using_ccache.md

CCache

CCache is a fantastic tool for speeding up compile and recompilation times.

It is best supported on Linux and MacOS using either GCC or Clang, but has good support for several other platforms and compilers as well. For instance, I used it to compile wxWidgets on Windows using MinGW-w64 GCC without issue.

Using CCache in a CMake Build

The best way to use CCache in a CMake build is to use it as a compiler launcher by setting the CMAKE_C_COMPILER_LAUNCHER and CMAKE_CXX_COMPILER_LAUNCHER environment variables to use ccache.

Initial Project Configure

First, set the environment variables for the current shell session.

Windows (PowerShell):

# PowerShell
$env:CMAKE_C_COMPILER_LAUNCHER='ccache'
$env:CMAKE_CXX_COMPILER_LAUNCHER='ccache'

Linux/MacOS (bash):

CMAKE_C_COMPILER_LAUNCHER='ccache'
CMAKE_CXX_COMPILER_LAUNCHER='ccache'

Then run the initial CMake configuration. Upon first configuration, CMake will read the values of CMAKE_C_COMPILER_LAUNCHER and CMAKE_CPP_COMPILER_LAUNCHER and use those to launch the respective C and C++ compilers.

# Example
cmake -B build/ -DCMAKE_BUILD_TYPE=Release

Then build the project as usual.

Subsequent Project Configure

If running a subsequent CMake configuration in a project where ccache wasn't used as the compiler launcher, you'll need to set the CMake cache variables directly instead:

cmake -B build/ -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_COMPILER_LAUNCHER=ccache -DCMAKE_CXX_COMPILER_LAUNCHER=ccache

Then build the project as usual.