What is the difference between “Create Precompiled Header” (/Yc) and “Use Precompiled Header” (/Yu) in Visual Studio?

StackOverflow https://stackoverflow.com/questions/11722944

Question

I read the documentation in MSDN, but in the end I didn't get a clear idea what is the practical difference between them, exactly. Both seem to require stdafx.h to be added at the top of every *.cpp file.

I'm using VS2008.

Can anyone help clear things up?

Was it helpful?

Solution

Well, I think that you must first understand the purpose of precompiled headers. In large projects, it can take ages to process all the headers required by a single client extension for example, so some people prefer to distribute the .pch files along with their libraries. In order to generate the .pch files, you use the /Yc compiler flag and the person who wants to consume your library will set the /Yu flag. See here and here for details.

OTHER TIPS

Short summary of how to use PCH files in Visual Studio:

  • All cpp files in the project have to include stdafx.h (you can change this to something else if you wish)
  • Select project in Solution Explorer and in Properties -> C++ -> Precompiled Headers set 'Create/Use precompiled headers' to 'Use'. Hit Apply
  • While the Property Pages are still shown select stdafx.cpp in solution explorer and set the value to 'Create'
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