#define JSON_HAS_FILESYSTEM /* value */ #define JSON_HAS_EXPERIMENTAL_FILESYSTEM /* value */
When compiling with C++17, the library provides conversions from and to std::filesystem::path. As compiler support for filesystem is limited, the library tries to detect whether <filesystem>/std::filesystem (JSON_HAS_FILESYSTEM) or <experimental/filesystem>/std::experimental::filesystem (JSON_HAS_EXPERIMENTAL_FILESYSTEM) should be used. To override the built-in check, define JSON_HAS_FILESYSTEM or JSON_HAS_EXPERIMENTAL_FILESYSTEM to 1.
The default value is detected based on the preprocessor macros #!cpp __cpp_lib_filesystem, #!cpp __cpp_lib_experimental_filesystem, #!cpp __has_include(<filesystem>), or #!cpp __has_include(<experimental/filesystem>).
!!! info “Known compiler/stdlib exclusions”
Even when the feature-test macro indicates filesystem support is available, the library disables it on the following broken toolchains: - **MinGW + GCC 8** — disabled entirely (broken `std::filesystem` implementation; [MinGW-w64 bug 737](https://sourceforge.net/p/mingw-w64/bugs/737/)) - **GCC (non-Clang) < 8** — disabled (no filesystem support) - **Clang < 7** — disabled (no filesystem support) - **MSVC < 19.14** — disabled (no filesystem support) - **iOS < 13** — disabled (no filesystem support) - **macOS < Catalina (10.15)** — disabled (no filesystem support) If `JSON_HAS_FILESYSTEM` or `JSON_HAS_EXPERIMENTAL_FILESYSTEM` is `0` despite `__cpp_lib_filesystem` being defined, one of the exclusions above likely applies to your toolchain.
stdc++fs to be linked to for filesystem support.??? example
The code below forces the library to use the header `<experimental/filesystem>`. ```cpp #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1 #include <nlohmann/json.hpp> ... ```