Áø´Ù´Â ÁÖÀåÇÒ ¶§, ¸ÕÀú GNU Àüó¸®ÀÇ ¼öÇà°ú ¹®¼È´Â ÀÌ Á¡¿¡¼ ºÎÁ¤È®ÇÏ´Ù.
If you use a macro name followed by something other than a `(' (after ignoring any whitespace that might follow), it does not form an invocation of the macro, and the preprocessor does not change what you have written. Therefore, it is possible for the same identifier to be a variable or function in your program as well as a macro, and you can choose in each instance whether to refer to the macro (if an actual argument list follows) or the variable or function (if an argument list does not follow). For example,
¸¸¾à (µÚµû¶ó¿Ã ¾î¶² °ø¹éµµ ¹«½ÃÇÑ ÈÄ¿¡) `(' º¸´Ù ´Ù¸¥ ¹«¾ð°¡°¡ ¿À´Â ¸ÅÅ©·Î À̸§À» »ç¿ëÇÑ´Ù¸é, ±×°ÍÀº ¸ÅÅ©·Î È£ÃâÀÇ Çü½ÄÀÌ ¾Æ´Ï°í Àü󸮱â´Â ´ç½ÅÀÌ ¾²´Â °ÍÀ» ¹Ù²ÙÁö ¾Ê´Â´Ù. ±×·¯¹Ç·Î ¸ÅÅ©·Î ¿Í ¸¶Âù°¡Áö·Î °°Àº ½Äº°ÀÚ°¡ ´ç½ÅÀÇ ÇÁ·Î±×·¥¿¡ º¯¼ö¿Í ÇÔ¼ö°¡ µÇ´Â °ÍÀÌ °¡´É ÇÏ´Ù. ±×¸®°í ´ç½ÅÀº ¸ÅÅ©·Î(½ÇÁ¦·Î ÀÎÀÚ¸®½ºÆ®°¡ µÚµû¶ó ¿À¸é)µçÁö º¯¼öµçÁö ÇÔ¼ö( ÀÎÀÚ¸®½ºÆ®°¡ µÚµû¶ó¿ÀÁö ¾ÊÀ¸¸é)µçÁö °¢ ÀνºÅϽºµéÀ» °í¸¦ ¼ö ÀÖ´Ù.
#define foo(X) X foo bar foo(baz)
expands to `foo bar baz'. Such dual use of one name could be confusing and should be avoided except when the two meanings are effectively synonymous: that is, when the name is both a macro and a function and the two have similar effects. You can think of the name simply as a function; use of the name for purposes other than calling it (such as, to take the address) will refer to the function, while calls will expand the macro and generate better but equivalent code.
`foo bar baz'·Î È®ÀåÇß´Ù. ÀÌ·± ÇϳªÀÇ À̸§ÀÇ µÎ °¡Áö »ç¿ëÀº º¹ÀâÇÒ ¼ö ÀÖ´Ù. ±×¸®°í È¿°úÀûÀ¸·Î µÎ °¡Áö Àǹ̰¡ °°°Ô ÇÏ·Á°í ÇÒ ¶§¸¦ Á¦¿ÜÇÏ°í´Â ÇÇÇؾ߸¸ ÇÑ´Ù.:Áï ÇÔ¼ö¿Í ¸ÅÅ©·Î µÎ°¡Áö°¡ ºñ½ÁÇÑ È¿°ú¸¦ °¡Áú ¶§. ´ç½ÅÀº °£´ÜÇÑ À̸§À» ÇÔ¼ö·Î »ý°¢ ÇÒ ¼ö ÀÖ´Ù; ÇÔ¼ö¸¦ È£ÃâÇÏ´Â °Íº¸´Ù ´Ù¸¥ ¸ñÀû(ÁÖ¼Ò¸¦ ¹Þ±â À§ÇØ)ÀÇ À̸§À» »ç¿ëÇÏ´Â °ÍÀº È£ÃâÀÌ ¸ÅÅ©·Î¸¦ È®ÀåÇÏ°í °°Àº Äڵ带 Á¦¿ÜÇÏ°í ´õ ³´°Ô »ý¼ºÇÒ ÇÔ¼ö·Î »ý°¢ µÉ °ÍÀÌ´Ù.
For example, you can use a function named `min' in the same source file that defines the macro. If you write `&min' with no argument list, you refer to the function. If you write `min (x, bb)', with an argument list, the macro is expanded. If you write `(min) (a, bb)', where the name `min' is not followed by an open-parenthesis, the macro is not expanded, so you wind up with a call to the function `min'.
¿¹¸¦ µé¸é, ´ç½ÅÀº ¸ÅÅ©·Î·Î Á¤ÀÇÇÑ `min'À̶ó´Â À̸§À» °°Àº ¼Ò½º¿¡¼ ÇÔ¼ö·Î »ç¿ëÇÒ ¼ö ÀÖ´Ù. ¸¸¾à ÀÎÀÚ ¸®½ºÆ® ¾øÀÌ `&min' ¸¦ ¾²¸é ´ç½ÅÀº ÇÔ¼ö·Î »ý°¢ÇÑ´Ù. ¸¸¾à `min (x, bb)'¸¦ ¾²¸é, ¸ÅÅ©·Î´Â È®Àå µÈ´Ù. ¸¸¾à ´ç½ÅÀÌ `(min) (a, bb)'¸¦ ¾²°í `min' µÚ¿¡ ¿¸° °ýÈ£°¡ ¾øÀ¸¸é ¸ÅÅ©·Î´Â È®ÀåµÇÁö ¾Ê´Â´Ù. ±×·¡¼ ´ç½ÅÀº ÇÔ¼ö `min¡¯À» È£ÃâÇϱâ À§ÇØ ¸¶Áö¸· ¼ÕÁúÀ» ÇÑ´Ù.
In the definition of a macro with arguments, the list of argument names must follow the macro name immediately with no space in between. If there is a space after the macro name, the macro is defined as taking no arguments, and all the rest of the line is taken to be the expansion. The reason for this is that it is often useful to define a macro that takes no arguments and whose definition begins with an identifier in parentheses. This rule makes it possible for you to do either this:
ÀÎÀÚ°¡ ÀÖ´Â ¸ÅÅ©·Î¿¡¼ ÀÎÀÚ À̸§ ¸®½ºÆ®´Â °ø°£ ¾øÀÌ ¸ÅÅ©·Î À̸§ µÚ¿¡ ¹Ù·Î ¿Í¾ß ÇÑ´Ù. ¸¸¾à ¸ÅÅ©·Î À̸§ µÚ¿¡ °ø°£ÀÌ ÀÖÀ¸¸é ¸ÅÅ©·Î´Â ÀÎÀÚ¸¦ ¹Þ¾ÆµéÀÌÁö ¾Ê´Â °ÍÀ¸·Î Á¤ÀÇ µÈ´Ù. ±×¸®°í ¸ðµç ¶óÀÎÀÇ ³ª¸ÓÁö´Â È®ÀåÀÌ µÈ´Ù. ÀÌÀ¯´Â ÀÎÀÚ ¾øÀÌ ¸ÅÅ©·Î°¡ Á¤ÀÇµÇ°í °ýÈ£¿¡ ½Äº°ÀÚ·Î ½ÃÀÛÇÏ´Â ¸ÅÅ©·ÎÀÇ Á¤ÀÇ´Â ÀÚÁÖ À¯¿ëÇϱ⠶§¹®ÀÌ´Ù.
#define FOO(x) - 1 / (x)
(which defines `FOO' to take an argument and expand into minus the reciprocal of that argument) or this:
(`F00'´Â ÀÎÀÚ¸¦ ¹Þ¾Æ µéÀÌ°í À½¼öÀÎ ¿ª¼ö·Î È®ÀåµÇµµ·Ï Á¤ÀǵȴÙ.)
#define BAR (x) - 1 / (x)
(which defines `BAR' to take no argument and always expand into `(x) - 1 / (x)').
( `BAR'´Â ÀÎÀÚ°¡ ¾ø°í Ç×»ó into `(x) - 1 / (x)'·Î È®ÀåµÈ´Ù)
Note that the uses of a macro with arguments can have spaces before the left parenthesis; it's the definition where it matters whether there is a space.
ÀÎÀÚµéÀÌ ÀÖ´Â ¸ÅÅ©·Î¸¦ »ç¿ëÇÏ´Â °ÍÀº ¿ÞÂÊ °ýÈ£ Àü¿¡ °ø°£µéÀ» °¡Áú ¼ö ÀÖ´Ù´Â °Í¿¡ ÁÖÀÇ Çضó; ±×°ÍÀº °ø°£ÀÌ ÀÖ´øÁö ¾ø´øÁö Á¤ÀÇÀÌ´Ù.
ÀÌ ¼½¼ÇÀº ÀüüÀûÀ» Çؼ® ´Ù½Ã ÇؾßÇÔ.
In the ISO C standard of 1999, a macro can be declared to accept a variable number of arguments much as a function can. The syntax for defining the macro is similar to that of a function. Here is an example:
1999³âISO C¿¡¼´Â ¸ÅÅ©·Î°¡ ÇÔ¼öó·³ ¸¹Àº °¡º¯ ¼ýÀÚ¸¦ ÀÎÀÚ·Î ¹Þ¾Æ µå¸± ¼ö ÀÖµµ·Ï ¼±¾ð µÉ ¼ö ÀÖ´Ù. ¸ÅÅ©·Î Á¤ÀÇ ¹®¹ýÀº ÇÔ¼ö¿Í ºñ½ÁÇÏ´Ù. ¿©±â ¿¹°¡ ÀÖ´Ù.
#define eprintf(...) fprintf (stderr, __VA_ARGS__)
Here `...' is a variable argument. In the invocation of
such a macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas. This set of
tokens replaces the identifier __VA_ARGS__
in the macro body
wherever it appears. Thus, we have this expansion:
`...'Àº °¡º¯ ÀÎÀÚÀÌ´Ù. ÀÌ·± ¸ÅÅ©·ÎÀÇ È£Ãâ¿¡¼ È£ÃâÀ» ¸¶Ä¡´Â °ýÈ£¸¦ ´ÝÀ» ¶§ ±îÁö ¾î¶² ÄÞ¸¶µµ Æ÷ÇÔÇϸé¼0 ¶Ç´Â ´õ ¸¹Àº ÅäÅ«µéÀ» Ç¥ÇöÇÑ´Ù. ÀÌ ÅäÅ« ¼³Á¤Àº ¸ÅÅ©·Î body¿¡ __VA_ARGS__°¡ ³ªÅ¸³ª´Â ¾îµðµçÁö ´ëüµÈ´Ù. °Ô´Ù°¡ ¿ì¸®´Â ÀÌ°ÍÀ» È®ÀåÀ» °¡Áö°í ÀÖ´Ù.
eprintf ("%s:%d: ", input_file_name, line_number) ==> fprintf (stderr, "%s:%d: " , input_file_name, line_number)
Within a `#define' directive, ISO C mandates that the only place
the identifier __VA_ARGS__
can appear is in the replacement list
of a variable-argument macro. It may not be used as a macro name, macro
argument name, or within a different type of macro. It may also be
forbidden in open text; the standard is ambiguous. We recommend you
avoid using it except for its defined purpose.
<Çؼ® Àß ¾ÈµÊ>
`#define' Áö½Ã¹® ³»¿¡¼, __VA_ARGS__ ½Äº°ÀÚ°¡ ³ªÅ¸³¯ ¼ö ÀÖ´Â °÷¿¡¼ÀÇ ISO C ¸í·ÉµéÀº °¡º¯ ÀÎÀÚ ¸ÅÅ©·Î ±³Ã¼ ¸®½ºÆ® ÀÌ´Ù. ¸ÅÅ©·Î À̸§, ¸ÅÅ©·Î ÀÎÀÚ À̸§À¸·Î½á »ç¿ë µÇÁö ¾ÊÀ» °ÍÀÌ´Ù. ¶ÇÇÑ ¿¸° ÅؽºÆ®¿¡¼ ±ÝÁö µÉ °ÍÀÌ´Ù. ¿ì¸®´Â ´ç½ÅÀÌ Á¤ÀÇ µÈ ¸ñÀû ÀÌ¿ÜÀÇ »ç¿ëÀ» ÇÇÇϱ⸦ ±ÇÀåÇÑ´Ù.
If your macro is complicated, you may want a more descriptive name for
the variable argument than __VA_ARGS__
. GNU cpp permits this, as
an extension. You may write an argument name immediately before the
`...'; that name is used for the variable argument. The
eprintf
macro above could be written
¸¸¾à ´ç½ÅÀÇ ¸ÅÅ©·Î°¡ º¹ÀâÇØÁö¸é, ´ç½ÅÀº __VA_ARGS__º¸´Ù °¡º¯ ÀÎÀÚ¸¦ À§ÇØ Á» ´õ ¼³¸íÀûÀÎ À̸§À» ¿øÇÒ ¼ö ÀÖµð. GNU cpp´ÂÀÌ°ÍÀÌ ÀÖ´Â ÀÌ°Í¿¡ È®ÀåÀ» Çã¶ôÇÑ´Ù. ´ç½ÅÀº `...' Àü¿¡ ¹Ù·Î ÀÎÀÚ À̸§À» ¾µ ¼ö ÀÖ´Ù; ±× À̸§Àº °¡º¯ ÀÎÀÚ¸¦ À§ÇØ »ç¿ë µÈ´Ù. eprintf ¸ÅÅ©·Î À§¿¡ ¾²¿© Áú ¼ö ÀÖ¾ú´Ù.
#define eprintf(args...) fprintf (stderr, args)
using this extension. You cannot use __VA_ARGS__
and this
extension in the same macro.
ÀÌ È®ÀåÀ» ÀÌ¿ëÇÑ´Ù. ´ç½ÅÀº __VA_ARGS__°ú ÀÌ È®ÀåÀ» °°Àº ¸ÅÅ©·Î¿¡¼ »ç¿ë ÇÒ ¼ö ¾ø´Ù.
We might instead have defined eprintf as follows:
¿ì¸®´Â ´ë½Å eprintf¸¦ ´ÙÀ½°ú °°ÀÌ Á¤ÀÇ ÇØ ¿ÔÀ» °ÍÀÌ´Ù.
#define eprintf(format, ...) fprintf (stderr, format, __VA_ARGS__)
This formulation looks more descriptive, but cannot be used as flexibly. There is no way to produce expanded output of
ÀÌ °ø½ÄÀº Á»´õ ¼³¸íÀûÀ¸·Î º¸ÀÌÁö¸¸ À¯¿¬ÇÏ°Ô ¾²ÀÏ ¼ö ¾ø´Ù. È®ÀåµÈ Ãâ·ÂÀ» ¸¸µé ¹æ¹ýÀÌ ¾ø´Ù.
fprintf (stderr, "success!\n")
because, in standard C, you are not allowed to leave the variable argument out entirely, and passing an empty argument for the variable arguments will not do what you want. Writing
¿Ö³ÄÇϸé Ç¥ÁØ C ´ë½Å¿¡ ´ç½ÅÀº ÀüüÀûÀ¸·Î °¡º¯ ÀÎÀÚµéÀ» ³²±â´Â °ÍÀ» Çã¶ôÇÏÁö ¾Ê´Â´Ù. ±×¸®°í °¡º¯ ÀÎÀÚµé·Î ¾Æ¹« ÀÎÀÚµµ ³Ñ°Ü ÁÖÁö ¾ÊÀ¸¸é ´ç½ÅÀÌ ¿øÇÏ´Â °ÍÀ» ÇÏÁö ¾ÊÀ» °ÍÀÌ´Ù.
eprintf ("success!\n", )
produces
fprintf (stderr, "success!\n",)
where the extra comma originates from the replacement list and not from the arguments to eprintf.
±³Ã¼ ¸®½ºÆ®·ÎºÎÅÍ ¿©ºÐÀÇ ÄÞ¸¶°¡ ¸¸µé¾î Áö°í ÀÎÀڵ鿡¼ºÎÅÍ eprintf±îÁö´Â ¾Æ´Ï´Ù.
There is another extension in the GNU C preprocessor which deals with this difficulty. First, you are allowed to leave the variable argument out entirely:
GNU CÀü󸮱⿡¼ È®ÀåÀ» ´Ù·ç´Â ´Ù¸¥ ¾î·Á¿òÀÌ ÀÖ´Ù. ¸ÕÀú, ´ç½ÅÀÌ ÀüüÀûÀ¸·Î ¹ÛÀÇ °¡º¯ ÀÎÀÚµéÀ» »ý·«ÇÏ´Â °ÍÀ» Çã¶ôÇÑ´Ù.
eprintf ("success!\n")
Second, the `##' token paste operator has a special meaning when placed between a comma and a variable argument. If you write
µÎ ¹ø°·Î, `##'ÅäÅ«Àº º¹»ç ¿¬»êÀÚ´Â ÄÞ¸¶¿Í °¡º¯ ÀÎÀÚ »çÀÌ¿¡ À§Ä¡ÇÒ ¶§ Ưº°ÇÑ Àǹ̸¦ °®´Â´Ù. ¸¸¾à ´ç½ÅÀÌ ¾Æ·¡¿Í °°ÀÌ ¾²¸é
#define eprintf(format, ...) fprintf (stderr, format, ##__VA_ARGS__)
and the variable argument is left out when the `eprintf' macro is used, then the comma before the `##' will be deleted. This does not happen if you pass an empty argument, nor does it happen if the token preceding `##' is anything other than a comma.
°¡º¯ ÀÎÀÚ´Â eprintf ¸ÅÅ©·Î°¡ »ç¿ëµÉ ¶§ »ý·«µÇ°í, ±× ´ÙÀ½¿£ ## Àü¿¡ ÄÞ¸¶´Â »èÁ¦µÉ °ÍÀÌ´Ù. ¸¸¾à ´ç½ÅÀÌ ºñ¾î ÀÖ´Â ÀÎÀÚ¸¦ ³Ñ±ä´Ù¸é ÀÌ°ÍÀº ¿ì¿¬È÷ ³ªÅ¸³ªÁö ¾Ê°í ±×°ÍÀº ¸¸¾à '##'À» ¼±ÇàÇÑ ÅäÅ«ÀÌ ÄÞ¸¶°¡ ¾Æ´Ñ ¾î¶² °ÍÀÌ´õ¶óµµ ¹ß»ýÇÏÁö ¾Ê´Â´Ù.
Previous versions of the preprocessor implemented this extension much more generally. We have restricted it in order to minimize the difference from the C standard. See section Undefined Behavior and Deprecated Features.
ÀÌÀü Àü󸮱⠹öÀüµéÀº Á»´õ ÀϹÝÀûÀ¸·Î ÀÌ È®ÀåÀ» ´Ù·ç ¾ú´Ù. ¿ì¸®´Â C Ç¥ÁØ°úÀÇ Â÷ÀÌÁ¡À» ÃÖ¼ÒÈÇϱâ À§ÇØ ±×°ÍÀ» Á¦ÇÑÇØ ¿Ô´Ù. Undefined Behavior and Deprecated FeaturesºÎºÐÀ» ºÁ¶ó
Several object-like macros are predefined; you use them without supplying their definitions. They fall into two classes: standard macros and system-specific macros.
¿©·¯ object-like ¸ÅÅ©·ÎµéÀº ÀÌ¹Ì Á¤ÀÇ µÇ¾î ÀÖ´Ù; ´ç½ÅÀº ±×µéÀÇ Á¤ÀÇ ¾øÀÌ »ç¿ëÇÒ ¼ö ÀÖ´Ù. ±×µéÀº µÎ °¡Áö ºÎ·ù·Î ³ª´«´Ù: Ç¥ÁØ ¸ÅÅ©·Î¿Í ½Ã½ºÅÛ ÁöÁ¤ ¸ÅÅ©·Î
The standard predefined macros are available with the same meanings
regardless of the machine or operating system on which you are using GNU
C. Their names all start and end with double underscores. Those
preceding __GNUC__
in this table are standardized by ISO C; the
rest are GNU C extensions.
¹Ì¸® Á¤ÀÇ µÈ Ç¥ÁØ ¸ÅÅ©·ÎµéÀº ´ç½ÅÀÌ GNU C¸¦ »ç¿ëÇÏ°í ÀÖ´Â ±â°è ¶Ç´Â ¿î¿µÃ¼Á¦¿¡ »ó°ü ¾øÀÌ ¸ðµÎ °°Àº Àǹ̷Π»ç¿ëÇÒ ¼ö ÀÖ´Ù. ±×µéÀÇ À̸§Àº ¸ðµç ½ÃÀÛ°ú ³¡ÀÌ µÎ°³ÀÇ ¾ð´õ½ºÄÚ¾î·Î µÇ¾î ÀÖ´Ù. __GNUC__°¡ Å×ÀÌºí¿¡¼ ¼±Çà µÇ¸é ISO C¿¡ ÀÇÇØ Ç¥ÁØÈ µÈ´Ù; ³ª¸ÓÁö´Â GNU C È®ÀåÀÌ´Ù.
__FILE__
ÀÌ ¸ÅÅ©·Î´Â C ¹®ÀÚ¿ »ó¼öÀÇ Çü½ÄÀ¸·Î ÇöÀç ÀÔ·Â ÆÄÀÏÀÇ À̸§À¸·Î È®Àå µÈ´Ù. ¹ÝȯµÈ Á¤È®ÇÑ À̸§Àº `#include'¿¡¼ ÁöÁ¤µÇ°Å³ª ÀÔ·Â ÆÄÀÏ À̸§ ÀÎÀڷνá ÁöÁ¤µÈ´Ù.
__LINE__
ÀÌ ¸ÅÅ©·Î´Â 10Áø Á¤¼öÀÇ ÇüÅ·ΠÇöÀç ÀÔ·Â ¶óÀÎÀÇ ¼ö·Î È®Àå µÈ´Ù. ¿ì¸®°¡ ¹Ì¸® Á¤ÀÇµÈ ¸ÅÅ©·Î¸¦ È£ÃâÇÏ´Â µ¿¾È ÀÌ°ÍÀº ²Ï ÀÌ»óÇÑ ¸ÅÅ©·Î ÀÌ´Ù. ¿Ö³ÄÇÏ¸é ±×°ÍÀÇ "Á¤ÀÇ"´Â ¼Ò½º ÄÚµåÀÇ °¢ »õ·Î¿î ¶óÀÎÀ¸·Î ¹Ù²î±â ¶§¹®ÀÌ´Ù. ÀÌ°Í°ú `__FILE__'Àº ÇÁ·Î±×·¥¿¡¼ ã¾Æ Áö´Â ºÒÀÏÄ¡¸¦ º¸°íÇÏ´Â ¿¡·¯ ¸Þ½ÃÁö¸¦ ¸¸µå´Âµ¥ À¯¿ëÇÏ´Ù; ±× ¸Þ½ÃÁö´Â ÀÏÄ¡ÇÏÁö ¾Ê´Â ¼Ò½º ¶óÀÎÀ» ã¾Æ¼ ³ªÅ¸³¾ ¼ö ÀÖ´Ù.
fprintf (stderr, "Internal error: " "negative string length " "%d at %s, line %d.", length, __FILE__, __LINE__);A `#include' directive changes the expansions of `__FILE__' and `__LINE__' to correspond to the included file. At the end of that file, when processing resumes on the input file that contained the `#include' directive, the expansions of `__FILE__' and `__LINE__' revert to the values they had before the `#include' (but `__LINE__' is then incremented by one as processing moves to the line after the `#include'). The expansions of both `__FILE__' and `__LINE__' are altered if a `#line' directive is used. See section Combining Source Files.
'#include' Áö½Ã¹®Àº Æ÷ÇÔµÈ ÆÄÀÏ¿¡ ºÎÇÕÇϱâ À§ÇÏ¿© '__FILE__' ±×¸®°í '__LINE__'ÀÇ È®ÀåµéÀ» ¹Ù²Û´Ù. ±× ÆÄÀÏÀÇ ³¡¿¡¼ `#include' Áö½Ã¹®À» ´ã°í ÀÖ´Â ÀÔ·Â ÆÄÀÏÀÇ Ã³¸®°¡ Àç°³µÉ ¶§, `__FILE__'°ú `__LINE__'È®ÀåÀº `#include'Àü¿¡ °ªµé·Î º¹±ÍµÈ´Ù.(±×·¯³ª `__LINE__¡¯Àº ´ÙÀ½¿¡ `#include¡¯ µÚ¿¡ ¶óÀÎÀ¸·Î 󸮰¡ ¿òÁ÷ÀÓÀ¸·Î½á Çϳª°¡ Áõ°¡ µÈ´Ù). `__FILE__' °ú `__LINE__' È®Àå ¸ðµÎ `#line¡¯Áö½Ã¹®ÀÌ »ç¿ëµÇ¸é ¹Ù²ï´Ù. Combining Source Files. ºÎºÐÀ» ºÁ¶ó
__DATE__
ÀÌ ¸ÅÅ©·Î´Â Àü󸮱⠽ÇÇàÀÌ ½ÃÀ۵Ǵ ³¯Â¥¸¦ ¼³¸íÇÏ´Â ¹®ÀÚ¿ »ó¼ö·Î È®Àå µÈ´Ù. ¹®ÀÚ¿ »ó¼ö´Â 11°³ ¹®ÀÚµéÀ» Æ÷ÇÔÇÏ°í `"Feb 1 1996"'°ú °°´Ù
__TIME__
ÀÌ ¸ÅÅ©·Î´Â Àü󸮱Ⱑ ½ÇÇàµÇ±â ½ÃÀÛÇÑ ½Ã°£À» ¼³¸íÇÏ´Â ¹®ÀÚ¿ »ó¼ö·Î È®Àå µÈ´Ù. ¹®ÀÚ¿ »ó¼ö´Â 8°³ÀÇ ¹®ÀÚ¸¦ Æ÷ÇÔÇÏ°í `"23:59:01"'°ú °°´Ù.
__STDC__
ÀÌ ¸ÅÅ©·Î´Â ISO Ç¥ÁØ C¿¡¼ ÀǹÌÇÏ´Â »ó¼ö 1·Î È®Àå µÈ´Ù.( ½ÇÁ¦·Î C ÄÄÆÄÀÏ·¯°¡ Àü󸮱âÀÇ Ãâ·ÂÀ» ¿î¿µÇÏ´Â °Í¿¡ ÀÇÁ¸ÇÏ´Â °ÍÀÌ »ç½ÇÀÌ´Ù) ¾î¶² È£½ºÆ®µé¿¡¼´Â ½Ã½ºÅÛÀÌ ´Ù¸¥ °ü·Ê·Î¼ `__STDC__'°¡ 0ÀÎ ÆÄÀϵéÀ» Æ÷ÇÔÇÏÁö¸¸ Ç¥ÁØ C¿¡ ¾ö°ÝÇÏ°Ô µû¶ó¿Â À¯Àú¶ó¸é 1·Î È®Àå ÇÒ °ÍÀÌ´Ù. Àü󸮱â´Â ó¸® ½Ã½ºÅÛÀÌ ÆÄÀϵéÀ» Æ÷ÇÔÇÒ ¶§ È£½ºÆ® °ü·Ê¸¦ µû¸£Áö¸¸ ó¸® À¯Àú ÆÄÀϵéÀº Ç×»ó GNU C °ü·Ê¸¦ µû¸¦ ¶§ È£½ºÆ®ÀÇ °ü·Ê¸¦ µû¸¥´Ù. ÀÌ ¸ÅÅ©·Î´Â `-traditional' ¿É¼ÇÀÇ »ç¿ëÀ¸·Î Á¤ÀÇ µÇÁö ¾Ê´Â´Ù.
__STDC_VERSION__
ÀÌ ¸ÅÅ©·Î´Â C Ç¥ÁØ ¹öÀüÀÇ ¼ýÀÚ·Î È®Àå µÈ´Ù. `yyyymmL`ÀÇ Çü½ÄÀÎlong interger »ó¼öÀÌ´Ù. yyyy¿Í mmÀº Ç¥ÁØ ¹öÀüÀÇ ³â°ú ´ÞÀÌ´Ù. ÀÌ°ÍÀº C Ç¥ÁØ Àü󸮱⿡ ¸Â´Â ¹öÀüÀ» ÀǹÌÇÑ´Ù. `__STDC__¡¯Ã³·³ Àü󸮱â·Î ºÎÅÍÀÇ Ãâ·ÂÀ» ¿î¿µÇÒ C ÄÄÆÄÀÏ·¯¿¡ ÀÇÁ¸Çؼ Àüü ¼öÇàÀÌ Á¤È®ÇÒ Áö ¾ÊÀ» Áö ¸ð¸¥´Ù.
__GNUC__
ÀÌ ¸ÅÅ©·Î´Â ÀÌ°ÍÀÌ GNU CÀ̸é Á¤ÀÇ µÈ´Ù. ÀÌ ¸ÅÅ©·Î´Â Àüü GNU C ÄÄÆÄÀÏ·¯°¡ »ç¿ë µÉ ¶§¸¸ Á¤ÀÇ µÈ´Ù; ¸¸¾à ´ç½ÅÀÌ Á÷Á¢ÀûÀ¸·Î Àü󸮱⸦ È£Ãâ Çϸé, `__GNUC__'´Â Á¤ÀÇ µÇÁö ¾Ê´Â´Ù. ±× °ªÀÌ GNU CCÀÇ ¸ÞÀÌÀú ¹öÀüÀ» È®ÀÎ ÇÑ´Ù.(`1' Àº Áö±ÝÀº ¾È ¾²ÀÌ´Â GNU CC ¹öÀü 1ÀÌ°í `2'´Â ¹öÀü 2ÀÌ´Ù)
__GNUC_MINOR__
__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 6)
).
¸ÅÅ©·Î´Â ÄÄÆÄÀÏ·¯ÀÇ ¸¶ÀÌ³Ê ¹öÀü ¼ýÀÚ¸¦ ´ã°í ÀÖ´Ù. ÀÌ°ÍÀº ÄÄÆÄÀÏ·¯ÀÇ ´Ù¸¥ ¹öÀü »çÀÌÀÇ Â÷À̸¦ ³ªÅ¸³¾ ¶§ »ç¿ë µÉ ¼ö ÀÖ´Ù(¿¹¸¦ µé¾î, Áö¿øµÇ´Â ÇüÅ°¡ GCC 2.6.3ÀÌ¸é ´ç½ÅÀº __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 6)¸¦ Å×½ºÆ® ÇÒ ¼ö ÀÖ´Ù.
__GNUC_PATCHLEVEL__
__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ > 6) ||
(__GNUC__ == 2 && __GNUC_MINOR__ == 6 && __GNUC_PATCHLEVEL__ > 3)
).
ÀÌ ¸ÅÅ©·Î´Â ÄÄÆÄÀÏ·¯ÀÇ ÆÐÄ¡ ´Ü°è¸¦ ´ã°í ÀÖ´Ù. ÀÌ°ÍÀº ÄÄÆÄÀÏ·¯ÀÇ ´Ù¸¥ ÆÐÄ¡ ´Ü°è ¹èÆ÷»çÀÌÀÇ Â÷À̵éÀ» ³ªÅ¸³»´Âµ¥ »ç¿ë µÉ ¼ö ÀÖ´Ù. ( ¿¹¸¦ µé¸é ¸¸¾à GCC 2.6.2°¡ ¹ö±×¸¦ ´ã°í ÀÖ´Ù°í ¾Ë·ÁÁö°í GCC 2.6.3°¡ ¼öÁ¤ µÈ °ÍÀ» ´ã°í ÀÖÀ¸¸é ´ç½ÅÀº ¹ö±×°¡ ¼öÁ¤ µÆ´ÂÁö ¾È µÆ´ÂÁö¿¡ µû¶ó ¹®Á¦¸¦ ³ªÅ¸³»´Â Äڵ带 °¡Áö°í ÀÖ´Â Áö¸¦ Å×½ºÆ® ÇÒ ¼ö ÀÖ´Ù. __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ > 6) || (__GNUC__ == 2 && __GNUC_MINOR__ == 6 && __GNUC_PATCHLEVEL__ > 3)).
__GNUG__
GNU C ÄÄÆÄÀÏ·¯´Â ÄÄÆÄÀÏ ¾ð¾î°¡ C++ÀÏ ¶§ ÀÌ°ÍÀ» Á¤ÀÇ ÇÑ´Ù; GNU C¿Í GNU C++ ¸¦ ±¸º°Çϱâ À§ÇØ '__GNUG__'À» »ç¿ëÇضó
__cplusplus
C++¸¦ À§ÇÑ ISO Ç¥ÁØÀº ÀÌ º¯¼ö¸¦ ¹Ì¸® Á¤ÀÇÇÏ´Â °ÍÀ» ¿ä±¸ ÇÑ´Ù. ´ç½ÅÀº Çì´õ°¡ CÄÄÆÄÀÏ·¯·Î ÄÄÆÄÀÏ µÇ´ÂÁö C++ÄÄÆÄÀÏ·¯·Î ÄÄÆÄÀÏ µÇ´ÂÁö Å×½ºÆ®¸¦ À§ÇØ `__cplusplus'¸¦ »ç¿ë ÇÒ ¼ö ÀÖ´Ù. ÇöÀç ÄÄÆÄÀÏ·¯´Â `199711L'´ë½Å¿¡ ¿ÏÀüÇÑ ÀÏÄ¡¸¦ °¡¸£Å°´Â `1' °ªÀ» »ç¿ëÇÑ´Ù.
__STRICT_ANSI__
GNU C¸¦ È£Ãâ ÇßÀ» ¶§ `-ansi¡¯ ½ºÀ§Ä¡°¡ ÁöÁ¤µÇ¾î ÀÖ¾î¾ß¸¸ GNU C´Â ÀÌ ¸ÅÅ©·Î¸¦ Á¤ÀÇÇÑ´Ù. ÀÌ ¸ÅÅ©·Î´Â ¿ì¼±ÀûÀ¸·Î ISO C¿Í ÇÔ²² ÇÒ ¼ö ¾ø´Â ÀüÅëÀû UNIX ±¸Á¶°¡ ¾Æ´Ñ ¾î¶²GNU Çì´õÆÄÀϵéÀ» Áö½ÃÇÏ´Â Çϱâ À§ÇØ Á¸ÀçÇÑ´Ù.
__BASE_FILE__
ÀÌ ¸ÅÅ©·Î´Â C ¹®ÀÚ¿ »ó¼ö ÇüÅ·ΠÁÖ ÀÔ·Â ÆÄÀÏÀÇ À̸§À» È®ÀåÇÑ´Ù. ÀÌ°ÍÀº Àü󸮱â¿Í C ÄÄÆÄÀÏ·¯ÀÇ ¸í·É¶óÀο¡ ÁöÁ¤µÈ ¼Ò½ºÀÌ´Ù.
__INCLUDE_LEVEL__
ÀÌ ¸ÅÅ©·Î´Â include ÆÄÀϵ鿡¼ nestingÀÇ ±íÀ̸¦ ³ªÅ¸³»´Â 10Áø Á¤¼öÇü »ó¼ö·Î È®Àå µÈ´Ù. ÀÌ ¸ÅÅ©·ÎÀÇ °ªÀº ¸Å¹ø `#include¡¯Áö½Ã¹®¿¡¼ Áõ°¡ÇÏ°í ¸Å¹ø includeµÈ ÆÄÀÏÀÇ ³¡¿¡¼ °¨¼Ò µÈ´Ù. 0¿¡¼ ½ÃÀÛÇÏ°í ¸í·É ¶óÀο¡ ÁöÁ¤µÈ ±âº» ÆÄÀÏ ¾ÈÀÇ °ªÀÌ´Ù.
__VERSION__
ÀÌ ¸ÅÅ©·Î´Â GNU CÀÇ ¹öÀü ¼ýÀÚ¸¦ ¼³¸íÇϱâ À§ÇÑ ¹®ÀÚ¿ »ó¼ö·Î È®Àå µÈ´Ù. ¹®ÀÚ¿Àº º¸Åë ¸¶Ä§Ç¥·Î ºÐ¸®µÈ 10Áø ¼ýÀÚµéÀÇ ³ª¿ÀÌ´Ù.
__OPTIMIZE__
GNU CC´Â ÃÖÀûÈ ÄÄÆÄÀÏ¿¡ ÀÌ ¸ÅÅ©·Î¸¦ Á¤ÀÇ ÇÑ´Ù. ¸î¸îÀÇ ½Ã½ºÅÛ ¶óÀ̺귯¸® ÇÔ¼öµéÀ» À§ÇÑ ´ë¾ÈÀÎ ¸ÅÅ©·Î¸¦ Á¤ÀÇ ÇÏ´Â °ÍÀº ¾î¶² GNU Çì´õ ÆÄÀϵéÀÇ ¿øÀÎÀÌ µÈ´Ù. ´ç½ÅÀÌ °í·ÁÇÏÁö ¾ÊÀ» ¸¸Å °°Àº È¿°ú·Î ÇÁ·Î±×·¥ÀÌ ½ÇÇà µÉ °ÍÀ» Á¤¸»·Î È®½ÇÇÒ ¼ö ÀÖÁö ¾ÊÀ¸¸é ÀÌ ¸ÅÅ©·ÎÀÇ Á¤ÀǸ¦ Å×½ºÆ®Çϰųª »ý°¢ÇÏÁö ¸»¾Æ¶ó
__CHAR_UNSIGNED__
char
is
unsigned on the target machine. It exists to cause the standard header
file `limits.h' to work correctly. You should not refer to this
macro yourself; instead, refer to the standard macros defined in
`limits.h'. The preprocessor uses this macro to determine whether
or not to sign-extend large character constants written in octal; see
section The `#if' Directive.
GNU C´Â µ¥ÀÌÅÍ Å¸ÀÔ char°¡ ¸Ó½Å¿¡¼ ºÎÈ£¸¦ °®Áö ¾ÊÀ¸¸é ÀÌ ¸ÅÅ©·Î¸¦ Á¤ÀÇ ÇÑ´Ù. Á¤È®ÇÏ°Ô ÀÛµ¿Çϱâ À§ÇÑ Ç¥ÁØ Çì´õ ÆÄÀÏ `limits.h' ¿¡¼ Á¸Àç ÇÑ´Ù.´ç½ÅÀº ´ç½Å ½º½º·Î ÀÌ ¸ÅÅ©·Î¸¦ »ý°¢ÇÏÁö ¾Ê¾Æ¾ß¸¸ ÇÑ´Ù; ´ë½Å, `limits.h'¿¡ Á¤ÀÇ µÈ Ç¥ÁØ ¸ÅÅ©·Î·Î ¿©°Ü¶ó. Àü󸮱â´Â 8Áø¼ö·Î ¾²¿©Áøsign-extend Å« ¹®ÀÚ »ó¼ö ÀÎÁö ¾Æ´ÑÁö °áÁ¤Çϱâ À§ÇØ ÀÌ ¸ÅÅ©·Î¸¦ »ç¿ëÇÑ´Ù. The `#if' Directive¸¦ ºÁ¶ó
__REGISTER_PREFIX__
ÀÌ ¸ÅÅ©·Î´Â ¾î¼Àºí¸® Äڵ忡¼ CPU ·¹Áö½ºÅ͵é·Î ¹Þ¾Æ µé¿©Áø Á¢µÎ¾î¸¦ ¼³¸íÇÏ´Â ¹®ÀÚ¿(¹®ÀÚ¿ »ó¼ö°¡ ¾Æ´Ñ)·Î È®Àå µÈ´Ù. ´ç½ÅÀº ´ÙÁß È¯°æ¿¡¼ »ç¿ë µÉ ¼ö ÀÖ´Â ¾î¼Àºí·¯ Äڵ带 ¾²±â À§ÇØ ±×°ÍÀ» »ç¿ëÇÒ ¼ö ÀÖ´Ù. ¿¹¸¦ µé¾î, `m68k-aout'ȯ°æ¿¡¼ ³Î ¹®ÀÚ¿·Î È®Àå µÇÁö¸¸ `m68k-coff'ȯ°æ¿¡¼´Â `%'·Î È®ÀåµÈ´Ù.
__USER_LABEL_PREFIX__
__REGISTER_PREFIX__
, but describes the prefix applied
to user generated labels in assembler code. For example, in the
`m68k-aout' environment it expands to the string `_', but in
the `m68k-coff' environment it expands to the null string. This
does not work with the `-mno-underscores' option that the i386
OSF/rose and m88k targets provide nor with the `-mcall*' options of
the rs6000 System V Release 4 target.
__REGISTER_PREFIX__¿Í ºñ½ÁÇÏÁö¸¸ ¾î¼Àºí¸® Äڵ忡¼ À¯Àú°¡ »ý¼ºÇÑ ¶óº§µé·Î ¹Þ¾Æ µé¿©Áø Á¢µÎ¾î¸¦ ¼³¸íÇÑ´Ù. ¿¹¸¦ µé¾î, `m68k-aout'ȯ°æ¿¡¼ ±×°ÍÀº ¹®ÀÚ¿`_'·Î È®ÀåµÇÁö¸¸ `m68k-coff' ȯ°æ¿¡¼´Â ³Î ¹®ÀÚ¿·Î È®ÀåµÈ´Ù. ÀÌ°ÍÀº i386 OSF/rose¿Í m88k°¡ ¸ñÇ¥ÇÑ `-mno- unerscores' ¿É¼ÇÀ¸·Î ÀÛµ¿ÇÏÁö ¾Ê°í ¶ÇÇÑ rs6000 System V Release 4¸¦ ¸ñÇ¥·Î ÇÑ ¿É¼Çµµ ¾Æ´Ï´Ù.
The C preprocessor normally has several predefined macros that vary between machines because their purpose is to indicate what type of system and machine is in use. This manual, being for all systems and machines, cannot tell you exactly what their names are; instead, we offer a list of some typical ones. You can use `cpp -dM' to see the values of predefined macros; see section Invoking the C Preprocessor.
C Àü󸮱â´Â º¸Åë ¿©·¯ °³ÀÇ ¹Ì¸® Á¤ÀÇµÈ ¸Ó½Å »çÀÌ¿¡¼ ´Ù¾çÇÑ ¸ÅÅ©·Î¸¦ °¡Áø´Ù. ¿Ö³ÄÇÏ¸é ±×µéÀÇ ¸ñÀûÀº »ç¿ëµÇ´Â ½Ã½ºÅÛ°ú ¸Ó½Å »çÀÌÀÇ Å¸ÀÔÀÌ ¹«¾ùÀÎÁö¸¦ °¡¸®Å°±â À§Çؼ ÀÌ´Ù. ÀÌ ¼³¸í¼¿¡¼´Â ¸ðµç ½Ã½ºÅÛµé°ú ¸Ó½Åµé¿¡¼ Á¸ÀçÇÏ´Â ±×µéÀÇ À̸§µéÀÌ ¹«¾ùÀÎÁö´Â Á¤È®ÇÏ°Ô ¸»ÇØ ÁÙ ¼ö ¾ø´Ù; ´ë½Å ¿ì¸®´Â ¸î¸îÀÇ ÀüÇüÀûÀÎ °ÍµéÀÇ ¸®½ºÆ®¸¦ Á¦°ø ÇÑ´Ù. ´ç½ÅÀº ¹Ì¸® Á¤ÀÇµÈ ¸ÅÅ©·Î °ªÀ» º¸±â À§ÇØ`cpp -dM'¸¦ »ç¿ëÇÒ ¼ö ÀÖ´Ù; Invoking the C Preprocessor ºÎºÐÀ» ºÁ¶ó
Some nonstandard predefined macros describe the operating system in use, with more or less specificity. For example,
¸î¸îÀÇ ºñÇ¥ÁØÀ¸·Î ¹Ì¸® Á¤ÀÇ µÈ ¸ÅÅ©·ÎµéÀº ¾²ÀÌ°í ÀÖ´Â ¿î¿µÃ¼Á¦ÀÇ Æ¯¼ºÀ» ¸¹°Å³ª Àû°Ô ¼³¸íÇÑ´Ù.
unix
`unix'´Â º¸Åë ¸ðµç À¯´Ð½º ½Ã½ºÅ۵鿡¼ ¹Ì¸® Á¤ÀÇ µÇ¾î ÀÖ´Ù.
BSD
`BSD'´Â ÃÖ±Ù ¹öŬ¸® À¯´Ð½º ¹öÀü¿¡ ¹Ì¸® Á¤ÀÇ µÇ¾îÀÖ´Ù (¾Æ¸¶µµ version 4.3¿¡¼¸¸)
Other nonstandard predefined macros describe the kind of CPU, with more or less specificity. For example,
´Ù¸¥ ºñÇ¥ÁØÀ¸·Î ¹Ì¸® Á¤ÀÇ µÈ ¸ÅÅ©·ÎµéÀº ¿©·¯ Á¾·ùÀÇ CPUÀÇ Æ¯¼ºÀ» ¸¹°Å³ª Àû°Ô ¼³¸íÇÑ´Ù.
vax
`vax'´Â Vax ÄÄÇ»Å͵鿡 ¹Ì¸® Á¤ÀÇ µÇ¾î ÀÖ´Ù
mc68000
`mc68000'Àº CPU°¡ Motorola 68000, 68010 ȤÀº 68020ÀÎ ´ëºÎºÐÀÇ ÄÄÇ»Å͵鿡 ¹Ì¸® Á¤ÀÇ µÇ¾î ÀÖ´Ù.
m68k
`m68k¡¯¶ÇÇÑ CPU°¡ 68000, 68010 ȤÀº 68020ÀÎ ´ëºÎºÐÀÇ ÄÄÇ»Å͵鿡¼ ¹Ì¸® Á¤ÀÇ µÇ¾î ÀÖ´Ù. ±×·¯³ª ¸î¸î »óÇ¥µéÀº `mc68000¡¯À» »ç¿ëÇÏ°í ¸î¸îÀº `m68k¡¯¸¦ »ç¿ëÇÑ°í ¸î¸îÀº µÑ´Ù »ç¿ëÇÑ´Ù.GNU C¿¡¼ ¹ß»ýÇÏ´Â °ÍÀº ´ç½ÅÀÌ »ç¿ë ÁßÀÎ ½Ã½ºÅÛ¿¡ ÀÇÁ¸ÇÑ´Ù.
M68020
`M68020'Àº 68020 CPUµéÀ» »ç¿ëÇÏ´Â ¸î¸î ½Ã½ºÅ۵鿡 ¹Ì¸® Á¤ÀÇ µÇ¾î ÀÖ´Â °ÍÀ¸·Î °üÂû µÇ¾î ¿Ô´Ù.-µ¡ºÙ¿© `mc68000'°ú `m68k'´Â ´ú ±¸Ã¼ÀûÀÌ´Ù.
_AM29K
_AM29000
`_AM29K' ±×¸®°í `_AM29000' µÑ´Ù AMD 29000 CPU ½Ã¸®Á À§ÇØ ¹Ì¸® Á¤ÀÇ µÇ¾î ÀÖ´Ù.
ns32000
`ns32000'Àº the National Semiconductor 32000 series CPU¸¦ »ç¿ëÇÏ´Â ÄÄÇ»Å͵鿡 ¹Ì¸® Á¤ÀÇ µÇ¾î ÀÖ´Ù.
Yet other nonstandard predefined macros describe the manufacturer of the system. For example,
¾ÆÁ÷ ´Ù¸¥ ºñÇ¥ÁØÀ¸·Î ¹Ì¸® Á¤ÀÇµÈ ¸ÅÅ©·ÎµéÀº ½Ã½ºÅÛÀÇ È¸»ç¸íÀ¸·Î ¼³¸íÇÑ´Ù. ¿¹¸¦ µé¸é,
sun
Sun ÄÄÇ»Å͵éÀÇ ¸ðµç ¸ðµ¨µéÀ» `sun'À¸·Î ¹Ì¸® Á¤ÀÇ µÈ´Ù.
pyr
`pyr'´Â Pyramid ÄÄÇ»Å͵éÀÇ ¸ðµç ¸ðµ¨¿¡¼ ¹Ì¸® Á¤ÀÇ µÈ´Ù
sequent
`sequent'´Â Sequent ÄÄÇ»Å͵éÀÇ ¸ðµç ¸ðµ¨¿¡¼ ¹Ì¸® Á¤ÀÇ µÈ´Ù.
These predefined symbols are not only nonstandard, they are contrary to the ISO standard because their names do not start with underscores. Therefore, the option `-ansi' inhibits the definition of these symbols.
¹Ì¸® Á¤ÀÇ µÈ ½É¹úµéÀº ºñÇ¥ÁØÀÏ »Ó¸¸ ¾Æ´Ï¶ó ISOÇ¥ÁØ¿¡ ÀûÇÕÇÏÁö ¾Ê´Ù. ¿Ö³ÄÇÏ¸é ±×µéÀÇ À̸§Àº ¾ð´õ½ºÄÚ¾î·Î ½ÃÀÛÇÏÁö ¾Ê´Â´Ù. ±×·¯¹Ç·Î, `-ansi'¿É¼ÇÀº ÀÌ ½É¹úµéÀÇ Á¤ÀǸ¦ ¸øÇÏ°Ô ÇÑ´Ù.
This tends to make `-ansi' useless, since many programs depend on the customary nonstandard predefined symbols. Even system header files check them and will generate incorrect declarations if they do not find the names that are expected. You might think that the header files supplied for the Uglix computer would not need to test what machine they are running on, because they can simply assume it is the Uglix; but often they do, and they do so using the customary names. As a result, very few C programs will compile with `-ansi'. We intend to avoid such problems on the GNU system.
¸¹Àº ÇÁ·Î±×·¥µéÀÌ °ü·ÊÀûÀÎ ºñÇ¥ÁØÀ¸·Î Á¤ÀÇµÈ ½É¹úµé¿¡ ÀÇÁ¸Çϱ⠶§¹®¿¡ `-ansi' ¿É¼ÇÀ» ¾µ¸ð ¾ø°Ô Çϱ⠽±´Ù. ½Ã½ºÅÛ ÆÄÀϵéÀÌ ±×°ÍµéÀ» üũÇÏÁö¸¸ ¿¹»óÇÑ À̸§À» ãÁö ¸øÇϸé Á¤È®ÇÏÁö ¾ÊÀº ¼±¾ðÀÌ ¹ß»ý ÇÒ ¼ö ÀÖ´Ù. ´ç½ÅÀº Uglix ÄÄÇ»ÅÍ¿¡ Á¦°ø µÇ´Â Çì´õ ÆÄÀϵéÀº ¸Ó½Å¿¡¼ ÀÛµ¿ÇÏ´ÂÁö¸¦ Å×½ºÆ® ÇÒ ÇÊ¿ä°¡ ¾ø´Ù°í »ý°¢ÇÒ ¸ð¸¥´Ù. ¿Ö³ÄÇϸé Çì´õÆÄÀϵéÀº ½±°Ô ±×°ÍÀÌ Uglix¶ó°í »ý°¢ ÇÒ ¼ö Àֱ⠶§¹®ÀÌ´Ù; ±×·¯³ª ÀÚÁÖ ±×·¸°Ô ÇÏÁö¸¸ ±×°ÍµéÀº ¶ÇÇÑ ÀÚÁÖ °ü½ÀÀûÀÎ À̸§µé·Î »ç¿ë ÇÑ´Ù. ±× °á°ú ¸Å¿ì ÀûÀº C ÇÁ·Î±×·¥µéÀÌ `-ansi'·Î ÄÄÆÄÀÏ µÉ °ÍÀÌ´Ù. ¿ì¸®´Â GNU ½Ã½ºÅÛ¿¡¼ ±×·± ¹®Á¦¸¦ ÇÇÇÏ·Á°í ÇÑ´Ù.
What, then, should you do in an ISO C program to test the type of machine it will run on?
½ÇÇàµÉ ¸Ó½Å ŸÀÔÀ» Å×½ºÆ®Çϱâ À§ÇØ ISO C ÇÁ·Î±×·¥¿¡ ´ç½ÅÀº ¹«¾ùÀ» Çؾ߸¸ Çϴ°¡?
GNU C offers a parallel series of symbols for this purpose, whose names
are made from the customary ones by adding `__' at the beginning
and end. Thus, the symbol __vax__
would be available on a Vax,
and so on.
GNU C´Â ÀÌ ¸ñÀûÀ» À§ÇØ ½É¹úµéÀÇ º´·Ä ½Ã¸®ÁîµéÀ» Á¦°øÇÑ´Ù.º´·Ä ½Ã¸®ÁîµéÀº ½ÃÀÛ°ú ³¡¿¡ `__'À» ´õÇÔÀ¸·Î½á °ü·ÊÀûÀ¸·Î ¸¸µç´Ù.°Ô´Ù°¡ ½Éº¼ __vax__´Â Vax³ª ±× ¹Û¿¡ °Íµé·Î »ç¿ë µÈ´Ù.
The set of nonstandard predefined names in the GNU C preprocessor is
controlled (when cpp
is itself compiled) by the macro
`CPP_PREDEFINES', which should be a string containing `-D'
options, separated by spaces. For example, on the Sun 3, we use the
following definition:
ºñÇ¥ÁØÀ¸·Î ¹Ì¸® Á¤ÀÇ µÈ GNUÀü󸮱⿡ À̸§µéÀÇ ÁýÇÕÀº `CPP_PREDEFINES' ¸ÅÅ©·Î¿¡ ÀÇÇØ ÅëÁ¦(cpp°¡ ½º½º·Î ÄÄÆÄÀÏ µÉ ¶§) µÈ´Ù. ±×¸®°í `-D'¿É¼ÇÀ» Æ÷ÇÔÇÑ ¹®ÀÚ¿À̾î¾ß ÇÏ°í °ø°£À¸·Î ºÐ¸®µÇ¾î ÀÖ¾î¾ß ÇÑ´Ù. ¿¹¸¦ µé¸é Sun 3Àº ´ÙÀ½ÀÇ Á¤ÀǸ¦ µû¸¥´Ù.
#define CPP_PREDEFINES "-Dmc68000 -Dsun -Dunix -Dm68k"
This macro is usually specified in `tm.h'.
ÀÌ ¸ÅÅ©·Î´Â Ç×»ó `tm.h'¿¡ ÁöÁ¤µÈ´Ù.
Stringification means turning a sequence of preprocessing tokens into a string literal. For example, stringifying `foo (z)' results in `"foo (z)"'.
StringificationÀº Àüó¸® µÇ´Â ÅäÅ«µéÀÇ ¿ÀÌ ¹®ÀÚ¿ ±×´ë·Î ÀüȯµÇ´Â °ÍÀ» ÀǹÌÇÑ´Ù. ¿¹¸¦ µé¸é, stringigying `foo(z)'ÀÇ °á°ú´Â `"foo (z)"' ÀÌ´Ù.
In the C preprocessor, stringification is possible when macro arguments are substituted during macro expansion. When a parameter appears preceded by a `#' token in the replacement list of a function-like macro, it indicates that both tokens should be replaced with the stringification of the corresponding argument during expansion. The same argument may be substituted in other places in the definition without stringification if the argument name appears in those places with no preceding `#'.
C Àü󸮱⿡¼stringificationÀº ¸ÅÅ©·Î°¡ È®ÀåµÇ´Â µ¿¾È¿¡ ¸ÅÅ©·Î ÀÎÀÚµéÀÌ ´ëüµÉ ¶§ °¡´ÉÇÏ´Ù. ÆĶó¹ÌÅÍ°¡ function-like ¸ÅÅ©·ÎÀÇ ´ëü ¸®½ºÆ®¿¡¼ `#' ÅäÅ« º¸´Ù ¸ÕÀú ³ªÅ¸³¯ ¶§, ÅäÅ«µéÀÌ ¸ÅÅ©·Î°¡ È®ÀåÇÏ´Â µ¿¾È ÀÏÄ¡ÇÏ´Â ÀÎÀÚÀÇ stringifiationÀ¸·Î ¹Ù²î¾î¾ß ÇÏ´Â °ÍÀ» °¡¸£Å²´Ù. ÀÎÀÚ À̸§ÀÌ `#'ÀÌ ¼±Çà µÇÁö ¾Ê°í ±×·± °÷¿¡ ³ªÅ¸³´Ù¸é °°Àº ÀÎÀÚ´Â ´Ù¸¥ °÷¿¡¼ stringification ¾ø´Â Á¤ÀÇ·Î ´ëü µÉÁö ¸ð¸¥´Ù.
Here is an example of a macro definition that uses stringification:
stringificationÀ» ÀÌ¿ëÇÑ ¸ÅÅ©·Î Á¤ÀÇÀÇ ¿¹°¡ ¿©±â ÀÖ´Ù.
#define WARN_IF(EXP) \ do { if (EXP) \ fprintf (stderr, "Warning: " #EXP "\n"); } \ while (0)
Here the argument for `EXP' is substituted once, as-is, into the `if' statement, and once, stringified, into the argument to `fprintf'. The `do' and `while (0)' are a kludge to make it possible to write `WARN_IF (arg);', which the resemblance of `WARN_IF' to a function would make C programmers want to do; see section Swallowing the Semicolon.
¿©±â¼ ÀÎÀÚ ' EXP '´Â ÇÑ ¹ø `if' Áø¼ú·Î ġȯµÇ°í Çѹø `fprintf'¿¡ ÀÎÀÚ·Î stringified µÈ´Ù. `do'¿Í `while(0)'´Â `WARN_IF(arg);'¸¦ ¾²´Â °ÍÀ» °¡´ÉÇÏ°Ô ¸¸µå´Â ´Ù¼Ò ±ÍÂúÀº ¹®Á¦¿¡ ´ëÇÑ ÁÁÀº ÇØ°áÃ¥ÀÌ´Ù. ÇÔ¼ö¿Í À¯»çÇÑ `WARN_IF' Àº C ÇÁ·Î±×·¡¸Ó°¡ ÇÏ°í ½ÍÀº °ÍÀ» ¸¸µç´Ù.; Swallowing the Semicolon.¸¦ ºÁ¶ó
The stringification feature is limited to transforming the tokens of a macro argument into a string constant: there is no way to combine the argument with surrounding text and stringify it all together. The example above shows how an equivalent result can be obtained in ISO Standard C, using the fact that adjacent string constants are concatenated by the C compiler to form a single string constant. The preprocessor stringifies the actual value of `EXP' into a separate string constant, resulting in text like
stringification Ư¡Àº ¸ÅÅ©·Î ÀÎÀÚ ÅäÅ«µéÀ» ¹®ÀÚ¿ »ó¼ö·Î º¯È¯ÇÏ´Â °ÍÀÌ Á¦ÇÑ µÈ °ÍÀÌ´Ù.: ÅؽºÆ®·Î µÑ·¯ ½×ÀÎ ÀÎÀÚ¸¦ ÇÕÄ¡´Â °Í°ú ±×°ÍÀ» ¸ðµÎ ÇÔ²² ¹®ÀÚ¿·Î ¸¸µå´Â °ÍÀº ºÒ°¡´ÉÇÏ´Ù. À§ÀÇ ¿¹´Â ÀÎÁ¢ÇÑ ¹®ÀÚ¿ »ó¼öµéÀÌ C ÄÄÆÄÀÏ·¯¿¡ ÀÇÇØ ´ÜÀÏ ¹®ÀÚ¿ »ó¼ö ÇüÅ·Π¿¬°áµÇ´Â °ÍÀ» ÀÌ¿ëÇؼ ISO Ç¥ÁØ C¿¡¼ °°Àº °á°ú°¡ ¾î¶»°Ô ¾ò¾î Áú ¼ö ÀÖ´ÂÁö¸¦ º¸¿©ÁØ´Ù. Àü󸮱â´Â `EXP'ÀÇ ½ÇÁ¦ °ªÀ» ºÐ¸®µÈ ¹®ÀÚ¿ »ó¼ö·Î ¹®ÀÚ¿ÈÇÑ´Ù.
do { if (x == 0) \ fprintf (stderr, "Warning: " "x == 0" "\n"); } \ while (0)
but the compiler then sees three consecutive string constants and concatenates them into one, producing effectively
±×·¯³ª ÄÄÆÄÀÏ·¯´Â ¼¼ °³ÀÇ ¿¬¼ÓÀûÀÎ ¹®ÀÚ¿ »ó¼öµéÀ» º¸°í È¿°úÀûÀ¸·Î ±×°ÍµéÀ» Çϳª·Î ¿¬°áÇÑ´Ù.
do { if (x == 0) \ fprintf (stderr, "Warning: x == 0\n"); } \ while (0)
Stringification in C involves more than putting double-quote characters around the fragment. The preprocessor backslash-escapes the surrounding quotes of string literals, and all backslashes within string and character constants, in order to get a valid C string constant with the proper contents. Thus, stringifying `p = "foo\n";' results in `"p = \"foo\\n\";"'. However, backslashes that are not inside string or character constants are not duplicated: `\n' by itself stringifies to `"\n"'.
C¿¡¼ Stringification´Â ÆÄÆíµé ÁÖÀÇ¿¡ double-quote ¹®ÀÚµéÀ» ³õ´Â °ÍÀ» º¸´Ù ´õ Æ÷ÇÔÇÑ´Ù. backslash-escapes·Î µÑ·¯ ½×ÀÎ Àü󸮱â´Â ¹®ÀÚ¿ ±×´ë·Î ÀοëµÇ°í ¹®ÀÚ¿°ú ¹®ÀÚ »ó¼ö ³»¿¡¼ÀÇ ¹é½½·¡½¬µéµµ ÀοëµÈ´Ù. ÀÌ°ÍÀº ÀûÀýÇÑ ³»¿ë¿¡ Á¤´çÇÑ C¹®ÀÚ¿ »ó¼ö¸¦ ¾ò±â À§Çؼ ÀÌ´Ù. ±×·¯³ª, ¹®ÀÚ¿ ¶Ç´Â ¹®ÀÚµé ¾È¿¡ ¾ø´Â ¹é½½·¡½¬µéÀº Áߺ¹µÇÁö ¾Ê´Â´Ù: `\n'Àº ½º½º·Î `"\n"'·Î stringifies ÇÑ´Ù.
Whitespace (including comments) in the text being stringified is handled according to precise rules. All leading and trailing whitespace is ignored. Any sequence of whitespace in the middle of the text is converted to a single space in the stringified result.
¹®ÀÚ¿È µÈ ÅؽºÆ®¿¡ °ø¹é(ÁÖ¼®À» Æ÷ÇÔÇÑ)Àº Á¤È®ÇÑ ±ÔÄ¢¿¡ µû¶ó ´Ù·ç¾îÁø´Ù. ¸ðµç ¾Õ µÚ °ø¹éÀº ¹«½ÃµÈ´Ù. ÅؽºÆ® Áß°£¿¡ ¾î¶² °ø¹éÀÇ ¿µµ ¹®ÀÚ¿È µÈ °á°ú·Î ÇϳªÀÇ °ø°£À¸·Î ¹Ù²ï´Ù.
Concatenation means joining two strings into one. In the context of macro expansion, concatenation refers to joining two preprocessing tokens to form one. In particular, a token of a macro argument can be concatenated with another argument's token or with fixed text to produce a longer name. The longer name might be the name of a function, variable, type, or a C keyword; it might even be the name of another macro, in which case it will be expanded.
¿¬°áÀº µÎ°³ÀÇ ¹®ÀÚ¿À» Çϳª·Î °áÇÕ½ÃÅ°´Â °ÍÀ» ÀǹÌÇÑ´Ù. ¸ÅÅ©·Î È®Àå ³»¿ë¿¡¼ ¿¬°áÀº ÇϳªÀÇ ÇüÅ·ΠµÎ°³ÀÇ Àüó¸® ÅäÅ«µéÀ» °áÇÕ ½ÃÅ°´Â °ÍÀ¸·Î ¿©±ä´Ù. ƯÈ÷ ¸ÅÅ©·Î ÀÎÀÚ ÅäÅ«Àº ´Ù¸¥ ÀÎÀÚÀÇ ÅäÅ«À̳ª ´õ ±ä À̸§À» ¸¸µé±â À§ÇÑ °íÁ¤µÈ ÅؽºÆ®·Î ¿¬°á µÉ ¼ö ÀÖ´Ù. ´õ ±ä À̸§Àº ÇÔ¼ö, º¯¼ö, ŸÀÔ ¶Ç´Â C keyword°¡ µÉÁö ¸ð¸¥´Ù; ±×°ÍÀº È®ÀåµÇ¾îÁú °æ¿ì ´Ù¸¥ ¸ÅÅ©·ÎÀÇ À̸§ÀÌ µÉÁöµµ ¸ð¸¥´Ù.
When you define a function-like or object-like macro, you request concatenation with the special operator `##' in the macro's replacement list. When the macro is called, any arguments are substituted without performing macro expansion, every `##' operator is deleted, and the two tokens on either side of it are concatenated to form a single token.
´ç½ÅÀÌ function-like³ª object-like ¸ÅÅ©·Î¸¦ Á¤ÀÇ ÇÒ ¶§ ¸ÅÅ©·ÎÀÇ ±³Ã¼ ¸ñ·Ï¿¡¼ Ưº°ÇÑ`##' ¿¬»êÀÚ·Î ¿¬°áÀ» ¿äûÇÑ´Ù. ¸ÅÅ©·Î°¡ ºÒ·¯Áö¸é ¾î¶² ÀÎÀڵ鵵 ¸ÅÅ©·Î È®ÀåÀÇ ¼öÇà ¾øÀÌ ´ëü µÈ´Ù. ¸ðµç `##' ¿¬»êÀÚ´Â Á¦°ÅµÇ°í ±×°ÍÀÇ ¾çÂÊ¿¡ ÅäÅ«µéÀº ÇϳªÀÇ ÅäÅ« ÇüÅ·Π¿¬°áµÈ´Ù.
Consider a C program that interprets named commands. There probably needs to be a table of commands, perhaps an array of structures declared as follows:
À̸§ Áö¾îÁø ¸í·ÉµéÀ» Çؼ®ÇÏ´Â C ÇÁ·Î±×·¥À» »ý°¢ÇغÁ¶ó. ¾Æ¸¶µµ ¸í·É Å×À̺íÀÌ ÇÊ¿äÇÒ °ÍÀÌ´Ù. ¾Æ¸¶µµ µÚµû¸£´Â ¼±¾ðµÈ ±¸Á¶Ã¼ÀÇ ¹è¿µµ ÀÏ °ÍÀÌ´Ù.
struct command { char *name; void (*function) (); }; struct command commands[] = { { "quit", quit_command}, { "help", help_command}, ... };
It would be cleaner not to have to give each command name twice, once in the string constant and once in the function name. A macro which takes the name of a command as an argument can make this unnecessary. The string constant can be created with stringification, and the function name by concatenating the argument with `_command'. Here is how it is done:
°¢ ¸í·É À̸§µéÀ» µÎ ¹ø ÁÖ´Â °ÍÀº ±ò²ûÇÏÁö ¾Ê´Ù. ÇѹøÀº ¹®ÀÚ¿ »ó¼ö¿Í ÇѹøÀº ÇÔ¼ö À̸§ÀÌ´Ù. ÀÎÀÚ·Î½á ¸í·ÉÀÇ À̸§À» ¹Þ¾ÆµéÀÌ´Â ¸ÅÅ©·Î´Â ÀÌ°ÍÀ» ºÒÇÊ¿äÇÏ°Ô ¸¸µé ¼ö ÀÖ´Ù. ¹®ÀÚ¿ »ó¼ö´Â stringification À¸·Î ¸¸µé¾îÁú ¼ö ÀÖ°í `_command' ¿Í ÇÔ²² ÀÎÀÚ¸¦ ¿¬°áÇؼ ÇÔ¼ö À̸§À¸·Î ¸¸µé ¼ö ÀÖ´Ù. ¾î¶»°Ô ÇÏ´ÂÁö ºÁ¶ó
#define COMMAND(NAME) { #NAME, NAME ## _command } struct command commands[] = { COMMAND (quit), COMMAND (help), ... };
The usual case of concatenation is concatenating two names (or a name and a number) into a longer name. This isn't the only valid case. It is also possible to concatenate two numbers (or a number and a name, such as `1.5' and `e3') into a number. Also, multi-character operators such as `+=' can be formed by concatenation. However, two tokens that don't together form a valid token cannot be concatenated. For example, concatenation of `x' on one side and `+' on the other is not meaningful because those two tokens do not form a valid preprocessing token when concatenated. UNDEFINED
¿¬°áÀÇ °æ¿ì Ç×»ó µÎ À̸§µéÀ»( ¶Ç´Â ÇϳªÀÇ À̸§°ú ÇϳªÀÇ ¼ýÀÚ) ´õ ±ä À̸§À¸·Î ¿¬°á ÇÑ´Ù. À̰͸¸ÀÌ Ç×»ó Á¤´çÇÑ °æ¿ì´Â ¾Æ´Ï´Ù. ¶ÇÇÑ µÎ°³ÀÇ ¼ýÀÚµé(¶Ç´Â ÇϳªÀÇ ¼ýÀÚ¿Í ÇϳªÀÇ À̸§, `1.5' ¿Í 'e3'¿Í °°Àº)À» ÇϳªÀÇ ¼ýÀÚ·Î ¿¬°á ÇÒ ¼ö ÀÖ´Ù. ¶ÇÇÑ `+='°ú °°Àº ´ÙÁß-¹®ÀÚ ¿¬»êÀÚ´Â ¿¬°á¿¡ ÀÇÇØ Çü½ÄÈ µÉ ¼ö ÀÖ´Ù. ±×·¯³ª ¿Ã¹Ù¸¥ ÅäÅ«À¸·Î Çü½ÄÈ µÇÁö ¾Ê´Â µÎ °³ÀÇ ÅäÅ«µéÀº ¿¬°á µÉ ¼ö ¾ø´Ù. ¿¹¸¦ µé¸é ÇÑ ÂÊÀº `x'°í ´Ù¸¥ ÂÊÀº `+'ÀÎ ¿¬°áÀº µÎ°³ÀÇ ÅäÅ«µéÀÌ ¿¬°á µÉ ¶§ Á¤´çÇÑ Àüó¸® ÅäÅ« ÇüÅ°¡ ¾Æ´Ï±â ¶§¹®¿¡ Àǹ̰¡ ¾ø´Ù. Á¤ÀÇ ¾È µÈ´Ù.
Keep in mind that the C preprocessor converts comments to whitespace before macros are even considered. Therefore, you cannot create a comment by concatenating `/' and `*': the `/*' sequence that starts a comment is not a token, but rather the beginning of a comment. You can freely use comments next to `##' in a macro definition, or in arguments that will be concatenated, because the comments will be converted to spaces at first sight, and concatenation operates on tokens and so ignores whitespace.
¸ÅÅ©·Î·Î »ý°¢Çϱâ Àü¿¡ ÁÖ¼®À» °ø¹éÀ¸·Î ÀüȯÇÏ´Â °ÍÀ» ¸í½ÉÇضó. ±×·¯¹Ç·Î ´ç½ÅÀº `/'°ú '*' ¿¬°á¿¡ ÀÇÇØ ÁÖ¼®À» ¸¸µé ¼ö ¾ø´Ù.: ÁÖ¼®À» ½ÃÀÛÇÏ´Â `/*' ¿Àº ÅäÅ«ÀÌ ¾Æ´Ï¶ó ÁÖ¼®ÀÇ ½ÃÀÛÀÌ´Ù. ´ç½ÅÀº ÀÚÀ¯·Ó°Ô ¸ÅÅ©·Î Á¤Àdzª ¶Ç´Â ¿¬°á µÇ¾îÁú ÀÎÀÚ¿¡¼ `##' ´ÙÀ½¿¡ ÁÖ¼®À» ÀÌ¿ëÇÒ ¼ö ÀÖ´Ù. ¿Ö³ÄÇϸé ÁÖ¼®µéÀº ù ´«¿¡ °ø°£À¸·Î Àüȯ µÉ °ÍÀÌ°í ÅäÅ«¿¡ ¿¬°áÀÌ ¼öÇàµÇ°í ±×·¡¼ °ø¹éÀº ¹«½Ã µÇ±â ¶§¹®ÀÌ´Ù.
To undefine a macro means to cancel its definition. This is done with the `#undef' directive. `#undef' is followed by the macro name to be undefined.
¸ÅÅ©·Î·Î Á¤ÀǸ¦ undefineÇÑ´Ù´Â °ÍÀº ±×°ÍÀÇ Á¤ÀǸ¦ Ãë¼ÒÇÏ´Â °ÍÀ» ÀǹÌÇÑ´Ù. `#undef' Áö½Ã¹®À¸·Î µÈ´Ù. `#undef' µÚ¿¡´Â Á¤ÀÇ°¡ Ãë¼ÒµÉ ¸ÅÅ©·Î À̸§ÀÌ µû¶ó ¿Â´Ù.
Like definition, undefinition occurs at a specific point in the source file, and it applies starting from that point. The name ceases to be a macro name, and from that point on it is treated by the preprocessor as if it had never been a macro name.
Á¤ÀÇ Ã³·³, Á¤ÀÇÀÇ Ãë¼Ò´Â ¼Ò½º ÆÄÀÏ¿¡ ƯÁ¤ ÁöÁ¡¿¡¼ ¹ß»ýÇÏ°í ±× ÁöÁ¡¿¡¼ Àû¿ëµÈ´Ù. ±× ÁöÁ¡¿¡¼ ¸ÅÅ©·Î À̸§Àº Ãë¼Ò µÇ°í °áÄÚ ¸ÅÅ©·Î À̸§ÀÌÁö ¾Ê¾Ò´ø °Íó·³ Àü󸮱⿡ ÀÇÇØ ´Ù·ç¾î Áø´Ù.
For example,
#define FOO 4 x = FOO; #undef FOO x = FOO;
expands into
x = 4; x = FOO;
In this example, `FOO' had better be a variable or function as well as (temporarily) a macro, in order for the result of the expansion to be valid C code.
ÀÌ ¿¹¿¡¼ `F00' ´Â È®ÀåÀÇ °á°ú°¡ ¿Ã¹Ù¸¥ C Äڵ尡 µÇ±â À§Çؼ (ÀÓ½ÃÀûÀ¸·Î) ¸ÅÅ©·Î¿Í ¸¶Âù°¡Áö·Î º¯¼ö³ª ÇÔ¼ö°¡ µÇ´Â °ÍÀÌ ´õ ³´´Ù.
The same form of `#undef' directive will cancel definitions with arguments or definitions that don't expect arguments. The `#undef' directive has no effect when used on a name not currently defined as a macro.
`#undef' Áö½Ã¹®°ú °°Àº Çü½ÄÀº ÀÎÀÚµéÀ̳ª ÀÎÀÚ¸¦ ÇÊ¿ä·Î ÇÏÁö ¾Ê´Â Á¤Àǵ鿡 Á¤ÀǸ¦ Ãë¼Ò ÇÒ °ÍÀÌ´Ù. `#undef' Áö½Ã¹®Àº ¸ÅÅ©·Î·Î½á ÇöÀç Á¤ÀÇ µÇÁö ¾ÊÀº À̸§À» »ç¿ëÇÒ ¶§ ÀüÇô È¿°ú°¡ ¾ø´Ù.
Redefining a macro means defining (with `#define') a name that is already defined as a macro.
RedefiningÀº ¸ÅÅ©·Î·Î½á ÀÌ¹Ì Á¤ÀÇµÈ À̸§À» (`#defind'À¸·Î) Á¤ÀÇ ÇÏ´Â °ÍÀ» ÀǹÌÇÑ´Ù.
A redefinition is trivial if the new definition is transparently identical to the old one. You probably wouldn't deliberately write a trivial redefinition, but they can happen automatically when a header file is included more than once (see section Header Files), so they are accepted silently and without effect.
ÀçÁ¤ÀÇ´Â »õ·Î¿î Á¤ÀÇ°¡ ¸í¹éÇÏ°Ô Àü¿¡ Á¤ÀÇ¿Í °°´Ù¸é »ç¼ÒÇÑ °ÍÀÌ´Ù. ¾Æ¸¶µµ ´ç½ÅÀº ½ÅÁßÇÏ°Ô ÇÏÂúÀº ÀçÁ¤ÀǸ¦ ¾²´Â °ÍÀÌ ¾Æ´Ï°í ±×°ÍµéÀº Çì´õ ÆÄÀÏÀÌ Çѹø ´õ ¼Ò½º¿¡ Æ÷Ç﵃ ¶§ ÀÚµ¿ÀûÀ¸·Î ¹ß»ýÇÑ´Ù. ±×·¡¼ ±×°ÍµéÀº ¼Ò¸® ¾øÀÌ ¹Þ¾Æ µé¿©Áö°í È¿°úµµ ¾ø´Ù.
Nontrivial redefinition is considered likely to be an error, so it provokes a warning message from the preprocessor. However, sometimes it is useful to change the definition of a macro in mid-compilation. You can inhibit the warning by undefining the macro with `#undef' before the second definition.
»ç¼ÒÇÏÁö ¾ÊÀº ÀçÁ¤ÀÇ´Â ¿¡·¯ °°ÀÌ »ý°¢ µÉÁö ¸ð¸¥´Ù. ±×·¡¼ Àü󸮱â·ÎºÎÅÍ °æ°í¸¦ ¾ß±â ½ÃŲ´Ù. ±×·¯³ª °¡²û Áß°£ ÄÄÆÄÀÏ¿¡¼ ¸ÅÅ©·Î Á¤ÀǸ¦ ¹Ù²Ü ¶§ À¯¿ëÇÏ´Ù. ´ç½ÅÀº µÎ ¹ø° Á¤ÀÇ Àü¿¡ `#undef'·Î Á¤ÀǸ¦ Ãë¼ÒÇؼ °æ°í¸¦ ±ÝÁö ÇÒ ¼ö ÀÖ´Ù.
In order for a redefinition to be trivial, the parameter names must match and be in the same order, and the new replacement list must exactly match the one already in effect, with two possible exceptions:
»ç¼ÒÇÑ ÀçÁ¤ÀǸ¦ À§Çؼ, ÆĶó¹ÌÅÍ À̸§µéÀº ÀÏÄ¡ÇØ¾ß ÇÏ°í °°Àº ¼ø¼°¡ µÇ¾î¾ß¸¸ ÇÑ´Ù. ±×¸®°í »õ·Î¿î ±³Ã¼ ¸ñ·ÏÀº Á¤È®ÇÏ°Ô È¿°ú°¡ ÀÏÄ¡Çؾ߸¸ ÇÑ´Ù. µÎ °¡Áö °¡´ÉÇÑ ¿¹¿Ü°¡ ÀÖ´Ù.
Recall that a comment counts as whitespace.
°ø¹éÀ¸·Î½á ÁÖ¼®À» ¿©±â´Â °ÍÀ» ´Ù½Ã »ó±â½ÃÄѶó.
As a particular case of the above, you may not redefine an object-like macro as a function-like macro, and vice-versa.
À§ÀÇ Æ¯º°ÇÑ ¿¹·Î½á ´ç½ÅÀºfunction-like ¸ÅÅ©·Î °°ÀÌ object-like ¸ÅÅ©·Î¸¦ ÀçÁ¤ÀÇ ÇÏÁö ¾ÊÀ» °ÍÀÌ´Ù. ¹Ý´ëÀÇ °æ¿ìµµ ¸¶Âù°¡Áö´Ù.
Sometimes, there is an identifier that you want to remove completely from your program, and make sure that it never creeps back in. To enforce this, the `#pragma GCC poison' directive can be used. `#pragma GCC poison' is followed by a list of identifiers to poison, and takes effect for the rest of the source. You cannot `#undef' a poisoned identifier or test to see if it's defined with `#ifdef'.
¶§¶§·Î ´ç½ÅÀÌ ¿øÇÏ´Â °ÍÀ» ´ç½ÅÀÇ ÇÁ·Î±×·¥¿¡¼ ¿Ïº®ÇÏ°Ô Á¦°ÅÇÏ´Â °ÍÀ» ¿øÇÏ´Â ½Äº°ÀÚ°¡ ÀÖ´Ù. ±×¸®°í °áÄÚ ±×°ÍÀº ´Ù½Ã ½½Â½( ^^;) µé¾î¿ÀÁö ¾Ê´Â °ÍÀ» È®½Å ÇÒ ¼ö Àֱ⸦ ¿øÇÒ °ÍÀÌ´Ù. ÀÌ°ÍÀ» °Á¦ÀûÀ¸·Î Á¦ÇÑ Çϱâ À§Çؼ `#pragma GCC poison' Áö½Ã¹®ÀÌ »ç¿ë µÉ ¼ö ÀÖ´Ù. `#prgma GCC poison' µÚ¿¡´Â poison¿¡ ½Äº°ÀÚµéÀÇ ¸ñ·ÏÀÌ ³ª¿Â´Ù. ±×¸®°í ¼Ò½ºÀÇ ³ª¸ÓÁö¸¦ À§ÇÑ ³ë·ÂÀÌ ¿Â´Ù( ^^~). ´ç½ÅÀº ¸ø¾²°Ô µÈ ½Äº°ÀÚµéÀ» `#undef' ÇÒ ¼ö ¾ø°í, ¶ÇÇÑ `#ifdef'·Î Á¤ÀÇ ÇÏ¸é º¸ÀÌ´ÂÁö Å×½ºÆ® ÇÒ ¼ö ¾ø´Ù.
For example,
¿¹¸¦ µé¸é
#pragma GCC poison printf sprintf fprintf sprintf(some_string, "hello");
will produce an error.
¿¡·¯°¡ ¹ß»ý ÇÑ´Ù.
In this section we describe some special rules that apply to macros and macro expansion, and point out certain cases in which the rules have counterintuitive consequences that you must watch out for.
ÀÌ ¼½¼Ç¿¡¼ ¿ì¸®´Â ¸ÅÅ©·Î¸¦ Àû¿ë°ú È®Àå¿¡ ´ëÇÑ ¸î °³ÀÇ Æ¯º°ÇÑ ±ÔÄ¢µéÀ» ¼³¸íÇÑ´Ù. ±×¸®°í ´ç½ÅÀÌ ºÁ¾ß¸¸ ÇÏ´Â counterintuitive consequences¸¦ °®´Â ±ÔÄ¢¿¡ È®½ÇÇÑ °æ¿ì¸¦ ÁöÀûÇÑ´Ù.
Recall that when a macro is called with arguments, the arguments are substituted into the macro body and the result is checked, together with the rest of the input file, for more macro calls.
ÀÎÀÚµé°ú ÇÔ²² ¸ÅÅ©·Î°¡ È£Ãâ µÉ ¶§ ÀÎÀÚµéÀº ¸ÅÅ©·Î ¸öü·Î ´ëü µÇ°í °á°ú´Â ÀÔ·Â ÆÄÀϵéÀÇ ³ª¸ÓÁö¿Í ÇÔ²² ´õ ¸¹Àº ¸ÅÅ©·Î È£ÃâÀ» À§ÇØ Ã¼Å©µÈ´Ù.
It is possible to piece together a macro call coming partially from the macro body and partially from the arguments. For example,
¸ÅÅ©·Î ¸öü¿Í ÀÎÀÚµé·ÎºÎÅÍ ºÎºÐÀûÀ¸·Î ¿À´Â ¸ÅÅ©·Î È£ÃâÀ» ÇÔ²² ´ÜÆíÈ ÇÏ´Â °ÍÀÌ °¡´ÉÇÏ´Ù. ¿¹¸¦ µé¸é,
#define double(x) (2*(x)) #define call_with_1(x) x(1)
would expand `call_with_1 (double)' into `(2*(1))'.
Macro definitions do not have to have balanced parentheses. By writing an unbalanced open parenthesis in a macro body, it is possible to create a macro call that begins inside the macro body but ends outside of it. For example,
¸ÅÅ©·Î Á¤ÀǵéÀº ±ÕÇü ¸ÂÀº °ýÈ£µéÀ» °®Áö ¾Ê¾Æ¾ß¸¸ ÇÑ´Ù. ±ÕÇüÀÌ ¸ÂÁö ¾Ê´Â ¸ÅÅ©·Î ¸öü¿¡ ¿±â °ýÈ£´Â ¸ÅÅ©·Î ¸öü ¾È¿¡¼ (³¡¿¡ ¹Ù±ùÂÊÀº Á¦¿ÜÇÏ°í) ½ÃÀÛÇÏ´Â ¸ÅÅ©·Î¸¦ ¸¸µé ¼ö ÀÖ´Ù. ¿¹¸¦ µé¸é,
#define strange(file) fprintf (file, "%s %d", ... strange(stderr) p, 35)
This bizarre example expands to `fprintf (stderr, "%s %d", p, 35)'!
ÀÌ ²ûÂïÇÑ ¿¹´Â `fprintf (stderr, "%s %d", p, 35)'·Î È®Àå µÈ´Ù. ¤Ñ¤Ñ;
You may have noticed that in most of the macro definition examples shown above, each occurrence of a macro argument name had parentheses around it. In addition, another pair of parentheses usually surround the entire macro definition. Here is why it is best to write macros that way.
´ç½ÅÀº ´ëºÎºÐÀÇ À§¿¡¼ º¸¿©ÁØ ¸ÅÅ©·Î Á¤ÀÇ ¿¹¿¡¼ ¸ÅÅ©·Î ÀÎÀÚµéÀÌ ¹ß»ýÇÏ¸é ±×°ÍÀÇ ÁÖÀ§¿¡ °ýÈ£°¡ ÀÖ´ø °ÍÀ» ¾Ë¾Æ ë´ÂÁö ¸ð¸£°Ú´Ù. µ¡ºÙÀÌÀÚ¸é ´Ù¸¥ °ýÈ£ÀÇ ½ÖµéÀÌ Ç×»ó Àüü ¸ÅÅ©·Î Á¤ÀǸ¦ °¨»ç°í ÀÖ´Ù. ¿©±â¼ ¿Ö ±× ¹æ¹ýÀÌ ¸ÅÅ©·ÎµéÀ» ¾²´Â ÃÖ°íÀÇ ¹æ¹ýÀÎÁö¸¦ ¾²°Ú´Ù.
Suppose you define a macro as follows,
´ÙÀ½°ú °°Àº Á¤ÀǸ¦ °¡Á¤ÇØ º¸ÀÚ.
#define ceil_div(x, y) (x + y - 1) / y
whose purpose is to divide, rounding up. (One use for this operation is to compute how many `int' objects are needed to hold a certain number of `char' objects.) Then suppose it is used as follows:
³ª´©°í ¿Ã¸²Çϱâ À§ÇÑ °ÍÀÌ´Ù.( ÇÑ »ç¿ë¹ýÀº ¾ó¸¶³ª ¸¹Àº `int' °´Ã¼°¡ `char' °´Ã¼µéÀÇ È®½ÇÇÑ ¼ýÀÚ¸¦ °íÁ¤Çϱâ À§ÇØ ÇÊ¿äÇÑÁö¸¦ °è»êÇϱâ À§ÇÑ °ÍÀÌ´Ù. ±× ´ÙÀ½¿¡ ±×°ÍÀÌ ´ÙÀ½°ú °°ÀÌ ¾²ÀÎ´Ù°í °¡Á¤ÇÏÀÚ.
a = ceil_div (b & c, sizeof (int));
This expands into
ÀÌ°ÍÀº ´ÙÀ½À¸·Î È®Àå µÈ´Ù.
a = (b & c + sizeof (int) - 1) / sizeof (int);
which does not do what is intended. The operator-precedence rules of C make it equivalent to this:
Àǵµ µÈ °ÍÀº ÇÏÁö ¾Ê´Â´Ù. operator-precedence CÀÇ ±ÔÄ¢µéÀº ÀÌ°ÍÀ» µ¿µîÇÏ°Ô ¸¸µç´Ù.
a = (b & (c + sizeof (int) - 1)) / sizeof (int);
What we want is this:
ÀÌ°ÍÀÌ ¿ì¸®°¡ ¿øÇÏ´Â °ÍÀÌ´Ù.
a = ((b & c) + sizeof (int) - 1)) / sizeof (int);
Defining the macro as
#define ceil_div(x, y) ((x) + (y) - 1) / (y)
provides the desired result.
Unintended grouping can result in another way. Consider `sizeof ceil_div(1, 2)'. That has the appearance of a C expression that would compute the size of the type of `ceil_div (1, 2)', but in fact it means something very different. Here is what it expands to:
Àǵµ ÇÏÁö ¾ÊÀº ±×·ìÈ´Â ´Ù¸¥ °á°ú¸¦ ³ºÀ» ¼ö ÀÖ´Ù. `sizeof ceil_div(1, 2)'¸¦ °í·ÁÇغÁ¶ó. ±×°ÍÀº `ceil_div (1, 2)' ŸÀÔÀÇ »çÀÌÁ °è»êÇÏ´Â C Ç¥ÇöÀÇ ¿ÜÇüÀ» °®´Â´Ù. ÇÏÁö¸¸ »ç½Ç ±×°ÍÀº ¸Å¿ì ´Ù¸¥ Àǹ̸¦ °®´À´Ù. ¿©±â È®ÀåµÈ °ÍÀÌ ÀÖ´Ù
sizeof ((1) + (2) - 1) / (2)
This would take the size of an integer and divide it by two. The precedence rules have put the division outside the `sizeof' when it was intended to be inside.
ÀÌ°ÍÀº Á¤¼ö Å©±â¸¦ ¹Þ°í 2·Î ±×°ÍÀ» ³ª´«´Ù. ¼±ÇàµÈ ±ÔÄ¢µéÀº ³ª´©´Â ¼ö¸¦ `sizeof' ¹Ù±ù¿¡ ³ù´Ù. ±×°ÍÀÌ ¾È¿¡ ³õ¿©Áö°Ô ÀǵµµÇ¾î¾ß ÇÒ ¶§ ¸»ÀÌ´Ù.
Parentheses around the entire macro definition can prevent such problems. Here, then, is the recommended way to define `ceil_div':
Àüü ¸ÅÅ©·Î Á¤ÀÇ¿¡ °ýÈ£´Â ±×·± ¹®Á¦µéÀ» ¸·À» ¼ö ÀÖ´Ù. `ceil_div'¸¦ Á¤ÀÇ ÇÏ´Â ¹æ¹ýÀ¸·Î ÃßõµÇ´Â ¹æ¹ýÀÌ ÀÖ´Ù.:
#define ceil_div(x, y) (((x) + (y) - 1) / (y))
Often it is desirable to define a macro that expands into a compound statement. Consider, for example, the following macro, that advances a pointer (the argument `p' says where to find it) across whitespace characters:
º¹ÀâÇÑ ¹®ÀåÀ¸·Î È®ÀåµÇ´Â ¸ÅÅ©·Î¸¦ Á¤ÀÇ ÇÏ´Â °ÍÀº ¸Å·ÂÀûÀÌ´Ù. ¿¹¸¦ µé¾î, °ø¹é ¹®ÀÚµé·Î °¡·ÎÁö¸£´Â Æ÷ÀÎÅ͸¦ °³¼± ½ÃÅ°´Â °ÍÀ» »ý°¢ÇØ ºÁ¶ó.
#define SKIP_SPACES(p, limit) \ { register char *lim = (limit); \ while (p != lim) { \ if (*p++ != ' ') { \ p--; break; }}}
Here backslash-newline is used to split the macro definition, which must be a single logical line, so that it resembles the way such C code would be laid out if not part of a macro definition.
backslash-newlineÀº ÇÑ ³í¸® ¶óÀÎÀÌ µÇ¾ß¸¸ ÇÏ´Â ¸ÅÅ©·Î Á¤ÀǸ¦ ³ª´©´Âµ¥ »ç¿ëµÈ´Ù. ±×·¡¼ ¸ÅÅ©·Î Á¤ÀÇ ºÎºÐÀÌ ¾Æ´Ï¶ó¸é C Äڵ忡¼ ¾²´Â ¹æ¹ýÀ» ´à¾Ò´Ù
A call to this macro might be `SKIP_SPACES (p, lim)'. Strictly speaking, the call expands to a compound statement, which is a complete statement with no need for a semicolon to end it. However, since it looks like a function call, it minimizes confusion if you can use it like a function call, writing a semicolon afterward, as in `SKIP_SPACES (p, lim);'
ÀÌ ¸ÅÅ©·Î È£ÃâÀº `SKIP_SPACES (p, lim)'°¡ µÉ °ÍÀÌ´Ù. ¾ö¹ÐÇÏ°Ô ¸»Çؼ º¹ÀâÇÑ ¹®ÀåÀ¸·Î È®ÀåµÈ È£Ãâ¿¡¼ ±×°ÍÀÇ ¿ÏÀüÇÑ ¹®ÀåÀº ³¡¿¡ ¼¼¹ÌÄÝ·ÐÀÌ ÇÊ¿äÇÏÁö ¾Ê´Ù. ±×·¯³ª ÇÔ¼ö È£Ãâ ó·³ º¸À̱⠶§¹®¿¡ ´ç½ÅÀÌ µÚÂÊ¿¡ `SKIP_SPACES (p, lim);'ó·³ ¼¼¹ÌÄÝ·ÐÀ» ¾²¸é ÇÔ¼ö °°ÀÌ »ç¿ëÇصµ È¥¶õÀ» ÃÖ¼ÒÈ ÇÒ ¼ö ÀÖ´Ù.
This can cause trouble before `else' statements, because the semicolon is actually a null statement. Suppose you write
ÀÌ°ÍÀº `else' ¹®Àå Àü¿¡ ¹®Á¦¸¦ ¾ß±â ½Ãų ¼ö ÀÖ´Ù. ¿Ö³ÄÇÏ¸é ¼¼¹ÌÄÝ·ÐÀº ½ÇÁ¦·Î null ¹®ÀåÀÌ´Ù.
if (*p != 0) SKIP_SPACES (p, lim); else ...
The presence of two statements -- the compound statement and a null statement -- in between the `if' condition and the `else' makes invalid C code.
`if' Á¶°Ç°ú `else' »çÀÌ¿¡ µÎ ¹®Àå- º¹ÀâÇÑ ¹®Àå°ú null ¹®Àå-- ÀÇ Á¸Àç´Â ¿Ã¹Ù¸£Áö ¾ÊÀº C Äڵ带 ¸¸µç´Ù.
The definition of the macro `SKIP_SPACES' can be altered to solve this problem, using a `do ... while' statement. Here is how:
¸ÅÅ©·Î `SKIP_SPACES'´Â ÀÌ ¹®Á¦¸¦ ÇØ°áÇϱâ À§ÇØ `do ... while'¹®ÀåÀ» »ç¿ëÇؼ ¹Ù²ð ¼ö ÀÖ´Ù.
#define SKIP_SPACES(p, limit) \ do { register char *lim = (limit); \ while (p != lim) { \ if (*p++ != ' ') { \ p--; break; }}} \ while (0)
Now `SKIP_SPACES (p, lim);' expands into
do {...} while (0);
which is one statement.
Many C programs define a macro `min', for "minimum", like this:
¸¹Àº C ÇÁ·Î±×·¥µéÀº "ÃÖ¼Ò"¿¡ ´ëÇØ `min'¸¦ Á¤ÀÇ ÇÑ´Ù. ÀÌ°Í°ú °°´Ù.
#define min(X, Y) ((X) < (Y) ? (X) : (Y))
When you use this macro with an argument containing a side effect, as shown here,
´ç½ÅÀÌ ºÎ°¡Àû È¿°ú¸¦ Æ÷ÇÔÇÏ´Â ÀÎÀÚ¸¦ ÀÌ ¸ÅÅ©·Î¿¡ »ç¿ëÇÒ ¶§´Â ¾Æ·¡¿Í °°´Ù.
next = min (x + y, foo (z));
it expands as follows:
´ÙÀ½ ó·³ È®Àå µÈ´Ù
next = ((x + y) < (foo (z)) ? (x + y) : (foo (z)));
where `x + y' has been substituted for `X' and `foo (z)' for `Y'.
`x + y'´Â `X'·Î ´ëü µÇ°í ¿Í `foo(z)'´Â Y·Î ´ëü µÈ´Ù.
The function `foo' is used only once in the statement as it appears in the program, but the expression `foo (z)' has been substituted twice into the macro expansion. As a result, `foo' might be called two times when the statement is executed. If it has side effects or if it takes a long time to compute, the results might not be what you intended. We say that `min' is an unsafe macro.
`foo' ÇÔ¼ö´Â ÇÁ·Î±×·¥¿¡ ³ªÅ¸³ª´Â °Åó·³ ¹®Àå¿¡ ¿ÀÁ÷ Çѹø »ç¿ëµÈ´Ù. ±×·¯³ª `foo(z)' Ç¥ÇöÀº ¸ÅÅ©·Î È®ÀåÀ¸·Î µÎ ¹ø ´ëü µÇ¾îÁø´Ù. °á°ú·Î½á, `foo'´Â ¹®ÀåÀÌ ½ÇÇàµÉ ¶§ µÎ ¹ø ºÒ·ÁÁúÁö ¸ð¸¥´Ù. ºÎ°¡Àû È¿°ú¸¦ °®°Å³ª ¶Ç´Â °è»êÇϴµ¥ ¿À·£ ½Ã°£ÀÌ ¼Ò¸ð µÈ´Ù¸é °á°ú´Â ´ç½ÅÀÌ ÀǵµÇÑ °ÍÀÌ ¾Æ´ÒÁöµµ ¸ð¸¥´Ù. ¿ì¸®´Â `min'Àº ¾ÈÀüÇÏÁö ¾ÊÀº ¸ÅÅ©·Î¶ó°í ¸»ÇÑ´Ù.
The best solution to this problem is to define `min' in a way that computes the value of `foo (z)' only once. The C language offers no standard way to do this, but it can be done with GNU C extensions as follows:
ÀÌ ¹®Á¦¸¦ ÇØ°áÇÏ´Â ÃÖ°íÀÇ ¹æ¹ýÀº `min'À» ¿ÀÁ÷ Çѹø `foo (z)' °ªÀ¸·Î °è»êÇÏ´Â °ÍÀÌ´Ù. C ¾ð¾î´Â ÀÌ°ÍÀ» Çϴ ǥÁØ ¹æ¹ýÀ» Á¦°øÇÏÁö ¾ÊÁö¸¸ GNU C È®ÀåÀ¸·Î ´ÙÀ½Ã³·³ ÇÒ ¼ö ÀÖ´Ù.
#define min(X, Y) \ ({ typeof (X) __x = (X), __y = (Y); \ (__x < __y) ? __x : __y; })
If you do not wish to use GNU C extensions, the only solution is to be careful when using the macro `min'. For example, you can calculate the value of `foo (z)', save it in a variable, and use that variable in `min':
¸¸¾à¿¡ ´ç½ÅÀÌ GNU C È®ÀåµéÀ» »ç¿ëÇÏ´Â °ÍÀ» ¿øÇÏÁö ¾Ê´Â ´Ù¸é ¸ÅÅ©·Î `min'À» Á¶½É½º·´°Ô »ç¿ëÇÏ´Â ¹æ¹ý ¹Û¿¡ ¾ø´Ù. ¿¹¸¦ µé¸é ´ç½ÅÀº `foo(z)¸¦ º¯¼ö¿¡ ÀúÀåÇÏ°í `min'¿¡ ±× º¯¼ö¸¦ »ç¿ëÇؼ `foo(z)' °ªÀ» °è»ê ÇÒ ¼ö ÀÖ´Ù.
#define min(X, Y) ((X) < (Y) ? (X) : (Y)) ... { int tem = foo (z); next = min (x + y, tem); }
(where we assume that `foo' returns type `int').
A self-referential macro is one whose name appears in its definition. A special feature of ISO Standard C is that the self-reference is not considered a macro call. It is passed into the preprocessor output unchanged.
ÀÚ±â ÂüÁ¶ ¸ÅÅ©·Î´Â ±×°ÍÀÇ Á¤ÀÇ¿¡ À̸§ÀÌ ³ªÅ¸³ª´Â °ÍÀÌ´Ù. ISO Ç¥ÁØ CÀÇ Æ¯º°ÇÑ Æ¯Â¡Àº ÀÚ±â ÂüÁ¶´Â ¸ÅÅ©·Î È£Ãâ·Î °í·ÁµÇÁö ¾Ê´Â °ÍÀÌ´Ù. ±×°ÍÀº ¹Ù²îÁö ¾ÊÀº Àüó¸® Ãâ·ÂÀ¸·Î Åë°úµÈ´Ù.
Let's consider an example:
¿¹¸¦ »ý°¢ÇØ º¸ÀÚ
#define foo (4 + foo)
where `foo' is also a variable in your program.
`foo'´Â ¶ÇÇÑ ´ç½Å ÇÁ·Î±×·¥ÀÇ º¯¼öÀÌ´Ù.
Following the ordinary rules, each reference to `foo' will expand into `(4 + foo)'; then this will be rescanned and will expand into `(4 + (4 + foo))'; and so on until it causes a fatal error (memory full) in the preprocessor.
º¸ÅëÀÇ ±ÔÄ¢µé¿¡ µû¶ó °¢°¢ÀÇ `foo'¿¡¼ ÂüÁ¶´Â `(4 + foo)'·Î È®ÀåµÉ °ÍÀÌ´Ù; ±× ´ÙÀ½¿¡ ÀÌ°ÍÀº ´Ù½Ã °Ë»öµÇ°í `(4 + (4 + foo))' ·Î È®ÀåµÉ °ÍÀÌ´Ù; ±×¸®°í ±×°ÍÀÌ ¸Þ¸ð¸®°¡ ´Ù Â÷´Â Ä¡¸íÀûÀÎ Àü󸮱⠿¡·¯¸¦ ¾ß±â ½Ãų ¶§ ±îÁö °è¼Ó µÉ °ÍÀÌ´Ù.
However, the special rule about self-reference cuts this process short after one step, at `(4 + foo)'. Therefore, this macro definition has the possibly useful effect of causing the program to add 4 to the value of `foo' wherever `foo' is referred to.
±×·¯³ª. ÀÚ±â ÂüÁ¶¿¡ ´ëÇÑ Æ¯º°ÇÑ ±ÔÄ¢Àº Çѹø¿¡ ½ºÅÜ µÚ¿¡¼ ÀÌ ÇÁ·Î¼¼½º´Â ª°Ô ²÷´Â´Ù. ±×·¯¹Ç·Î ÀÌ ¸ÅÅ©·Î Á¤ÀÇ´Â `foo`°¡ ÂüÁ¶µÇ´Â ¾î´À °÷¿¡¼µçÁö `foo'ÀÇ °ª¿¡ 4¸¦ ´õÇÏ´Â ÇÁ·Î±×·¥ È¿°ú¸¦ ¾ò±â¿¡ À¯¿ëÇÒ ¼ö ÀÖ´Ù.
In most cases, it is a bad idea to take advantage of this feature. A person reading the program who sees that `foo' is a variable will not expect that it is a macro as well. The reader will come across the identifier `foo' in the program and think its value should be that of the variable `foo', whereas in fact the value is four greater.
´ëºÎºÐÀÇ °æ¿ì, ÀÌ Æ¯Â¡ÀÇ ÀÌÁ¡À» ¹Þ¾ÆµéÀÌ´Â °ÍÀÌ ÁÁÁö ¾ÊÀº »ý°¢ÀÌ´Ù. `foo` º¯¼ö¸¦ ´ç½Å ÇÁ·Î±×·¥¿¡¼ Àд »ç¶÷Àº ÀÌ ¸ÅÅ©·Î¿¡ ´ëÇØ ÀüÇô ¿¹»ó ÇÏÁö ¸ø ÇÒ °ÍÀÌ´Ù. Àд »ç¶÷Àº ÇÁ·Î±×·¥¿¡¼ `foo' ½Äº°ÀÚ¸¦ °Ç³Ê ¶ç°í ±×°ÍÀÇ °ªÀº `foo' º¯¼ö°¡ µÇ¾ß ÇÑ´Ù°í »ý°¢ÇÒ °ÍÀÌ´Ù. ¹Ý¸é¿¡ »ç½Ç °ªÀº 4°¡ ´õ Å« °ÍÀε¥..
The special rule for self-reference applies also to indirect self-reference. This is the case where a macro x expands to use a macro `y', and the expansion of `y' refers to the macro `x'. The resulting reference to `x' comes indirectly from the expansion of `x', so it is a self-reference and is not further expanded. Thus, after
ÀÚ±â ÂüÁ¶¿¡ ´ëÇÑ Æ¯º°ÇÑ ±ÔÄ¢Àº ¶ÇÇÑ ÀÚ±âÂüÁ¶¸¦ °£Á¢ÀûÀ¸·Î Àû¿ëÇÑ´Ù. ÀÌ°ÍÀº ¸ÅÅ©·Î x°¡ ¸ÅÅ©·Î `y'¸¦ »ç¿ëÇؼ È®ÀåµÇ´Â °æ¿ìÀÌ´Ù. ±×¸®°í `y'ÀÇ È®ÀåÀº ¸ÅÅ©·Î `x'¸¦ ÂüÁ¶ µÈ´Ù. `x' ÂüÁ¶ÀÇ °á°ú´Â °£Á¢ÀûÀ¸·Î `x'ÀÇ È®ÀåÀ¸·ÎºÎÅÍ ¿Â´Ù. ±×·¡¼ ±×°ÍÀº ÀÚ±â ÂüÁ¶ÀÌ°í ´õ È®ÀåµÇÁö ¾Ê´Â´Ù.
#define x (4 + y) #define y (2 * x)
`x' would expand into `(4 + (2 * x))'. Clear?
Suppose `y' is used elsewhere, not from the definition of `x'. Then the use of `x' in the expansion of `y' is not a self-reference because `x' is not "in progress". So it does expand. However, the expansion of `x' contains a reference to `y', and that is an indirect self-reference now because `y' is "in progress". The result is that `y' expands to `(2 * (4 + y))'.
`y'°¡ ¾²ÀÌ´Â 'x'ÀÇ Á¤ÀǷκÎÅÍ Á¤ÀÇ µÇÁö ¾Ê´Â ´Ù¸¥ °÷À» °¡Á¤ÇÏÀÚ. ±× ´ÙÀ½¿¡ `x'¸¦ `y'ÀÇ È®Àå¿¡ »ç¿ëÇÏ´Â °ÍÀº ÀÚ±â ÂüÁ¶°¡ ¾Æ´Ï´Ù. ¿Ö³ÄÇϸé `x'´Â "in progress"°¡ ¾Æ´Ï±â ¶§¹®ÀÌ´Ù. ±×·¡¼ ±×°ÍÀº È®ÀåµÈ´Ù. ±×·¯³ª `x'È®ÀåÀº `y' ÂüÁ¶¸¦ Æ÷ÇÔÇÑ´Ù. ±×¸®°í ±×°ÍÀº `y'°¡ "in progress" À̱⠶§¹®¿¡ °£Á¢ÀûÀÎ ÀÚ±â ÂüÁ¶ÀÌ´Ù. °á°ú´Â 'y'´Â `(2 * (4 + y))'·Î È®Àå µÈ´Ù.
This behavior is specified by the ISO C standard, so you may need to understand it.
ÀÌ ÇൿµéÀº ISO CÇ¥ÁØ¿¡ ÀÇÇØ ±¸Ã¼È µÇ¾ú´Ù. ±×·¡¼ ´ç½ÅÀº ±×°ÍÀ» ÀÌÇØÇÏ´Â °ÍÀÌ ÇÊ¿äÇÒ °ÍÀÌ´Ù.
We have explained that the expansion of a macro, including the substituted arguments, is re-scanned for macro calls to be expanded.
¿ì¸®´Â ´ëüµÇ´Â ÀÎÀÚµéÀ» Æ÷ÇÔÇؼ ¸ÅÅ©·Î È®ÀåÀ» ¸ÅÅ©·Î È£ÃâÀÌ È®ÀåµÇ´Â °ÍÀ¸·Î ´Ù½Ã °Ë»öÇÏ´Â °ÍÀ» ¼³¸íÇØ ¿Ô´Ù
What really happens is more subtle: first each argument is scanned separately for macro calls. Then the resulting tokens are substituted into the macro body to produce the macro expansion, and the macro expansion is scanned again for macros to expand.
Á¤¸»·Î ÀÏ¾î³ °ÍÀº ´õ ±¸º°Çϱ⠾î·Æ´Ù: óÀ½ °¢°¢ÀÇ ÀÎÀÚ´Â ¸ÅÅ©·Î È£ÃâµéÀ» À§ÇØ ºÐ¸® µÇ¼ °Ë»öµÈ´Ù. ±× ´ÙÀ½¿¡ °á°ú ÅäÅ«Àº ¸ÅÅ©·Î È®ÀåÀ» ¸¸µå´Â ¸ÅÅ©·Î ¸öü·Î ´ëüµÈ´Ù. ±×¸®°í ¸ÅÅ©·Î È®ÀåÀº ´Ù½Ã ¸ÅÅ©·Î°¡ È®ÀåµÇ´Â °ÍÀ» °Ë»öÇÑ´Ù.
The result is that the arguments are scanned twice to expand macro calls in them.
°á°ú´Â ÀÎÀÚµéÀÌ È®ÀåµÇ´Â ¸ÅÅ©·Î È£Ãâ¿¡¼ µÎ ¹ø ½ºÄµµÈ´Ù.
Most of the time, this has no effect. If the argument contained any macro calls, they are expanded during the first scan. The result therefore contains no macro calls, so the second scan does not change it. If the argument were substituted as given, with no prescan, the single remaining scan would find the same macro calls and produce the same results.
´ëü·Î ÀÌ°ÍÀº È¿°ú°¡ ¾ø´Ù. ¸¸¾à ¾î¶² ¸ÅÅ©·Î È£Ãâ¿¡ Æ÷ÇÔµÈ ÀÎÀÚµéÀ̶ó¸é ±×°ÍµéÀº óÀ½ °Ë»öµ¿¾È È®Àå µÉ °ÍÀÌ´Ù. ±×·¯¹Ç·Î °á°ú´Â ¾Æ¹« ¸ÅÅ©·Î È£Ãâµµ Æ÷ÇÔÇÏÁö ¾Ê´Â´Ù. ±×·¡¼ µÎ ¹ø° °Ë»ö¿¡¼´Â ±×°ÍÀÌ ¹Ù²îÁö ¾Ê´Â´Ù. ¸¸¾à ¼±Çà °Ë»ö ¾øÀÌ ÀÎÀÚ°¡ ÁÖ¾îÁø °Íó·³ ´ëü µÇ¸é, Çϳª ³²Àº °Ë»öÀº °°Àº ¸ÅÅ©·Î È£ÃâµéÀ» ãÀ» °ÍÀÌ°í °°Àº °á°ú¸¦ ¸¸µé °ÍÀÌ´Ù.
You might expect the double scan to change the results when a self-referential macro is used in an argument of another macro (see section Self-Referential Macros): the self-referential macro would be expanded once in the first scan, and a second time in the second scan. However, this is not what happens. The self-references that do not expand in the first scan are marked so that they will not expand in the second scan either.
ÀÚ±â ÂüÁ¶ ¸ÅÅ©·Î°¡ ´Ù¸¥ ¸ÅÅ©·ÎÀÇ ÀÎÀÚ¸¦ »ç¿ëÇÒ ¶§ ´ç½ÅÀº ¹Ù²ï °á°ú¿¡ µÎ ¹ø °Ë»öÀ» ¿¹»óÇÒ Áö ¸ð¸¥´Ù: ÀÚ±âÂüÁ¶ ¸ÅÅ©·Î´Â ù °Ë»ö¿¡¼ Çѹø È®ÀåµÈ´Ù. ±×¸®°í ´ÙÀ½ °Ë»ö¿¡¼ µÎ ¹ø°·Î È®ÀåµÉ °ÍÀÌ´Ù. ±×·¯³ª ÀÌ°ÍÀº ÀϾÁö ¾Ê´Â´Ù. ù °Ë»ö¿¡¼ È®ÀåÇÏÁö ¾Ê´Â ÀÚ±â ÂüÁ¶´Â µÎ ¹ø° °Ë»ö¿¡¼µµ ¶ÇÇÑ È®ÀåÇÏÁö ¾Ê±â À§ÇØ Ç¥½Ã µÉ °ÍÀÌ´Ù..
The prescan is not done when an argument is stringified or concatenated. Thus,
¼±Çà °Ë»öÀº ÀÎÀÚ°¡ ¹®ÀÚ¿È ¶Ç´Â ¿¬°áµÇÁö ¾ÊÀ» ¶§ ³¡³ªÁö ¾Ê´Â´Ù. °Ô´Ù°¡
#define str(s) #s #define foo 4 str (foo)
expands to `"foo"'. Once more, prescan has been prevented from having any noticeable effect.
`"foo"'·Î È®Àå µÈ´Ù. ÀÏ´Ü ¼±Çà°Ë»öÀº ¾î¶² ÁÖÀÇÇÒ ¸¸ÇÑ ¿µÇâÀ» °®´Â °ÍÀ» ¹æÁö ÇÑ´Ù..
More precisely, stringification and concatenation use the argument tokens as given without initially scanning for macros. The same argument would be used in expanded form if it is substituted elsewhere without stringification or concatenation.
Á» ´õ Á¤È®ÇÏ°Ô, stringfication ±×¸®°í ¿¬°áÀº ÀÎÀÚ ÅäÅ«µéÀº ÁÖ¾îÁø °Íó·³ ¸ÅÅ©·Î¸¦ À§ÇÑ ÃʱâÈ °Ë»ö¾øÀÌ »ç¿ëÇÑ´Ù. °°Àº ÀÎÀÚ´Â ¸¸¾à ±×°ÍÀÌ stringification ¶Ç´Â ¿¬°á ¾øÀÌ ´Ù¸¥ °÷¿¡¼ ´ëü µÈ´Ù¸é È®ÀåµÈ Çü½Ä¿¡ »ç¿ë µÉ °ÍÀÌ´Ù.
#define str(s) #s lose(s) #define foo 4 str (foo)
expands to `"foo" lose(4)'.
You might now ask, "Why mention the prescan, if it makes no difference? And why not skip it and make the preprocessor faster?" The answer is that the prescan does make a difference in three special cases:
´ç½ÅÀÌ Áö±Ý ¹°¾î º¼Áöµµ ¸ð¸£°Ú´Ù. "¿Ö ¼±Çà °Ë»ö¿¡ ´ëÇØ ¾ð±ÞÇϳª? ¸¸¾à ±×°Í¿¡ Â÷ÀÌ°¡ ¾ø´Ù¸é? ±×¸®°í ±×°ÍÀ» °Ç³Ê ¶ç¾î¼ Àü󸮱⸦ Á» ´õ ºü¸£°Ô ¸¸µå´Â °ÍÀº ¾î¶²°¡?" ´ë´äÀº ¼±Çà °Ë»öÀº ¼¼ °¡Áö Ưº°ÇÑ °æ¿ì¿¡ Â÷ÀÌÁ¡À» ¸¸µç´Ù´Â °ÍÀÌ´Ù.
We say that nested calls to a macro occur when a macro's argument contains a call to that very macro. For example, if `f' is a macro that expects one argument, `f (f (1))' is a nested pair of calls to `f'. The desired expansion is made by expanding `f (1)' and substituting that into the definition of `f'. The prescan causes the expected result to happen. Without the prescan, `f (1)' itself would be substituted as an argument, and the inner use of `f' would appear during the main scan as an indirect self-reference and would not be expanded. Here, the prescan cancels an undesirable side effect (in the medical, not computational, sense of the term) of the special rule for self-referential macros.
¿ì¸®´Â ÁßøÀº ¸ÅÅ©·ÎÀÇ ÀÎÀÚµé·Î ¸ÅÅ©·Î¸¦ È£Ãâ ÇÒ ¶§ ¹ß»ýÇÏ´Â ¸ÅÅ©·Î¶ó°í ºÎ¸¥´Ù. ¿¹¸¦ µé¾î, ¸¸¾à `f'°¡ ÇϳªÀÇ ¿¹»ó ÇÒ ¼ö ÀÖ´Â ¸ÅÅ©·Î¶ó¸é, `f (f (1))'´Â `f¿¡ Áßø È£Ãâ ½ÖÀÌ´Ù. ¹Ù¶÷Á÷ÇÑ È®ÀåÀº `f(1)È®Àå°ú `f¡¯ÀÇ Á¤ÀÇ·Î ´ëüÇÔÀ¸·Î½á ¸¸µé¾î Áø´Ù. ¼±Çà °Ë»öÀº ¿¹»óµÈ °á°ú¸¦ ¹ß»ý ½ÃŲ´Ù. ¼±Çà °Ë»öÀÌ ¾ø´Ù¸é, `f(1)¡¯Àº ±×°Í ÀÚü°¡ ÀÎÀÚ·Î½á ´ëü µÉ °ÍÀÌ°í `f¡¯ÀÇ ³»Àû »ç¿ëÀº ¸ÞÀÎ °Ë»ö µ¿¾È¿¡ °£Á¢ÀûÀÎ ÀÚ±â ÂüÁ¶·Î½á ³ªÅ¸³¯Áö ¸ð¸£°í È®Àå µÇÁö ¾ÊÀ» °ÍÀÌ´Ù. ¼±Çà °Ë»öÀº ÀÚ±â ÂüÁ¶ ¸ÅÅ©·ÎµéÀ» À§ÇÑ Æ¯º°ÇÑ ·êÀÇ ¹Ù¶÷Á÷ÇÏÁö ¾ÊÀº ºÎ°¡Àû È¿°ú¸¦ Ãë¼Ò ½ÃŲ´Ù.
Prescan causes trouble in certain other cases of nested macro calls. Here is an example:
¼±Çà°Ë»öÀº ÁßøµÈ ¸ÅÅ©·Î È£ÃâÀÇ ¾î¶² ´Ù¸¥ °æ¿ì¿¡ ¹®Á¦¸¦ ¾ß±â ½ÃŲ´Ù. ¿¹¸¦ ºÁ¶ó
#define foo a,b #define bar(x) lose(x) #define lose(x) (1 + (x)) bar(foo)
We would like `bar(foo)' to turn into `(1 + (foo))', which
would then turn into `(1 + (a,b))'. Instead, `bar(foo)'
expands into `lose(a,b)', and you get an error because lose
requires a single argument. In this case, the problem is easily solved
by the same parentheses that ought to be used to prevent misnesting of
arithmetic operations:
¿ì¸®´Â `bar(foo)`¸¦ `(1 + (foo))' ¹Ù²Ù±â¸¦ ¿øÇÑ´Ù. ±×¸®°í ´ÙÀ½¿¡ `(1 + (a,b))'Çϱ⸦ ¿øÇÑ´Ù. ´ë½Å¿¡, `bar(foo)¡¯´Â `lose(a,b)'·Î È®Àå µÈ´Ù. ±×¸®°í ´ç½ÅÀº ÇϳªÀÇ ÀÎÀÚ ¿ä±¸¸¦ ÀÒ¾ú±â ¶§¹®¿¡ ¿¡·¯¸¦ ¾ò°Ô µÈ´Ù. ÀÌ °æ¿ì, ¼öÇÐÀû ¿¬»êÀÇ À߸øµÈ ÁßøÀ» ¹æÁöÇϱâ À§Çؼ °°Àº °ýÈ£¸¦ »ç¿ëÇÔÀ¸·Î½á ½±°Ô ¹®Á¦´Â ÇØ°á µÈ´Ù.
#define foo (a,b) #define bar(x) lose((x))
The problem is more serious when the operands of the macro are not expressions; for example, when they are statements. Then parentheses are unacceptable because they would make for invalid C code:
¸ÅÅ©·ÎÀÇ ÇÇ¿¬ÀÚµéÀÌ Ç¥ÇöÀÌ ¾Æ´Ò ¶§ ¹®Á¦´Â ´õ ½É°¢ÇØÁø´Ù.; ¿¹¸¦ µé¸é ±×°ÍµéÀÌ ¹®ÀåµÑÀÏ ¶§ÀÌ´Ù. ±× ´ÙÀ½¿¡ °ýÈ£µéÀº ¹Þ¾Æ µéÀÏ ¼ö ¾ø´Ù. ¿Ö³ÄÇÏ¸é ±×°ÍÀº C Äڵ带 ¿Ã¹Ù¸£Áö ¾Ê°Ô ¸¸µé±â ¶§¹®ÀÌ´Ù.
#define foo { int a, b; ... }
In GNU C you can shield the commas using the `({...})' construct which turns a compound statement into an expression:
GNU C¿¡¼ ´ç½ÅÀº º¹ÀâÇÑ ¹®ÀÚÀ» Ç¥Çö½ÄÀ¸·Î ¹Ù²Ù´Â `({...})¡¯±¸Á¶¸¦ »ç¿ëÇؼ ÄÞ¸¶µéÀ» º¸È£ÇÒ ¼ö ÀÖ´Ù.
#define foo ({ int a, b; ... })
Or you can rewrite the macro definition to avoid such commas:
¶Ç´Â ´ç½ÅÀº ¸ÅÅ©·Î Á¤ÀǸ¦ ±×·± ÄÞ¸¶¸¦ ÇÇÇؼ ´Ù½Ã ¾µ ¼ö ÀÖ´Ù.
#define foo { int a; int b; ... }
There is also one case where prescan is useful. It is possible to use prescan to expand an argument and then stringify it -- if you use two levels of macros. Let's add a new macro `xstr' to the example shown above:
¼±Çà °Ë»öÀÌ À¯¿ëÇÑ °÷ÀÌ ¶Ç ÇÑ °æ¿ì°¡ ÀÖ´Ù. ÀÎÀÚ¸¦ È®ÀåÇÏ°í stringifyÇÏ´Â °Í¿¡ ¼±Çà󸮸¦ »ç¿ëÇÏ´Â °ÍÀÌ °¡´ÉÇÏ´Ù - ¸¸¾à ´ç½ÅÀÌ ¸ÅÅ©·ÎµéÀÇ µÎ ·¹º§À» »ç¿ëÇÑ´Ù¸é. »õ·Î¿î ¸ÅÅ©·Î `xstr'¸¦ À§ÀÇ ¿¹¿¡ ´õÇØ º¸ÀÚ.
#define xstr(s) str(s) #define str(s) #s #define foo 4 xstr (foo)
This expands into `"4"', not `"foo"'. The reason for the difference is that the argument of `xstr' is expanded at prescan (because `xstr' does not specify stringification or concatenation of the argument). The result of prescan then forms the argument for `str'. `str' uses its argument without prescan because it performs stringification; but it cannot prevent or undo the prescanning already done by `xstr'.
ÀÌ È®ÀåÀº `"foo"'°¡ ¾Æ´Ï¶ó `"4"'·Î È®Àå µÈ´Ù. Â÷ÀÌÁ¡¿¡ ÀÌÀ¯´Â `xstr`ÀÇ ÀÎÀÚ´Â ¼±Çà°Ë»ö¿¡¼ È®ÀåµÈ °ÍÀÌ ¶§¹®ÀÌ´Ù( ¿Ö³ÄÇϸé `xstr¡¯Àº ÀÎÀÚÀÇstringification ¶Ç´Â concatenationÀ» ±¸Ã¼ÈÇÏÁö ¾Ê±â ¶§¹®ÀÌ´Ù.). ¼±Çà °Ë»öÀÇ °á°ú´Â `str¡¯À» À§ÇÑ ÀÎÀÚ·Î Çü½ÄÈ µÈ´Ù. `str¡¯Àº ¼±Çà °Ë»ö ¾øÀÌ ±×°ÍÀÇ ÀÎÀÚ¸¦ »ç¿ëÇÑ´Ù. ¿Ö³ÄÇÏ¸é ±×°ÍÀº stringficationÀ» ¼öÇàÇϱ⠶§¹®ÀÌ´Ù; ±×·¯³ª `xstr¡¯·Î ÀÌ¹Ì ³¡³½ ¼±Çà°Ë»ö ÇÏ´Â °ÍÀ» µÇµ¹¸®°Å³ª ¸·À» ¼ö´Â ¾ø´Ù.
A cascade of macros is when one macro's body contains a reference to another macro. This is very common practice. For example,
¸ÅÅ©·ÎÀÇcascade´Â ÇÑ ¸ÅÅ©·ÎÀÇ ¸öä°¡ ´Ù¸¥ ¸ÅÅ©·Î¿¡ ÂüÁ¶¸¦ Æ÷ÇÔÇÒ ¶§ ÀÌ´Ù. ÀÌ°ÍÀº ¸Å¿ì ÈçÇÑ ¿¬½ÀÀÌ´Ù. ¿¹¸¦ º¸¸é,
#define BUFSIZE 1020 #define TABLESIZE BUFSIZE
This is not at all the same as defining `TABLESIZE' to be `1020'. The `#define' for `TABLESIZE' uses exactly the body you specify -- in this case, `BUFSIZE' -- and does not check to see whether it too is the name of a macro.
ÀÌ°ÍÀº 'TABLESIZE'¸¦ `1020'·Î µÇ°Ô Á¤ÀÇ ÇÏ´Â °Í°ú ÀüÇô °°Áö ¾Ê´Ù. `TABLESIZE'À» À§ÇÑ `#define¡¯´Â Á¤È®ÇÏ°Ô ´ç½ÅÀÌ ±¸Ã¼ÈÇÑ ¸öü¿¡ »ç¿ëÇÑ´Ù?ÀÌ °æ¿ì, `BUFSIZE¡¯?±×¸®°í ±×°ÍÀÌ ¸ÅÅ©·ÎÀÇ À̸§ÀÎÁö ¾Æ´ÑÁö º¸±âÀ§ÇØ Ã¼Å©ÇÏÁö ¾Ê´Â´Ù
It's only when you use `TABLESIZE' that the result of its expansion is checked for more macro names.
È®ÀåÀÇ °á°ú°¡ Á»´õ ¸ÅÅ©·Î À̸§µéÀ» À§ÇØ Ã¼Å©µÇ´Â °ÍÀº ´ç½ÅÀÌ `TABLESIZE'¸¦ »ç¿ëÇÒ ¶§ ¸¸ÀÌ´Ù
This makes a difference if you change the definition of `BUFSIZE' at some point in the source file. `TABLESIZE', defined as shown, will always expand using the definition of `BUFSIZE' that is currently in effect:
¸¸¾à ´ç½ÅÀÌ ¼Ò½º ÆÄÀÏÀÇ °°Àº ÁöÁ¡¿¡¼ `BUFSIZE'ÀÇ Á¤ÀǸ¦ ¹Ù²Û´Ù¸é ÀÌ°ÍÀº Â÷ÀÌÁ¡À» ¸¸µé´Ù.`TABLESIZE'´Â Ç×»ó ÇöÀç È¿·ÂÀ» °®°í ÀÖ´Â`BUFSIZE'ÀÇ Á¤ÀǸ¦ ÀÌ¿ëÇؼ È®ÀåÇÒ °ÍÀÌ´Ù.
#define BUFSIZE 1020 #define TABLESIZE BUFSIZE #undef BUFSIZE #define BUFSIZE 37
Now `TABLESIZE' expands (in two stages) to `37'. (The
`#undef' is to prevent any warning about the nontrivial
redefinition of BUFSIZE
.)
Áö±Ý `TABLESIZE'´Â ( µÑ° ´Ü°è¿¡¼) `37'·Î È®Àå µÈ´Ù. ( `#undef' ´Â BUFSIZEÀÇ ÇÏÂúÁö ¾ÊÀº ÀçÁ¤ÀÇ¿¡ ´ëÇÑ ¾î¶² °æ°íµµ ¹æÁöÇÒ ¼ö ÀÖ´Ù.)
The invocation of a function-like macro can extend over many logical lines. The ISO C standard requires that newlines within a macro invocation be treated as ordinary whitespace. This means that when the expansion of a function-like macro replaces its invocation, it appears on the same line as the macro name did. Thus line numbers emitted by the compiler or debugger refer to the line the invocation started on, which might be different to the line containing the argument causing the problem.
function-like ¸ÅÅ©·ÎÀÇ ¼ÒȯÀº ¸¹Àº ³í¸® ¶óÀεéÀ» È®ÀåÇÑ´Ù. ISO C Ç¥ÁØÀº ¸ÅÅ©·Î ¼Òȯ ³»¿¡¼ »õ·Î¿î ¶óÀεéÀº º¸Åë °ø¹éÀ¸·Î½á ´Ù·çµµ·Ï ¿ä±¸ ÇÑ´Ù. ÀÌ°ÍÀÌ ÀǹÌÇÏ´Â °ÍÀº fuction-like ¸ÅÅ©·ÎÀÇ È®ÀåÀº ±×°ÍÀÇ ¼ÒȯÀ» ±³Ã¼ÇÒ ¶§, ¸ÅÅ©·Î À̸§ÀÌ ÇÏ´Â °Íó·³ °°Àº ¶óÀο¡ ³ªÅ¸³´Ù´Â °ÍÀÌ´Ù. °Ô´Ù°¡ ¶óÀÎÀÇ ³Ñ¹öµéÀº ÄÄÆÄÀÏ·¯³ª µð¹ö°Å°¡ ¼ÒȯÀÌ ½ÃÀÛÇÏ´Â ¶óÀÎÀ» »ý°¢ÇÏ´Â °ÍÀ» Çã¿ëÇÑ´Ù. ±×¸®°í ¹®Á¦¸¦ ¾ß±âÇÏ´Â ÀÎÀÚµéÀ» Æ÷ÇÔÇÑ ¶óÀΰúÀÇ Â÷ÀÌ°¡ µÉ °ÍÀÌ´Ù.
Here is an example illustrating this:
¿©±â ¼³¸íÇÏ´Â ¿¹°¡ ÀÖ´Ù.:
#define ignore_second_arg(a,b,c) a; c ignore_second_arg (foo (), ignored (), syntax error);
The syntax error triggered by the tokens `syntax error' results in an error message citing line three -- the line of ignore_second_arg --- even though the problematic code comes from line five.
`sytax error' ÅäÅ«¿¡ ÀÇÇØ ½ÃÀÛµÈ ÀÌ ¹®¹ý ¿¡·¯´Â ¶óÀÎ 5¿¡ ¹®Á¦ Äڵ尡 À־ ¶óÀÎ 3( ignore_second_arg¿¡ ¶óÀÎ )¿¡¼ º¸°íµÈ ¿¡·¯ ¸Þ½ÃÁö¸¦ °á°ú·Î ³½´Ù.
In a macro processor, a conditional is a directive that allows a part of the program to be ignored during compilation, on some conditions. In the C preprocessor, a conditional can test either an arithmetic expression or whether a name is defined as a macro.
A conditional in the C preprocessor resembles in some ways an `if' statement in C, but it is important to understand the difference between them. The condition in an `if' statement is tested during the execution of your program. Its purpose is to allow your program to behave differently from run to run, depending on the data it is operating on. The condition in a preprocessing conditional directive is tested when your program is compiled. Its purpose is to allow different code to be included in the program depending on the situation at the time of compilation.
Generally there are three kinds of reason to use a conditional.
Most simple programs that are intended to run on only one machine will not need to use preprocessing conditionals.
A conditional in the C preprocessor begins with a conditional directive: `#if', `#ifdef' or `#ifndef'. See section Conditionals and Macros, for information on `#ifdef' and `#ifndef'; only `#if' is explained here.
The `#if' directive in its simplest form consists of
#if expression controlled text #endif /* expression */
The comment following the `#endif' is not required, but it is a good practice because it helps people match the `#endif' to the corresponding `#if'. Such comments should always be used, except in short conditionals that are not nested. In fact, you can put anything at all after the `#endif' and it will be ignored by the GNU C preprocessor, but only comments are acceptable in ISO Standard C.
expression is a C expression of integer type, subject to stringent restrictions. It may contain
long
or
unsigned long
.
Note that `sizeof' operators and enum
-type values are not
allowed. enum
-type values, like all other identifiers that are
not taken as macro calls and expanded, are treated as zero.
The controlled text inside of a conditional can include preprocessing directives. Then the directives inside the conditional are obeyed only if that branch of the conditional succeeds. The text can also contain other conditional groups. However, the `#if' and `#endif' directives must balance.
The `#else' directive can be added to a conditional to provide alternative text to be used if the condition is false. This is what it looks like:
#if expression text-if-true #else /* Not expression */ text-if-false #endif /* Not expression */
If expression is nonzero, and thus the text-if-true is active, then `#else' acts like a failing conditional and the text-if-false is ignored. Conversely, if the `#if' conditional fails, the text-if-false is considered included.
One common case of nested conditionals is used to check for more than two possible alternatives. For example, you might have
#if X == 1 ... #else /* X != 1 */ #if X == 2 ... #else /* X != 2 */ ... #endif /* X != 2 */ #endif /* X != 1 */
Another conditional directive, `#elif', allows this to be abbreviated as follows:
#if X == 1 ... #elif X == 2 ... #else /* X != 2 and X != 1*/ ... #endif /* X != 2 and X != 1*/
`#elif' stands for "else if". Like `#else', it goes in the middle of a `#if'-`#endif' pair and subdivides it; it does not require a matching `#endif' of its own. Like `#if', the `#elif' directive includes an expression to be tested.
The text following the `#elif' is processed only if the original `#if'-condition failed and the `#elif' condition succeeds. More than one `#elif' can go in the same `#if'-`#endif' group. Then the text after each `#elif' is processed only if the `#elif' condition succeeds after the original `#if' and any previous `#elif' directives within it have failed. `#else' is equivalent to `#elif 1', and `#else' is allowed after any number of `#elif' directives, but `#elif' may not follow `#else'.
If you replace or delete a part of the program but want to keep the old code around as a comment for future reference, the easy way to do this is to put `#if 0' before it and `#endif' after it. This is better than using comment delimiters `/*' and `*/' since those won't work if the code already contains comments (C comments do not nest).
This works even if the code being turned off contains conditionals, but they must be entire conditionals (balanced `#if' and `#endif').
Conversely, do not use `#if 0' for comments which are not C code. Use the comment delimiters `/*' and `*/' instead. The interior of `#if 0' must consist of complete tokens; in particular, single-quote characters must balance. Comments often contain unbalanced single-quote characters (known in English as apostrophes). These confuse `#if 0'. They do not confuse `/*'.
Conditionals are useful in connection with macros or assertions, because those are the only ways that an expression's value can vary from one compilation to another. A `#if' directive whose expression uses no macros or assertions is equivalent to `#if 1' or `#if 0'; you might as well determine which one, by computing the value of the expression yourself, and then simplify the program.
For example, here is a conditional that tests the expression `BUFSIZE == 1020', where `BUFSIZE' must be a macro.
#if BUFSIZE == 1020 printf ("Large buffers!\n"); #endif /* BUFSIZE is large */
(Programmers often wish they could test the size of a variable or data
type in `#if', but this does not work. The preprocessor does not
understand sizeof
, or typedef names, or even the type keywords
such as int
.)
The special operator `defined' is used in `#if' and `#elif' expressions to test whether a certain name is defined as a macro. Either `defined name' or `defined (name)' is an expression whose value is 1 if name is defined as macro at the current point in the program, and 0 otherwise. To the `defined' operator it makes no difference what the definition of the macro is; all that matters is whether there is a definition. Thus, for example,
#if defined (vax) || defined (ns16000)
would succeed if either of the names `vax' and `ns16000' is defined as a macro. You can test the same condition using assertions (see section Assertions), like this:
#if #cpu (vax) || #cpu (ns16000)
If a macro is defined and later undefined with `#undef', subsequent use of the `defined' operator returns 0, because the name is no longer defined. If the macro is defined again with another `#define', `defined' will recommence returning 1.
If the `defined' operator appears as a result of a macro expansion, the C standard says the behavior is undefined. GNU cpp treats it as a genuine `defined' operator and evaluates it normally. It will warn wherever your code uses this feature if you use the command-line option `-pedantic', since other compilers may handle it differently.
Conditionals that test whether a single macro is defined are very common, so there are two special short conditional directives for this case.
#ifdef name
#ifndef name
Macro definitions can vary between compilations for several reasons.
The directive `#error' causes the preprocessor to report a fatal error. The tokens forming the rest of the line following `#error' are used as the error message, and not macro-expanded. Internal whitespace sequences are each replaced with a single space. The line must consist of complete tokens.
You would use `#error' inside of a conditional that detects a combination of parameters which you know the program does not properly support. For example, if you know that the program will not run properly on a Vax, you might write
#ifdef __vax__ #error "Won't work on Vaxen. See comments at get_last_object." #endif
See section Nonstandard Predefined Macros, for why this works.
If you have several configuration parameters that must be set up by the installation in a consistent way, you can use conditionals to detect an inconsistency and report it with `#error'. For example,
#if HASH_TABLE_SIZE % 2 == 0 || HASH_TABLE_SIZE % 3 == 0 \ || HASH_TABLE_SIZE % 5 == 0 #error HASH_TABLE_SIZE should not be divisible by a small prime #endif
The directive `#warning' is like the directive `#error', but causes the preprocessor to issue a warning and continue preprocessing. The tokens following `#warning' are used as the warning message, and not macro-expanded.
You might use `#warning' in obsolete header files, with a message directing the user to the header file which should be used instead.
Assertions are a more systematic alternative to macros in writing conditionals to test what sort of computer or system the compiled program will run on. Assertions are usually predefined, but you can define them with preprocessing directives or command-line options.
The macros traditionally used to describe the type of target are not classified in any way according to which question they answer; they may indicate a hardware architecture, a particular hardware model, an operating system, a particular version of an operating system, or specific configuration options. These are jumbled together in a single namespace. In contrast, each assertion consists of a named question and an answer. The question is usually called the predicate. An assertion looks like this:
#predicate (answer)
You must use a properly formed identifier for predicate. The value of answer can be any sequence of words; all characters are significant except for leading and trailing whitespace, and differences in internal whitespace sequences are ignored. (This is similar to the rules governing macro redefinition.) Thus, `x + y' is different from `x+y' but equivalent to ` x + y '. `)' is not allowed in an answer.
Here is a conditional to test whether the answer answer is asserted for the predicate predicate:
#if #predicate (answer)
There may be more than one answer asserted for a given predicate. If you omit the answer, you can test whether any answer is asserted for predicate:
#if #predicate
Most of the time, the assertions you test will be predefined assertions.
GNU C provides three predefined predicates: system
, cpu
,
and machine
. system
is for assertions about the type of
software, cpu
describes the type of computer architecture, and
machine
gives more information about the computer. For example,
on a GNU system, the following assertions would be true:
#system (gnu) #system (mach) #system (mach 3) #system (mach 3.subversion) #system (hurd) #system (hurd version)
and perhaps others. The alternatives with more or less version information let you ask more or less detailed questions about the type of system software.
On a Unix system, you would find #system (unix)
and perhaps one of:
#system (aix)
, #system (bsd)
, #system (hpux)
,
#system (lynx)
, #system (mach)
, #system (posix)
,
#system (svr3)
, #system (svr4)
, or #system (xpg4)
with possible version numbers following.
Other values for system
are #system (mvs)
and #system (vms)
.
Portability note: Many Unix C compilers provide only one answer
for the system
assertion: #system (unix)
, if they support
assertions at all. This is less than useful.
An assertion with a multi-word answer is completely different from several
assertions with individual single-word answers. For example, the presence
of system (mach 3.0)
does not mean that system (3.0)
is true.
It also does not directly imply system (mach)
, but in GNU C, that
last will normally be asserted as well.
The current list of possible assertion values for cpu
is:
#cpu (a29k)
, #cpu (alpha)
, #cpu (arm)
, #cpu
(clipper)
, #cpu (convex)
, #cpu (elxsi)
, #cpu
(tron)
, #cpu (h8300)
, #cpu (i370)
, #cpu (i386)
,
#cpu (i860)
, #cpu (i960)
, #cpu (m68k)
, #cpu
(m88k)
, #cpu (mips)
, #cpu (ns32k)
, #cpu (hppa)
,
#cpu (pyr)
, #cpu (ibm032)
, #cpu (rs6000)
,
#cpu (sh)
, #cpu (sparc)
, #cpu (spur)
, #cpu
(tahoe)
, #cpu (vax)
, #cpu (we32000)
.
You can create assertions within a C program using `#assert', like this:
#assert predicate (answer)
(Note the absence of a `#' before predicate.)
Each time you do this, you assert a new true answer for predicate. Asserting one answer does not invalidate previously asserted answers; they all remain true. The only way to remove an answer is with `#unassert'. `#unassert' has the same syntax as `#assert'. You can also remove all answers to a predicate like this:
#unassert predicate
You can also add or cancel assertions using command options
when you run gcc
or cpp
. See section Invoking the C Preprocessor.
One of the jobs of the C preprocessor is to inform the C compiler of where each line of C code came from: which source file and which line number.
C code can come from multiple source files if you use `#include'; both `#include' and the use of conditionals and macros can cause the line number of a line in the preprocessor output to be different from the line's number in the original source file. You will appreciate the value of making both the C compiler (in error messages) and symbolic debuggers such as GDB use the line numbers in your source file.
The C preprocessor builds on this feature by offering a directive by
which you can control the feature explicitly. This is useful when a
file for input to the C preprocessor is the output from another program
such as the bison
parser generator, which operates on another
file that is the true source file. Parts of the output from
bison
are generated from scratch, other parts come from a
standard parser file. The rest are copied nearly verbatim from the
source file, but their line numbers in the bison
output are not
the same as their original line numbers. Naturally you would like
compiler error messages and symbolic debuggers to know the original
source file and line number of each line in the bison
input.
bison
arranges this by writing `#line' directives into the output
file. `#line' is a directive that specifies the original line number
and source file name for subsequent input in the current preprocessor input
file. `#line' has three variants:
#line linenum
#line linenum filename
#line anything else
`#line' directives alter the results of the `__FILE__' and `__LINE__' predefined macros from that point on. See section Standard Predefined Macros.
The output of the preprocessor (which is the input for the rest of the compiler) contains directives that look much like `#line' directives. They start with just `#' instead of `#line', but this is followed by a line number and file name as in `#line'. See section C Preprocessor Output.
This section describes some additional, rarely used, preprocessing directives.
The ISO standard specifies that the effect of the `#pragma' directive is implementation-defined. The GNU C preprocessor recognizes some pragmas, and passes unrecognized ones through to the preprocessor output, so they are available to the compilation pass.
In line with the C99 standard, which introduces a STDC namespace for C99 pragmas, the preprocessor introduces a GCC namespace for GCC pragmas. Supported GCC preprocessor pragmas are of the form `#pragma GCC ...'. For backwards compatibility previously supported pragmas are also recognized without the `GCC' prefix, however that use is deprecated. Pragmas that are already deprecated are not recognized with a `GCC' prefix.
The `#pragma GCC dependency' allows you to check the relative dates of the current file and another file. If the other file is more recent than the current file, a warning is issued. This is useful if the include file is derived from the other file, and should be regenerated. The other file is searched for using the normal include search path. Optional trailing text can be used to give more information in the warning message.
#pragma GCC dependency "parse.y" #pragma GCC dependency "/usr/include/time.h" rerun /path/to/fixincludes
The C99 standard also introduces the `_Pragma' operator. The
syntax is _Pragma (string-literal)
, where `string-literal'
can be either a normal or wide-character string literal. It is
destringized, by replacing all `\\' with a single `\' and all
`\"' with a `"'. The result is then processed as if it had
appeared as the right hand side of a `#pragma' directive. For
example,
_Pragma ("GCC dependency \"parse.y\"")
has the same effect as `#pragma GCC dependency "parse.y"'. The same effect could be achieved using macros, for example
#define DO_PRAGMA(x) _Pragma (#x) DO_PRAGMA (GCC dependency "parse.y")
The standard is unclear on where a `_Pragma' operator can appear. The preprocessor accepts it even within a preprocessing conditional directive like `#if'. To be safe, you are probably best keeping it out of directives other than `#define', and putting it on a line of its own.
The `#ident' directive is supported for compatibility with certain other systems. It is followed by a line of text. On some systems, the text is copied into a special place in the object file; on most systems, the text is ignored and this directive has no effect. Typically `#ident' is only used in header files supplied with those systems where it is meaningful.
The null directive consists of a `#' followed by a newline, with only whitespace (including comments) in between. A null directive is understood as a preprocessing directive but has no effect on the preprocessor output. The primary significance of the existence of the null directive is that an input line consisting of just a `#' will produce no output, rather than a line of output containing just a `#'. Supposedly some old C programs contain such lines.
The output from the C preprocessor looks much like the input, except that all preprocessing directive lines have been replaced with blank lines and all comments with spaces.
The ISO standard specifies that it is implementation defined whether a preprocessor preserves whitespace between tokens, or replaces it with e.g. a single space. In the GNU C preprocessor, whitespace between tokens is collapsed to become a single space, with the exception that the first token on a non-directive line is preceded with sufficient spaces that it appears in the same column in the preprocessed output that it appeared in in the original source file. This is so the output is easy to read. See section Undefined Behavior and Deprecated Features.
Source file name and line number information is conveyed by lines of the form
# linenum filename flags
which are inserted as needed into the output (but never within a string or character constant), and in place of long sequences of empty lines. Such a line means that the following line originated in file filename at line linenum.
After the file name comes zero or more flags, which are `1', `2', `3', or `4'. If there are multiple flags, spaces separate them. Here is what the flags mean:
The ISO C standard mandates that implementations document various aspects of preprocessor behavior. You should try to avoid undue reliance on behaviour described here, as it is possible that it will change subtly in future implementations.
The following documents internal limits of GNU cpp.
This section details GNU C preprocessor behavior that is subject to change or deprecated. You are strongly advised to write your software so it does not rely on anything described here; future versions of the preprocessor may subtly change such behavior or even remove the feature altogether.
Preservation of the form of whitespace between tokens is unlikely to change from current behavior (section C Preprocessor Output), but you are advised not to rely on it.
The following are undocumented and subject to change:-
The following features are in flux and should not be used in portable code:
#define debug(format, ...) printf (format, __VA_ARGS__) debug("string"); /* Not permitted by C standard. */ debug("string",); /* OK. */This extension will be preserved, but the special behavior of `##' in this context has changed in the past and may change again in the future.
The following features are deprecated and will likely be removed at some point in the future:-
Most often when you use the C preprocessor you will not have to invoke it explicitly: the C compiler will do so automatically. However, the preprocessor is sometimes useful on its own.
The C preprocessor expects two file names as arguments, infile and outfile. The preprocessor reads infile together with any other files it specifies with `#include'. All the output generated by the combined input files is written in outfile.
Either infile or outfile may be `-', which as infile means to read from standard input and as outfile means to write to standard output. Also, if either file is omitted, it means the same as if `-' had been specified for that file.
Here is a table of command options accepted by the C preprocessor. These options can also be given when compiling a C program; they are passed along automatically to the preprocessor when it is invoked by the compiler.
C This isn't an unterminated character constant C Neither is "20000000000, an octal constant C in some dialects of FortranHowever, this type of comment line will likely produce a diagnostic, or at least unexpected output from the preprocessor, due to the unterminated comment:
C Some Fortran compilers accept /* as starting C an inline comment.Note that
g77
automatically supplies the `-traditional'
option when it invokes the preprocessor. However, a future version of
g77
might use a different, more-Fortran-aware preprocessor in
place of cpp
.
touch foo.h; cpp -dM foo.hwill show the values of any predefined macros.
make
describing the dependencies of the main source
file. The preprocessor outputs one make
rule containing the
object file name for that source file, a colon, and the names of all the
included files. If there are many included files then the rule is split
into several lines using `\'-newline.
`-MG' says to treat missing header files as generated files and
assume they live in the same directory as the source file. It must be
specified in addition to `-M'.
This feature is used in automatic updating of makefiles.
gcc
, do not specify the file argument.
gcc
will create file names made by replacing ".c" with ".d" at
the end of the input file names.
In Mach, you can use the utility md
to merge multiple dependency
files into a single dependency file suitable for using with the
`make' command.
iso9899:1990
c89
iso9899:199409
iso9899:1999
c99
iso9899:199x
c9x
gnu89
gnu99
gnu9x
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