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AC_COMPILE_CHECK_SIZEOF(TYPE [, HEADERS [, EXTRA_SIZES...]])
This macro checks for the size of TYPE using compile checks, not run checks. You can supply extra HEADERS to look into. the check will cycle through 1 2 4 8 16 and any EXTRA_SIZES the user supplies. If a match is found, it will #define SIZEOF_`TYPE' to that value. Otherwise it will emit a configure time error indicating the size of the type could not be determined.
The trick is that C will not allow duplicate case labels. While this is valid C code:
switch (0) case 0: case 1:;
The following is not:
switch (0) case 0: case 0:;
Thus, the AC_TRY_COMPILE will fail if the currently tried size does not match.
Here is an example skeleton configure.in script, demonstrating the macro's usage:
AC_PROG_CC AC_CHECK_HEADERS(stddef.h unistd.h) AC_TYPE_SIZE_T AC_CHECK_TYPE(ssize_t, int) headers='#ifdef HAVE_STDDEF_H #include <stddef.h> #endif #ifdef HAVE_UNISTD_H #include <unistd.h> #endif ' AC_COMPILE_CHECK_SIZEOF(char) AC_COMPILE_CHECK_SIZEOF(short) AC_COMPILE_CHECK_SIZEOF(int) AC_COMPILE_CHECK_SIZEOF(long) AC_COMPILE_CHECK_SIZEOF(unsigned char *) AC_COMPILE_CHECK_SIZEOF(void *) AC_COMPILE_CHECK_SIZEOF(size_t, $headers) AC_COMPILE_CHECK_SIZEOF(ssize_t, $headers) AC_COMPILE_CHECK_SIZEOF(ptrdiff_t, $headers) AC_COMPILE_CHECK_SIZEOF(off_t, $headers)
Kaveh Ghazi <ghazi@caip.rutgers.edu>
2000-07-19
AC_DEFUN([AC_COMPILE_CHECK_SIZEOF], [changequote(<<, >>)dnl dnl The name to #define. define(<<AC_TYPE_NAME>>, translit(sizeof_$1, [a-z *], [A-Z_P]))dnl dnl The cache variable name. define(<<AC_CV_NAME>>, translit(ac_cv_sizeof_$1, [ *], [_p]))dnl changequote([, ])dnl AC_MSG_CHECKING(size of $1) AC_CACHE_VAL(AC_CV_NAME, [for ac_size in 4 8 1 2 16 $2 ; do # List sizes in rough order of prevalence. AC_TRY_COMPILE([#include "confdefs.h" #include <sys/types.h> $2 ], [switch (0) case 0: case (sizeof ($1) == $ac_size):;], AC_CV_NAME=$ac_size) if test x$AC_CV_NAME != x ; then break; fi done ]) if test x$AC_CV_NAME = x ; then AC_MSG_ERROR([cannot determine a size for $1]) fi AC_MSG_RESULT($AC_CV_NAME) AC_DEFINE_UNQUOTED(AC_TYPE_NAME, $AC_CV_NAME, [The number of bytes in type $1]) undefine([AC_TYPE_NAME])dnl undefine([AC_CV_NAME])dnl ])