ax_c_compile_value
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Synopsis
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     AX_C_COMPILE_VALUE (COMPILE-VALUE, ALIAS, INCLUDES)

Description
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The AX_C_COMPILE_VALUE macro determines a compile time value by generating the object code and reading the value from the code. Static data initializers like sizeof(int) are unavailable to preprocessor. The macro calculates the values known to compiler's static initializer.

Assumptions: The sought value should not exceed 65535. The shell interpreter and the sed utility are expected to exist and work similarly across possible build platforms.

Result: The resulting configure script will generate the preprocessor symbol definition:

       #define COMPILE_VALUE_<ALIAS> <NUMBER>

It was important that the value was embedded into the object file in a predefined byte order during the test. This ensured that the result was independent from the target platform's byte order.

The existing AC_CHECK_SIZEOF macro also computes the size of the given type without running the test program. However, the existing macro will produce a piece of configure script that will take the time proportional to the logarithm of the sought value.

Example of use in configure.in:

       AX_C_COMPILE_VALUE(sizeof(int), sizeof_int)
       AX_C_COMPILE_VALUE([sizeof(int[[543]])], sizeof_int543)

As a result of runnfing the generated configure script, the following definition will appear in config.h:

       #define COMPILE_VALUE_SIZEOF_INT 4
       #define COMPILE_VALUE_SIZEOF_INT543 2172

Source Code
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Download the latest version of ax_c_compile_value.m4 (http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_c_compile_value.m4) or browse the macro's revision history (http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_c_compile_value.m4).

License
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Copyright © 2008 Ilguiz Latypov

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 2 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 <http://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 scripts that are the output of Autoconf when processing the Macro. You need not follow the terms of the GNU General Public License when using or distributing such scripts, even though portions of the text of the Macro appear in them. The GNU General Public License (GPL) does govern all other use of the material that constitutes the Autoconf Macro.

This special exception to the GPL applies to versions of the Autoconf Macro released by the Autoconf Archive. When you make and distribute a modified version of the Autoconf Macro, you may extend this special exception to the GPL to apply to your modified version as well.