# Integration

There are several ways to add this header-only library to a C++ project. The following flowchart summarizes how to pick one:

```
flowchart TD
    A[Add the library to a C++ project] --> B{Already using CMake?}
    B -- no --> C{Using pkg-config or plain Makefiles?}
    C -- yes --> D[pkg-config]
    C -- no --> E[Copy the single header]
    B -- yes --> F{Library installed system-wide?}
    F -- yes --> G["find_package()"]
    F -- no --> H{Use a package manager?}
    H -- yes --> I[Package manager]
    H -- no --> J["add_subdirectory() or FetchContent"]
```

- **Copy the single header**, as described [below](#header-only) — no build-system integration required.
- **CMake**: use [`find_package()`](https://json.nlohmann.me/integration/cmake/#external) if the library is already installed, [`add_subdirectory()`](https://json.nlohmann.me/integration/cmake/#embedded) to embed the source tree, or [`FetchContent`](https://json.nlohmann.me/integration/cmake/#fetchcontent) to download it at configure time; see [CMake](https://json.nlohmann.me/integration/cmake/index.md).
- **Package managers**: install the library with a package manager such as Homebrew, Conan, or vcpkg; see [Package Managers](https://json.nlohmann.me/integration/package_managers/index.md).
- **pkg-config**: if you use bare Makefiles instead of CMake, [pkg-config](https://json.nlohmann.me/integration/pkg-config/index.md) can supply the include flags for an already-installed library.

Once the library is integrated, see the [Migration Guide](https://json.nlohmann.me/integration/migration_guide/index.md) for how to keep your code future-proof across releases.

## Header only

[`json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) is the single required file in `single_include/nlohmann` or [released here](https://github.com/nlohmann/json/releases). You need to add

```
#include <nlohmann/json.hpp>

// for convenience
using json = nlohmann::json;
```

to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., `-std=c++11` for GCC and Clang).

You can further use file [`single_include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_fwd.hpp) for forward declarations, and file [`single_include/nlohmann/json_literals.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_literals.hpp) for the user-defined string literals if you define [`JSON_NO_AUTOMATIC_UDLS`](https://json.nlohmann.me/api/macros/json_no_automatic_udls/index.md).