安全三原则是指什么

• C90
• C99
• C11
• C17
• C23
• C2y

C2y Support in GCC

C2y can be explicitly selected with the -std=c2y command-line flag, or -std=gnu2y to enable GNU extensions as well.

C23 Support in GCC

C23 mode is the default since GCC 15; it can be explicitly selected with the -std=c23 command-line flag, or -std=gnu23 to enable GNU extensions as well.

C17 Support in GCC

C17 can be explicitly selected with the -std=c17 command-line flag, or -std=gnu17 to enable GNU extensions as well.

This was the default mode from GCC 8 to GCC 14 (including).

C11 Support in GCC

C11 can be explicitly selected with the -std=c11 command-line flag, or -std=gnu11 to enable GNU extensions as well.

C99 Support in GCC

C99 is substantially completely supported as of GCC 4.5 (with -std=c99 -pedantic-errors used; -fextended-identifiers also needed to enable extended identifiers before GCC 5), modulo bugs and floating-point issues (mainly but not entirely relating to optional C99 features from Annexes F and G). The following table gives more details of the C99 support in different GCC versions.

This table is based on the list in the foreword to N1256 (ISO/IEC 9899:1999 (E), consolidated with ISO/IEC 9899:1999/Cor.1:2001 (E), ISO/IEC 9899:1999/Cor.2:2004 (E) and ISO/IEC 9899:1999/Cor.3:2007 (E)).

The "Version" column indicates the first GCC version in which support for the relevant feature was substantially present; some bugs or corner cases may have been fixed in later versions; this column is "N/A" if nothing is needed from the compiler for the feature to be substantially supported (for example, if the feature refers to addition of new library functions rather than language features), even if additional compiler features could be useful in conjunction with it. It is assumed that GCC is used with -std=c99 -pedantic-errors (for versions 3.0 and later), as well as -fextended-identifiers in the case of that feature before GCC 5. Where library cooperation is required, it is assumed that a recent version of the GNU C Library is in use, and support with other C libraries may be less good. Where the version listed is before GCC 3.0, it should not be assumed that all corner cases follow C99 before GCC 3.0, even if there is no specific note regarding corner cases.

See below the table for further notes on some issues.

C90 Support in GCC

Further notes

• cpp has limited support for multibyte character sets.
• IEC 60559 is IEEE 754 floating point. This works if and only if the hardware is perfectly compliant, but GCC does not define __STDC_IEC_559__ or implement the associated standard pragmas; nor do some options such as -frounding-math to enable the pragmas globally work in all cases (for example, required exceptions may not be generated) and contracting expressions (e.g., using fused multiply-add) is not restricted to source-language expressions as required by C99.
• For thorough support of math_errhandling the compiler needs to mark its output from compilations using -fno-trapping-math or -fno-math-errno, possibly using the .gnu_attribute mechanism, to indicate that built-in function optimizations may have been applied that mean that not all calls report error status in a particular way; the static linker needs to put this information in executables and shared libraries and the C library needs to use it to set math_errhandling at startup to a conservatively correct value based on the information from the compiler. There is currently some limited GNU C Library support that only conforms as long as the above options are not used anywhere in the program.
• const-qualified compound literals could share storage with each other and with string literals, but currently don't.
• The information provided by static in parameter array declarators is not used for optimization. It might make sense to use it in future in conjunction with work on prefetching.