CODEWITHSUNDEEP
c++compilation
Tarek
Tarek

Reputation: 1090

How to avoid recompiling header files

My single C++ file includes many header files from various libraries such as MKL and template libraries. Compiling this single file every time takes a long time due to the many include statements. I tried separating the include statements in a single file, making an object file out of it, and linking it during the compilation of the main file, but it seems the compiler doesn't recognize the definitions of the objects and functions that are defined in the header files. So, how can I save the compilation time of these header files?

Upvotes: 1

Views: 653

Answers (1)

Spacemoose
Spacemoose

Reputation: 4016

Precompiled headers:

What you are doing does sound like it would benefit heavily from precompiled headers (pch's). The intel compiler does support pch's, as you can see here:

https://software.intel.com/en-us/node/522754.

Installing tools without root permissions

You can still experiment with ccache to see if that will help your situation -- it can make a huge difference in cases where units do not need to be recompiled, which happens surprisingly often. The path to doing this is to install ccache locally. Generally this can be done by downloading sources to a directory where you have write access (I keep an install folder in my home directory) , and then following the build directions for that project. Once the executable are built, you'll have to add the path for the executable to your path -- by doing

export PATH=$PATH:the-path-to-your-compiled-executables.

in BASH. At that point ccache will be available to your user.

A better explanation is available here: https://unix.stackexchange.com/questions/42567/how-to-install-program-locally-without-sudo-privileges

CMAKE, cotire, etc

One final point -- I haven't read the docu for the intel compiler's pch support, but pch support generally involves some manual code manipulation to instruct the compile which header to precompile and so on. I recommend looking in to managing your build with CMAKE, and using the cotire plugin to experiment with pch.

While I have gripes about CMAKE from a software engineering perspective, it does make managing your build, and especially experimenting with various ways to speed up your build, much much easier. After experimenting with pch's, and ccache, you could also try out ninja instead of make and see if that gets you any improvement.

Good luck.

Upvotes: 5

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