B.2.124.4 Directing the Compiler to Use a Specific Precompiled-Header File

You can also direct the compiler to use a specific precompiled header. Specify -xpch=use:pch_filename to do this. You can specify any number of source files with the same sequence of include files as the source file that was used to create the precompiled-header file. For example, your command in use mode could look like this: cc -xpch=use:foo.cpch foo.c bar.c foobar.c.

You should only use an existing precompiled-header file if the following are true. If any of the following is not true, you should recreate the precompiled-header file:

• The compiler that you are using to access the precompiled-header file is the same as the compiler that created the precompiled-header file. A precompiled-header file created by one version of the compiler may not be usable by another version of the compiler.

• Except for the -xpch option, the compiler options you specify with -xpch=use must match the options that were specified when the precompiled-header file was created.

• The set of included headers you specify with -xpch=use is identical to the set of headers that were specified when the precompile header was created.

• The contents of the included headers that you specify with -xpch=use is identical to the contents of the included headers that were specified when the precompiled header was created.

• The current directory (that is, the directory in which the compilation is occurring and attempting to use a given precompiled-header file) is the same as the directory in which the precompiled-header file was created.

• The initial sequence of pre-processing directives, including #include directives, in the file you specified with -xpch=collect are the same as the sequence of pre-processing directives in the files you specify with -xpch=use.