C and C++ compilers aren’t the fastest pieces of software out there and there’s no lack of programmer jokes based on tedium of waiting for their work to complete.

There are ways to fix the pain though - one of them is ccache. CCache improves compilation times by caching previously built object files in private cache and reusing them when you’re recompiling same objects with same parameters. Obviously it will not help if you’re compiling the code for the first time and it also won’t help if you often change compilation flags. Most C/C++ development however involves recompiling same object files with the same parameters and ccache helps alot.

For illustration, here’s the comparison of first and subsequent compilation times of a largish C++ project:

Original run with empty cache:

make -j9
...
real    0m56.684s
user    5m31.996s
sys     0m41.638s

Recompilation with warm cache:

make -j9
...
real    0m5.929s
user    0m11.896s
sys     0m8.722s

### Installation

CCache is available in repositories on pretty much all distributions. On OS X use homebrew:

brew install ccache

and on Debian-based distros use apt:

apt-get install ccache

### CMake configuration

After ccache is installed, you need to tell CMake to use it as a wrapper for the compiler. Add these lines to your CMakeLists.txt:

# Configure CCache if available
find_program(CCACHE_FOUND ccache)
if(CCACHE_FOUND)
set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
endif(CCACHE_FOUND)

Rerun cmake and next make should use ccache for wrapper.

### Usage with Android NDK

CCache can even be used on Android NDK - you just need to export NDK_CCACHE environment variable with path to ccache binary. ndk-build script will automatically use it. E.g.

export NDK_CCACHE=/usr/local/bin/ccache
ndk-build -j9

(Note that on Debian/Ubuntu the path will probably be /usr/bin/ccache)

### CCache statistics

To see if ccache is really working, you can use ccache -s command, which will display ccache statistics:

cache directory                     /Users/jernej/.ccache
primary config                      /Users/jernej/.ccache/ccache.conf
max cache size                      20.0 GB