This option instructs the compiler to use a PCH file if it
exists, and to create a PCH file otherwise.
When the option --pch is specified, the compiler
searches for a PCH file with the name filename.pch,
where filename.* is
the name of the primary source file. The compiler uses the PCH file filename.pch if
it exists, and creates a PCH file named filename.pch in
the same directory as the primary source file otherwise.
Restrictions
This option has no effect if you include either the option --use_pch=filename or
the option --create_pch=filename on
the same command line.