path: root/src/development/cmake.md

# cmake(1)

## Frequently used variables
```
# Install location.
CMAKE_INSTALL_PREFIX=<path>

# Generate compile_commands.json?
CMAKE_EXPORT_COMPILE_COMMANDS={0,1}

# Project build type.
CMAKE_BUILD_TYPE={Debug, Release, RelWithDebInfo, MinSizeRel}

# C++ standard.
CMAKE_CXX_STANDARD={14,17,..}
```

## `PRIVATE` / `PUBLIC` / `INTERFACE`

These modifier control where properties for a given target are visible.

- `PRIVATE`: Only for the target itself.
- `INTERFACE`: Only for anyone linking against the target.
- `PUBLIC`: For the target itself and anyone linking against it (effectively
  `PRIVATE` + `INTERFACE`).

The following gives an example for preprocessor definitions specified on a
library target. This behaves in the same way for other properties like for
example include directories.
```cmake
# CMakeLists.txt

cmake_minimum_required(VERSION 3.14)
project(moose)

# -- LIBRARY
add_library(liba STATIC liba.cc)
target_compile_definitions(liba PUBLIC DEF_PUBLIC)
target_compile_definitions(liba PRIVATE DEF_PRIVATE)
target_compile_definitions(liba INTERFACE DEF_INTERFACE)

# -- APPLICATION
add_executable(main main.cc)
target_link_libraries(main liba)
```

```sh
> touch liba.cc; echo "int main() {}" > main.cc
> cmake -B build -S . -G Ninja
> ninja -C build -j1 --verbose
[1/4] /usr/bin/c++ -DDEF_PRIVATE -DDEF_PUBLIC  [..] .../liba.cc
[2/4] [..]
[3/4] /usr/bin/c++ -DDEF_INTERFACE -DDEF_PUBLIC [..] .../main.cc
[4/4] [..]
```

## `find_package` [[ref][cmake-find_package]]
A small example to play with can be found in [cmake/module][src-module].

```cmake
find_package(Name MODULE)
```
Looks for `FindName.cmake` in paths given by `CMAKE_MODULE_PATH` and then builtin paths.

```cmake
find_package(Name CONFIG)
```
Looks for `name-config.cmake` or `NameConfig.cmake` in paths given by
`CMAKE_PREFIX_PATH`, or path given by `Name_DIR` and then builtin paths.

[cmake-include]: https://cmake.org/cmake/help/latest/command/include.html
[cmake-find_package]: https://cmake.org/cmake/help/latest/command/find_package.html
[src-module]: https://github.com/johannst/notes/tree/master/src/development/cmake/module