7.6.3 Options for Controlling the C Dialect

Table 7-7. C Dialect Control Options
Option	Definition
`-ansi`	Support all (and only) ANSI-standard C programs.
`-aux-info filename`	Output to the given file name prototype declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (`I`, `N` for new or `O` for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (`C` or `F`, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration.
`-menable-fixed[=rounding mode]`	Enable fixed-point variable types and arithmetic operation support. Optionally, set the default `rounding mode` to one of truncation, conventional, or convergent. If the `rounding mode` is not specified, the default is truncation.
`-ffreestanding`	Assert that compilation takes place in a freestanding  environment. This implies `-fno-builtin`. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at main. The most obvious example is an OS kernel. This is equivalent to `-fno-hosted`.
`-fno-asm`	Will not recognize `asm`, `inline` or `typeof` as a keyword, so that code can use these words as identifiers. You can use the keywords `__asm__`, `__inline__` and `__typeof__` instead. `-ansi` implies `-fno-asm`.
`-fno-builtin` `-fno-builtin-function`	Will not recognize built-in functions that do not begin with `__builtin_` as prefix.
`-fsigned-char`	Let the type `char` be signed, like `signed char`. (This is the default.)
`-fsigned-bitfields` `-funsigned-bitfields` `-fno-signed-bitfields` `-fno-unsigned-bitfields`	These options control whether a bit-field is signed or unsigned, when the declaration does not use either signed or unsigned. By default, such a bit-field is signed, unless `-traditional` is used, in which case bit-fields are always unsigned.
`-funsigned-char`	Let the type `char` be unsigned, like `unsigned char`.

-ansi

Support all (and only) ANSI-standard C programs.

-aux-info
                                    filename

Output to the given file name prototype declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (I, N for new or O for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration.

-menable-fixed[=rounding
                                mode]

Enable fixed-point variable types and arithmetic operation support. Optionally, set the default rounding mode to one of truncation, conventional, or convergent. If the rounding mode is not specified, the default is truncation.

-ffreestanding

Assert that compilation takes place in a freestanding  environment. This implies -fno-builtin. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at main. The most obvious example is an OS kernel. This is equivalent to -fno-hosted.

-fno-asm

Will not recognize asm, inline or typeof as a keyword, so that code can use these words as identifiers. You can use the keywords __asm__, __inline__ and __typeof__ instead.

-ansi implies -fno-asm.

-fno-builtin

-fno-builtin-function

Will not recognize built-in functions that do not begin with __builtin_ as prefix.

-fsigned-char

Let the type char be signed, like signed char. (This is the default.)

-fsigned-bitfields

-funsigned-bitfields

-fno-signed-bitfields

-fno-unsigned-bitfields

These options control whether a bit-field is signed or unsigned, when the declaration does not use either signed or unsigned. By default, such a bit-field is signed, unless -traditional is used, in which case bit-fields are always unsigned.

-funsigned-char

Let the type char be unsigned, like unsigned char.