CPM.cmake/README.md

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# CPM

CPM is a simple dependency manager written in CMake. It downloads and adds packages via `FetchContent` or uses locally installed packages via `find_package`.

# Supported packages

Any project that you can add via `add_subdirectory` should already work with CPM.

# Usage

To add a new dependency to your project simply add the Projects target name, the git URL and the version. If the git tag for this version does not match the pattern `v$VERSION`, then the exact branch or tag can be specified with the `GIT_TAG` argument. CMake options can also be supplied with the package.

```cmake
cmake_minimum_required(VERSION 3.14 FATAL_ERROR)

# create project
project(MyProject)

# add dependencies
include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/CPM.cmake)

CPMAddPackage(
  NAME LarsParser
  VERSION 1.8
  GIT_REPOSITORY https://github.com/TheLartians/Parser.git
  GIT_TAG v1.8 # optional here, as indirectly defined by VERSION
  OPTIONS      # optional CMake arguments passed to the dependency
    "LARS_PARSER_BUILD_GLUE_EXTENSION ON"
)

# add executable
set (CMAKE_CXX_STANDARD 17)
add_executable(my-project my-project.cpp)
target_link_libraries(my-project LarsParser)
```

See the [examples directory](https://github.com/TheLartians/CPM/tree/master/examples) for more examples.

# Adding CPM

To add CPM to your current project, simply include add `cmake/CPM.cmake` to your projects `cmake` directory. The command below will perform this automatically.

```bash
wget -O cmake/CPM.cmake https://raw.githubusercontent.com/TheLartians/CPM/master/cmake/CPM.cmake
```

# Options

If you set the CMake option `CPM_REMOTE_PACKAGES_ONLY` to `On`, packages will always be fetched via the URL. Setting `CPM_LOCAL_PACKAGES_ONLY` to `On` will only add packages via `find_package`.

# Advantages

- **Small repos** CPM takes care of package dependencies, allowing programmers to focus on creating small well-tested frameworks.
- **Cross-Plattform** CPM adds projects via `add_subdirectory`, which is compatible with all cmake toolchains and generators. 
- **Reproducable builds** By using versioning via git tags it is ensured that a project will always be in the same state everywhere.
- **No installation required** No need to install anything. Just add the script to your project and you're good to go.

# Limitations

- **First version used** In diamond-shaped dependency graphs (e.g. `A` depends on `C`(v1.1) and `A` depends on `B` depends on `C`(v1.2)) the first added dependency will be used (in this case `C`@1.1). If the current version is older than the version beeing added, or if provided options are incompatible, a CMake warning will be emitted.
- **No auto-update** To update a dependency, version numbers or git tags in the cmake scripts must be adapted manually.