(autoconf.info.gz) Examining Declarations

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 Examining Declarations
 ======================
 
    The macro `AC_TRY_CPP' is used to check whether particular header
 files exist.  You can check for one at a time, or more than one if you
 need several header files to all exist for some purpose.
 
  - Macro: AC_TRY_CPP (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
      If the preprocessor produces no error messages while processing the
      INPUT (typically includes), run shell commands ACTION-IF-TRUE.
      Otherwise run shell commands ACTION-IF-FALSE.  Beware that INPUT
      is double quoted.  Shell variable, back quote, and backslash
      substitutions are performed on INPUT.
 
      This macro uses `CPPFLAGS', but not `CFLAGS', because `-g', `-O',
      etc. are not valid options to many C preprocessors.
 
    Here is how to find out whether a header file contains a particular
 declaration, such as a typedef, a structure, a structure member, or a
 function.  Use `AC_EGREP_HEADER' instead of running `grep' directly on
 the header file; on some systems the symbol might be defined in another
 header file that the file you are checking `#include's.
 
  - Macro: AC_EGREP_HEADER (PATTERN, HEADER-FILE, ACTION-IF-FOUND,
           [ACTION-IF-NOT-FOUND])
      If the output of running the preprocessor on the system header file
      HEADER-FILE matches the extended regular expression PATTERN,
      execute shell commands ACTION-IF-FOUND, otherwise execute
      ACTION-IF-NOT-FOUND.
 
    To check for C preprocessor symbols, either defined by header files
 or predefined by the C preprocessor, use `AC_EGREP_CPP'.  Here is an
 example of the latter:
 
      AC_EGREP_CPP(yes,
      [#ifdef _AIX
        yes
      #endif
      ], is_aix=yes, is_aix=no)
 
  - Macro: AC_EGREP_CPP (PATTERN, PROGRAM, [ACTION-IF-FOUND],
           [ACTION-IF-NOT-FOUND])
      PROGRAM is the text of a C or C++ program, on which shell
      variable, back quote, and backslash substitutions are performed.
      If the output of running the preprocessor on PROGRAM matches the
      extended regular expression PATTERN, execute shell commands
      ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.
 
      This macro calls `AC_PROG_CPP' or `AC_PROG_CXXCPP' (depending on
      which language is current,  Language Choice), if it hasn't
      been called already.
 

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