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C 표준, GCC 그리고 컴파일 옵션

GCC supports three versions of the C standard, although support for the most recent version is not yet complete.

The original ANSI C standard (X3.159-1989) was ratified in 1989 and published in 1990. This standard was ratified as an ISO standard (ISO/IEC 9899:1990) later in 1990. There were no technical differences between these publications, although the sections of the ANSI standard were renumbered and became clauses in the ISO standard. This standard, in both its forms, is commonly known as C89, or occasionally as C90, from the dates of ratification. The ANSI standard, but not the ISO standard, also came with a Rationale document. To select this standard in GCC, use one of the options -ansi-std=c90 or -std=iso9899:1990; to obtain all the diagnostics required by the standard, you should also specify -pedantic (or -pedantic-errors if you want them to be errors rather than warnings). See Options Controlling C Dialect.
Errors in the 1990 ISO C standard were corrected in two Technical Corrigenda published in 1994 and 1996. GCC does not support the uncorrected version.

An amendment to the 1990 standard was published in 1995. This amendment added digraphs and __STDC_VERSION__ to the language, but otherwise concerned the library. This amendment is commonly known as AMD1; the amended standard is sometimes known as C94 or C95. To select this standard in GCC, use the option -std=iso9899:199409 (with, as for other standard versions, -pedantic to receive all required diagnostics).

A new edition of the ISO C standard was published in 1999 as ISO/IEC 9899:1999, and is commonly known as C99. GCC has incomplete support for this standard version; see http://gcc.gnu.org/c99status.html for details. To select this standard, use -std=c99 or -std=iso9899:1999. (While in development, drafts of this standard version were referred to as C9X.)
Errors in the 1999 ISO C standard were corrected in three Technical Corrigenda published in 2001, 2004 and 2007. GCC does not support the uncorrected version.

A fourth version of the C standard, known as C11, was published in 2011 as ISO/IEC 9899:2011.  GCC has limited incomplete support for parts of this standard, enabled with -std=c11 or -std=iso9899:2011. (While in development, drafts of this standard version were referred to as C1X.)

By default, GCC provides some extensions to the C language that on rare occasions conflict with the C standard. See Extensions to the C Language Family. Use of the -std options listed above will disable these extensions where they conflict with the C standard version selected. You may also select an extended version of the C language explicitly with -std=gnu90 (for C90 with GNU extensions), -std=gnu99 (for C99 with GNU extensions) or -std=gnu11 (for C11 with GNU extensions). The default, if no C language dialect options are given, is -std=gnu90; this will change to -std=gnu99 or -std=gnu11 in some future release when the C99 or C11 support is complete. Some features that are part of the C99 standard are accepted as extensions in C90 mode, and some features that are part of the C11 standard are accepted as extensions in C90 and C99 modes.



[출처] http://gcc.gnu.org/onlinedocs/gcc/Standards.html

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() (괄호) [] (배열) -> (포인터멤버) . (구조체멤버) ! (부정) ~ (1의보수) ++ (증가) -- (감소) - (부호)  + (부호)  (자료형) (형변환)  * (포인터)  & (주소)  sizeof * (곱셈) / (나눗셈) % (나머지) + (덧셈) - (뺄셈) << >> (비트이동) < <= > >= (관계) == != (관계) & (비트논리곱) ^ (비트배타논리합) | ( 비트논리합 ) && (논리곱) || (논리합) ?: (조건) = (할당) += -= *= /= %= &= ^= |= <<= >>= (복합할당) , (쉼표)

errno.h

errno.h 파일에는 오류 코드를 기억할 수 있는 errno가 매크로로 정의되어 있고, 그 외에 각종 오류 코드 넘버들이 매크로 상수로 정의되어 있다. 프로그램 시작시에는 errno의 값이 0으로 초기화되며, 특정 오류가 발생한 때에는 이 값이 해당 오류 코드로 바뀐다. 프로그램에서도 이 값을 읽거나 수정할 수 있다. #include   <stdio.h> #include   <errno.h> int   main () {           printf ( "%d\n"   , errno);        errno = ENOMEM;           printf ( "%d\n"   , errno);           return   0; }