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Is it possible to extract original filename (filepath) and compilation language from precompiled header? As I understand it's possible for Clang using llvm-bcanalyzer (LLVM bit code analyzer). So, could anybody help me with GCC?

vromanik
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  • A precompiled header most likely combines a lot (transcluded) .h files. What name exactly to do seek? – Kijewski Dec 08 '16 at 14:04
  • I tried to found the original header name which is the source for precompiled header. According to documentation you can create PHC using the follow command: gcc -x c-header **test.h** -o test.h.gch. In my case I would like to extract the path to **test.h** – vromanik Dec 08 '16 at 14:14
  • Yes. Clang allows me to receive that information [Clang PHC Internal metadata] (http://clang.llvm.org/docs/PCHInternals.html#ast-file-contents). – vromanik Dec 08 '16 at 14:21

1 Answers1

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For clang you can easily extract original PCH filename just parsing preprocessor output. In out example header/header.h is original header and pch/pch.h.gch is precompiled header.

For example the follow command: clang -E -include pch/pch.h main.cpp returns result where we can find original PCH filename: 

…
# 1 "/Users/user/pch_example/header/header.h" 1
…
# 1 "main.cpp" 2
int main() {return 42;}

Unfortunately parsing preprocessor output doesn’t help us with GCC, even if you use it with -fpch-preprocess option. So the only one way I found is compiling PCH with enabled dependency-tracking flag like -MD (or -MMD).

For example we can call the follow command: gcc-6 -MMD -x c++-header header/header.h -o pch/pch.h.pch. In this case GCC additionally generates dependency-file pch/pch.h.d, which contains path to the original PCH filename.

vromanik
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