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nlohmann
48 lines
2.2 KiB
Markdown
48 lines
2.2 KiB
Markdown
# JSON_HAS_FILESYSTEM / JSON_HAS_EXPERIMENTAL_FILESYSTEM
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```
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#define JSON_HAS_FILESYSTEM /* value */
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#define JSON_HAS_EXPERIMENTAL_FILESYSTEM /* value */
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```
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When compiling with C++17, the library provides conversions from and to [`std::filesystem::path`](https://en.cppreference.com/w/cpp/filesystem/path). As compiler support for filesystem is limited, the library tries to detect whether [`<filesystem>`/`std::filesystem`](https://en.cppreference.com/w/cpp/header/filesystem) (`JSON_HAS_FILESYSTEM`) or [`<experimental/filesystem>`/`std::experimental::filesystem`](https://en.cppreference.com/w/cpp/header/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`.
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## Default definition
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The default value is detected based on the preprocessor macros `__cpp_lib_filesystem`, `__cpp_lib_experimental_filesystem`, `__has_include(<filesystem>)`, or `__has_include(<experimental/filesystem>)`.
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Known compiler/stdlib exclusions
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Even when the feature-test macro indicates filesystem support is available, the library disables it on the following broken toolchains:
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- **MinGW + GCC 8** — disabled entirely (broken `std::filesystem` implementation; [MinGW-w64 bug 737](https://sourceforge.net/p/mingw-w64/bugs/737/))
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- **GCC (non-Clang) < 8** — disabled (no filesystem support)
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- **Clang < 7** — disabled (no filesystem support)
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- **MSVC < 19.14** — disabled (no filesystem support)
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- **iOS < 13** — disabled (no filesystem support)
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- **macOS < Catalina (10.15)** — disabled (no filesystem support)
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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.
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## Notes
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- Note that older compilers or older versions of libstdc++ also require the library `stdc++fs` to be linked to for filesystem support.
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- Both macros are undefined outside the library.
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## Examples
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Example
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The code below forces the library to use the header `<experimental/filesystem>`.
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```
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#define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
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#include <nlohmann/json.hpp>
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...
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```
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## Version history
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- Added in version 3.10.5.
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