(autoconf.info)Generic Types

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5.9.2 Generic Type Checks

These macros are used to check for types not covered by the "particular"
test macros.

     Check whether TYPE is defined.  It may be a compiler builtin type
     or defined by the INCLUDES.  INCLUDES is a series of include
     directives, defaulting to `AC_INCLUDES_DEFAULT' (Note: Default
     Includes), which are used prior to the type under test.

     In C, TYPE must be a type-name, so that the expression `sizeof
     (TYPE)' is valid (but `sizeof ((TYPE))' is not).  The same test is
     applied when compiling for C++, which means that in C++ TYPE
     should be a type-id and should not be an anonymous `struct' or

     For each TYPE of the TYPES that is defined, define `HAVE_TYPE' (in
     all capitals).  Each TYPE must follow the rules of
     `AC_CHECK_TYPE'.  If no INCLUDES are specified, the default
     includes are used (Note: Default Includes).  If ACTION-IF-FOUND
     is given, it is additional shell code to execute when one of the
     types is found.  If ACTION-IF-NOT-FOUND is given, it is executed
     when one of the types is not found.

     This macro uses M4 lists:
          AC_CHECK_TYPES([unsigned long long int, uintmax_t])
          AC_CHECK_TYPES([float_t], [], [], [[#include <math.h>]])

   Autoconf, up to 2.13, used to provide to another version of
`AC_CHECK_TYPE', broken by design.  In order to keep backward
compatibility, a simple heuristic, quite safe but not totally, is
implemented.  In case of doubt, read the documentation of the former
`AC_CHECK_TYPE', see Note: Obsolete Macros.

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