[cfe-dev] Doc suggestion: include info on -include-pch option

[Casey Rodarmor]

Hi all,

I started to use precompiled headers with Clang the other day, and I was a
little confused with the documentation at
http://clang.llvm.org/docs/UsersManual.html#generating-a-pch-file

To make a long story short, I found the combination of generating a PCH
file and then using "-include my_pch_header.h" to get clang to use it
pretty hard to get right. I messed it up a few times, including putting the
PCH in the wrong directory, and accidentally generating a bad PCH file, but
I didn't get any helpful messages pointing me toward what was wrong.

Eventually I found the flag "-include-pch", which when enabled immediately
started to give my helpful errors and warnings, like the fact that clang
couldn't find my PCH file, or that when it did it wasn't even a pch file,
and I soon got everything working.

My suggestion is to replace the example "clang -include test.h test.c -o
test" in the user manual with "clang -include-pch test.h.gch test.c -o
test", since it seems less error prone.

Best regards,
Casey
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