The config.m4 File (Programming PHP)

14.4.1. No External Dependencies

Here is a sample from the simple EXIF extension, which has no external dependencies:

dnl config.m4 for extension exif
  
PHP_ARG_ENABLE(exif, whether to enable exif support,
 [  --enable-exif           Enable exif support])
  
if test "$PHP_EXIF" != "no"; then
  AC_DEFINE(HAVE_EXIF, 1, [Whether you want exif support])
  PHP_EXTENSION(exif, $ext_shared)
fi

The dnl string indicates a comment line. Here we define HAVE_EXIF if --enable-exif was given. In our exif.c code, we then surround the whole file with:

#if HAVE_EXIF
...
#endif

This ensures that no EXIF functionality is compiled in unless the feature was requested. The PHP_EXTENSION line enables this extension to be compiled as a shared, dynamically loadable extension using --enable-exif=shared.

14.4.2. External Dependencies

The libswf extension (which builds Flash animations) requires the libswf library. To enable it, configure PHP with --with-swf. The config.m4 file for libswf must find the library if it wasn't supplied via --with-swf=/path/to/lib: for the libswf extension.

dnl config.m4 for extension libswf
  
PHP_ARG_WITH(swf, for libswf support,
[  --with-swf[=DIR]        Include swf support])
  
if test "$PHP_SWF" != "no"; then
  if test -r $PHP_SWF/lib/libswf.a; then
    SWF_DIR=$PHP_SWF
  else
    AC_MSG_CHECKING(for libswf in default path)
    for i in /usr/local /usr; do
      if test -r $i/lib/libswf.a; then
        SWF_DIR=$i
        AC_MSG_RESULT(found in $i)
      fi
    done
  fi
  
  if test -z "$SWF_DIR"; then
    AC_MSG_RESULT(not found)
    AC_MSG_ERROR(Please reinstall the libswf distribution - swf.h should 
                 be <swf-dir>/include and libswf.a should be in <swf-dir>/lib)
  fi
  PHP_ADD_INCLUDE($SWF_DIR/include)
  
  PHP_SUBST(SWF_SHARED_LIBADD)
  PHP_ADD_LIBRARY_WITH_PATH(swf, $SWF_DIR/lib, SWF_SHARED_LIBADD)
  AC_DEFINE(HAVE_SWF,1,[ ])
  
  PHP_EXTENSION(swf, $ext_shared)
fi

The AC_MSG_CHECKING( ) macro is used to make configure print a message about what it's checking for. When we've found the include files, we add them to PHP's standard include search path with the PHP_ADD_INCLUDE( ) macro. When we find the SWF shared libraries, we add them to the library search path and ensure that we link them into the final binary through the PHP_ADD_LIBRARY_WITH_PATH( ) macro. Things can get a lot more complex than this once you start worrying about different versions of libraries and different platforms. For a very complex example, see the GD library's config.m4 in ext/gd/config.m4.

14.4. The config.m4 File

14.4.1. No External Dependencies

14.4.2. External Dependencies