diff --git a/README.md b/README.md index 013db61868..83a6b5624d 100644 --- a/README.md +++ b/README.md @@ -16,6 +16,8 @@ - [Design goals](#design-goals) - [Integration](#integration) + - [CMake](#cmake) + - [Package Managers](#package-managers) - [Examples](#examples) - [JSON as first-class data type](#json-as-first-class-data-type) - [Serialization / Deserialization](#serialization--deserialization) @@ -69,10 +71,16 @@ to the files you want to process JSON and set the necessary switches to enable C You can further use file [`include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/json_fwd.hpp) for forward-declarations. The installation of json_fwd.hpp (as part of cmake's install step), can be achieved by setting `-DJSON_MultipleHeaders=ON`. -If this library was built with CMake then you can consume it from another CMake project by using the namespaced imported target from the generated package configuration: +### 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 REQUIRED) +find_package(nlohmann_json 3.2.0 REQUIRED) ... add_library(foo ...) ... @@ -80,6 +88,53 @@ 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 "") + +# Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it +# inintended 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) +``` + +#### 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. ### Package Managers