104 lines
3.3 KiB
Markdown
104 lines
3.3 KiB
Markdown
|
# CMake
|
||
|
|
|
||
|
|
You can also use the `nlohmann_json::nlohmann_json` interface target in CMake. This target populates the appropriate usage requirements for `INTERFACE_INCLUDE_DIRECTORIES` to point to the appropriate include directories and `INTERFACE_COMPILE_FEATURES` for the necessary C++11 flags.
|
||
|
|
|
||
|
|
## External
|
||
|
|
|
||
|
|
To use this library from a CMake project, you can locate it directly with `find_package()` and use the namespaced imported target from the generated package configuration:
|
||
|
|
|
||
|
|
```cmake
|
||
|
|
# CMakeLists.txt
|
||
|
|
find_package(nlohmann_json 3.2.0 REQUIRED)
|
||
|
|
...
|
||
|
|
add_library(foo ...)
|
||
|
|
...
|
||
|
|
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
|
||
|
|
```
|
||
|
|
|
||
|
|
The package configuration file, `nlohmann_jsonConfig.cmake`, can be used either from an install tree or directly out of the build tree.
|
||
|
|
|
||
|
|
## Embedded
|
||
|
|
|
||
|
|
To embed the library directly into an existing CMake project, place the entire source tree in a subdirectory and call `add_subdirectory()` in your `CMakeLists.txt` file:
|
||
|
|
|
||
|
|
```cmake
|
||
|
|
# Typically you don't care so much for a third party library's tests to be
|
||
|
|
# run from your own project's code.
|
||
|
|
set(JSON_BuildTests OFF CACHE INTERNAL "")
|
||
|
|
|
||
|
|
# If you only include this third party in PRIVATE source files, you do not
|
||
|
|
# need to install it when your main project gets installed.
|
||
|
|
# set(JSON_Install OFF CACHE INTERNAL "")
|
||
|
|
|
||
|
|
# Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it
|
||
|
|
# unintended consequences that will break the build. It's generally
|
||
|
|
# discouraged (although not necessarily well documented as such) to use
|
||
|
|
# include(...) for pulling in other CMake projects anyways.
|
||
|
|
add_subdirectory(nlohmann_json)
|
||
|
|
...
|
||
|
|
add_library(foo ...)
|
||
|
|
...
|
||
|
|
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
|
||
|
|
```
|
||
|
|
|
||
|
|
## Embedded (FetchContent)
|
||
|
|
|
||
|
|
Since CMake v3.11,
|
||
|
|
[FetchContent](https://cmake.org/cmake/help/v3.11/module/FetchContent.html) can
|
||
|
|
be used to automatically download the repository as a dependency at configure type.
|
||
|
|
|
||
|
|
Example:
|
||
|
|
```cmake
|
||
|
|
include(FetchContent)
|
||
|
|
|
||
|
|
FetchContent_Declare(json
|
||
|
|
GIT_REPOSITORY https://github.com/nlohmann/json
|
||
|
|
GIT_TAG v3.7.3)
|
||
|
|
|
||
|
|
FetchContent_GetProperties(json)
|
||
|
|
if(NOT json_POPULATED)
|
||
|
|
FetchContent_Populate(json)
|
||
|
|
add_subdirectory(${json_SOURCE_DIR} ${json_BINARY_DIR} EXCLUDE_FROM_ALL)
|
||
|
|
endif()
|
||
|
|
|
||
|
|
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
|
||
|
|
```
|
||
|
|
|
||
|
|
!!! Note
|
||
|
|
The repository <https://github.com/nlohmann/json> download size is huge.
|
||
|
|
It contains all the dataset used for the benchmarks. You might want to depend on
|
||
|
|
a smaller repository. For instance, you might want to replace the URL above by
|
||
|
|
<https://github.com/ArthurSonzogni/nlohmann_json_cmake_fetchcontent>.
|
||
|
|
|
||
|
|
## Supporting Both
|
||
|
|
|
||
|
|
To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin to the following:
|
||
|
|
|
||
|
|
``` cmake
|
||
|
|
# Top level CMakeLists.txt
|
||
|
|
project(FOO)
|
||
|
|
...
|
||
|
|
option(FOO_USE_EXTERNAL_JSON "Use an external JSON library" OFF)
|
||
|
|
...
|
||
|
|
add_subdirectory(thirdparty)
|
||
|
|
...
|
||
|
|
add_library(foo ...)
|
||
|
|
...
|
||
|
|
# Note that the namespaced target will always be available regardless of the
|
||
|
|
# import method
|
||
|
|
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
|
||
|
|
```
|
||
|
|
```cmake
|
||
|
|
# thirdparty/CMakeLists.txt
|
||
|
|
...
|
||
|
|
if(FOO_USE_EXTERNAL_JSON)
|
||
|
|
find_package(nlohmann_json 3.2.0 REQUIRED)
|
||
|
|
else()
|
||
|
|
set(JSON_BuildTests OFF CACHE INTERNAL "")
|
||
|
|
add_subdirectory(nlohmann_json)
|
||
|
|
endif()
|
||
|
|
...
|
||
|
|
```
|
||
|
|
|
||
|
|
`thirdparty/nlohmann_json` is then a complete copy of this source tree.
|