C Compiler Characteristics

The following macros check for C compiler or machine architecture features. To check for characteristics not listed here, use AC_TRY_COMPILE (see section Examining Syntax) or AC_TRY_RUN (see section Checking Run Time Behavior)

Macro: AC_C_BIGENDIAN

If words are stored with the most significant byte first (like Motorola and SPARC, but not Intel and VAX, CPUs), define WORDS_BIGENDIAN.

Macro: AC_C_CONST

If the C compiler does not fully support the keyword const, define const to be empty. Some C compilers that do not define __STDC__ do support const; some compilers that define __STDC__ do not completely support const. Programs can simply use const as if every C compiler supported it; for those that don't, the `Makefile' or configuration header file will define it as empty.

Macro: AC_C_INLINE

If the C compiler supports the keyword inline, do nothing. Otherwise define inline to __inline__ or __inline if it accepts one of those, otherwise define inline to be empty.

Macro: AC_C_CHAR_UNSIGNED

If the C type char is unsigned, define __CHAR_UNSIGNED__, unless the C compiler predefines it.

Macro: AC_C_LONG_DOUBLE

If the C compiler supports the long double type, define HAVE_LONG_DOUBLE. Some C compilers that do not define __STDC__ do support the long double type; some compilers that define __STDC__ do not support long double.

Macro: AC_C_STRINGIZE

If the C preprocessor supports the stringizing operator, define HAVE_STRINGIZE. The stringizing operator is `#' and is found in macros such as this:

#define x(y) #y

Macro: AC_CHECK_SIZEOF (type [, cross-size])

Define SIZEOF_uctype to be the size in bytes of the C (or C++) builtin type type, e.g. `int' or `char *'. If `type' is unknown to the compiler, it gets a size of 0. uctype is type, with lowercase converted to uppercase, spaces changed to underscores, and asterisks changed to `P'. If cross-compiling, the value cross-size is used if given, otherwise configure exits with an error message.

For example, the call

AC_CHECK_SIZEOF(int *)

defines SIZEOF_INT_P to be 8 on DEC Alpha AXP systems.

Macro: AC_INT_16_BITS

If the C type int is 16 bits wide, define INT_16_BITS. This macro is obsolete; it is more general to use `AC_CHECK_SIZEOF(int)' instead.

Macro: AC_LONG_64_BITS

If the C type long int is 64 bits wide, define LONG_64_BITS. This macro is obsolete; it is more general to use `AC_CHECK_SIZEOF(long)' instead.

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