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(autocf21.info.gz) C Compiler Characteristics

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 4.7 C Compiler Characteristics
 ==============================
 
 The following macros check for C compiler or machine architecture
 features.  To check for characteristics not listed here, use
 Time::)
 
  -- 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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