Sharing precompiled headers between projects in Visual Studio

While this is an old question I want to give a new answer which works in Visual Studio 2017 and does not involve any copying. Only disadvantage: Edit and continue doesn't work anymore.

Basically you have to create a new project for the precompiled header and have all other project depend on it. Here is what I did:

Step by step:

1. Create a new project withnin your solution which includes the header (called pch.h from hereon) and a one line cpp file which includes pch.h. The project should create a static lib. Setup the new project to create a precompiled header. The output file needs to be accessible by all projects. for me this relative to IntDir, but for default settings it could be relative to $(SolutionDir). The pch project must only have defines all others projects have too.

   

2. Have all other projects depend on this new project. Otherwise the build order might be wrong.

   

3. Setup all other projects to use the pch.h. See, how the output file parameters are the same as in the pch project. Additional include directories also need to point to the pch.h directory. Optionally you can force include the pch file in every cpp (or you include it manually in the first line of every cpp file).

   

   4. Setup all projects (including the pch project) to use the same compiler symbol file (the linker symbol file is not affected). Again, in my example this is OutDir but in your solution this might vary. It has to point to the same file on disk. The Debug Information Format needs to be set to C7 (see screenshot above), otherwise Visual Studio will not be able to compile projects in parallel.

I hope I didn't forget anything. For my solution (130k loc, 160 projects) this lead to a compile time of ~2:30mins instead of ~3:30mins.

Yes it is possible and I can assure you, the time savings are significant. When you compile your PCH, you have to copy the .pdb and .idb files from the project that is creating the PCH file. In my case, I have a simple two file project that is creating a PCH file. The header will be your PCH header and the source will be told to create the PCH under project settings - this is similar to what you would do normally in any project. As you mentioned, you have to have the same compile settings for each configuration otherwise a discrepancy will arise and the compiler will complain.

Copying the above mentioned files every time there is a rebuild or every time the PCH is recompiled is going to be a pain, so we will automate it. To automate copying, perform a pre-build event where the above mentioned files are copied over to the appropriate directory. For example, if you are compiling Debug and Release builds of your PCH, copy the files from Debug of your PCH project over to your dependent project's Debug. So a copy command would look like this

copy PchPath\Debug*.pdb Debug\ /-Y

Note the /-Y at the end. After the first build, each subsequent build is incrementally compiled, therefore if you replace the files again, Visual Studio will complain about corrupted symbols. If they do get corrupted, you can always perform a rebuild, which will copy the files again (this time it won't skip them as they no longer exist - the cleanup deletes the files).

I hope this helps. It took me quite some time to be able to do this, but it was worth it. I have several projects that depend on one big framework, and the PCH needs to be compiled only once. All the dependent projects now compile very quickly.

EDIT: Along with several other people, I have tested this under VS2010 and VS2012 and it does appear to work properly.