Sharing precompiled headers between projects in Visual Studio

Assaf_11208 0
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I have a solution with many Visual C++ projects, all using PCH, but some have particular compiler switches turned on for project-specific needs.

Most of these projects share the same set of headers in their respective stdafx.h (STL, boost, etc). I'm wondering if it's possible to share PCH between projects, so that instead of compiling every PCH per-project I could maybe have one common PCH that most projects in the solution could just use.

It seems possible to specify the location of the PCH as a shared location in the project settings, so I have a hunch this could work. I'm also assuming that all source files in all projects that use a shared PCH would have to have the same compiler settings, or else the compiler would complain about inconsistencies between the PCH and the source file being compiled.

Has anyone tried this? Does it work?

A related question: should such a shard PCH be overly inclusive, or would that hurt overall build time? For example, a shared PCH could include many STL headers that are widely used, but some projecst might only need <string> and <vector>. Would the time saved by using a shared PCH have to be paid back at a later point in the build process when the optimizer would have to discard all the unused stuff dragged into the project by the PCH?

pch precompiled-headers visual-c++ c++
6 Answers

It seems it's not possible because each source file has to be compiled against the same PDB against which the PCH was compiled. darn it.

Assaf_112080

Samaursa's answer worked for me.

I also saw this link that works (look for Reginald's answer near the bottom).

This one uses copy while Reginald's uses xcopy (I prefer xcopy). Either way, thanks--this sped up my builds considerably.

user_5451310

This sounds like a case of "diminishing returns" to me. Suppose including the common headers directly wastes 1 second per .cpp file, and each target (DLL/EXE) has 10 .cpp files. By using a .pch per target, you save 10 seconds per target. If your whole project has 10 targets, you save 1.5 minutes on the whole build, which is good.

But by reducing it to one .pch for the whole project, you'd only save a further 9 seconds. Is it worth it? The extra effort (which may be a lot more fiddly to set up, being a non-standard configuration unsupported by VS wizards) produces only a 10th of the saving.

Earwicker_274230

On 2012, you can use a PDB and just build the pch from a lib project that only builds the pch and the main project that depends on the pch lib into the same directory (no copying), unfortunately this doesn't work with 2013+ except via a long winded work-a-round.

user_7761150
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