Is it possible to rename cmake's build directory? - cmake

Question

cmake uses ./build as a standard place to generate build system and to place all intermediate files. Is this a hard requirement or is it possible to use a different name such as ./work? or maybe ./work/build?
To put in context this question. This is an initial idea so I can keep the same top level workflow for different project languages and toolchains.

Answer 1

Yes. The notion that CMake has a "standard" binary directory is incorrect. There is no default. Using build is common, but it is truly just a convention. In general, you can run:
$ cmake -G Ninja -S /path/to/source-dir -B /path/to/binary-dir -DCMAKE_BUILD_TYPE=RelWithDebInfo [...more options...]
Where /path/to/source-dir is the path to the folder containing the top-level CMakeLists.txt. People commonly run CMake from this folder, so this is often just -S .. Similarly, the binary directory, /path/to/binary-dir, is commonly stored beneath the source directory in a folder called build. So in these cases you will see -B ./build.
The values of both flags may be arbitrary, however.
For instance, when building LLVM, I often write:
$ cmake ... -S llvm -B build ...
because LLVM's "top-level" CMakeLists.txt is actually in the llvm/ subfolder of their monorepo structure. But I still keep the build directory at the top level. I could just as easily have written:
$ cmake ... -S llvm -B $HOME/.binary-trees/llvm ...
Which is a little odd, but perfectly valid.

Answer 2

cmake uses ./build as a standard place to generate build system [...]
This is incorrect. If you're using cmake for configuring without providing a preset and without specifying the source/build directory using the -S ... -B ... options, the current working directory is used as build directory.
A convenient way of providing multiple configurations that also benefits from integration with some IDEs are cmake presets.
Put something like the following in a CMakePresets.json file next to your toplevel CMakeLists.txt file.
{
"version": 3,
"cmakeMinimumRequired": {
"major": 3,
"minor": 21,
"patch": 0
},
"configurePresets": [
{
"name": "linux-x86",
"displayName": "linux-x86",
"description": "Linux build release build targeting the x86 architecture",
"generator": "Unix Makefiles",
"toolchainFile": "${sourceDir}/toolchains/linux-x86.cmake"
"binaryDir": "${sourceDir}/build/linux-x86",
"cacheVariables": {
"CMAKE_BUILD_TYPE": {
"type": "STRING",
"value": "Release"
}
}
},
{
"name": "linux-x86-debug",
"displayName": "linux-x86-debug",
"description": "Linux build debug build targeting the x86 architecture",
"inherits": "linux-x86",
"binaryDir": "${sourceDir}/build/linux-x86-debug",
"cacheVariables": {
"CMAKE_BUILD_TYPE": {
"type": "STRING",
"value": "Debug"
}
}
},
{
"name": "linux-aarch64",
"displayName": "linux-aarch64",
"description": "Linux build release build targeting the aarch64 architecture",
"inherits": "linux-x86",
"binaryDir": "${sourceDir}/build/linux-aarch64",
"toolchainFile": "${sourceDir}/toolchains/linux-aarch64.cmake"
},
{
"name": "linux-aarch64-debug",
"displayName": "linux-aarch64-debug",
"description": "Linux build debug build targeting the aarch64 architecture",
"inherits": "linux-x86-debug",
"binaryDir": "${sourceDir}/build/linux-aarch64-debug",
"toolchainFile": "${sourceDir}/toolchains/linux-aarch64.cmake"
}
, ...
]
}
This does require a minimum cmake version of 3.19 though, 3.21 for this specific json file.
This allows you to use commands like
cmake --preset linux-aarch64-debug .
cmake --preset linux-x86 .
To set up the aarch64 debug build and the linux-x86 release build in build/linux-aarch64-debug and build/linux-x86 respectively.