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.
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.