@node ax_compile_check_sizeof
@unnumberedsec ax_compile_check_sizeof

@majorheading Synopsis

@smallexample
AX_COMPILE_CHECK_SIZEOF(TYPE [, HEADERS [, EXTRA_SIZES...]])
@end smallexample

@majorheading Description

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:

@smallexample
  switch (0) case 0: case 1:;
@end smallexample

The following is not:

@smallexample
  switch (0) case 0: case 0:;
@end smallexample

Thus, the AC_COMPILE_IFELSE will fail if the currently tried size does
not match.

Here is an example skeleton configure.in script, demonstrating the
macro's usage:

@smallexample
  AC_PROG_CC
  AC_CHECK_HEADERS(stddef.h unistd.h)
  AC_TYPE_SIZE_T
  AC_CHECK_TYPE(ssize_t, int)
@end smallexample

@smallexample
  headers='#ifdef HAVE_STDDEF_H
  #include <stddef.h>
  #endif
  #ifdef HAVE_UNISTD_H
  #include <unistd.h>
  #endif
  '
@end smallexample

@smallexample
  AX_COMPILE_CHECK_SIZEOF(char)
  AX_COMPILE_CHECK_SIZEOF(short)
  AX_COMPILE_CHECK_SIZEOF(int)
  AX_COMPILE_CHECK_SIZEOF(long)
  AX_COMPILE_CHECK_SIZEOF(unsigned char *)
  AX_COMPILE_CHECK_SIZEOF(void *)
  AX_COMPILE_CHECK_SIZEOF(size_t, $headers)
  AX_COMPILE_CHECK_SIZEOF(ssize_t, $headers)
  AX_COMPILE_CHECK_SIZEOF(ptrdiff_t, $headers)
  AX_COMPILE_CHECK_SIZEOF(off_t, $headers)
@end smallexample

@majorheading Source Code

Download the
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_compile_check_sizeof.m4,latest
version of @file{ax_compile_check_sizeof.m4}} or browse
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_compile_check_sizeof.m4,the
macro's revision history}.

@majorheading License

@w{Copyright @copyright{} 2008 Kaveh Ghazi @email{ghazi@@caip.rutgers.edu}} @* @w{Copyright @copyright{} 2017 Reini Urban @email{rurban@@cpan.org}}

This program is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details.

You should have received a copy of the GNU General Public License along
with this program. If not, see <https://www.gnu.org/licenses/>.

As a special exception, the respective Autoconf Macro's copyright owner
gives unlimited permission to copy, distribute and modify the configure
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