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Niels Lohmann cae5f17f83 📡 Document compiler/stdlib exclusions in macro_scope.hpp

Add "Known compiler/stdlib exclusions" subsections to the public documentation for
JSON_HAS_FILESYSTEM and JSON_HAS_RANGES, listing the exact compiler/stdlib versions
that are silently excluded even when feature-test macros indicate support. Each
exclusion references the originating issue. Also add a pointer note in the compiler
compatibility section linking to these details.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-Authored-By: Claude Code <noreply@anthropic.com>

2026-07-09 08:03:50 +02:00

1.5 KiB

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JSON_HAS_RANGES

#define JSON_HAS_RANGES /* value */

This macro indicates whether the standard library has any support for ranges. Implies support for concepts. Possible values are 1 when supported or 0 when unsupported.

Default definition

The default value is detected based on the preprocessor macro #!cpp __cpp_lib_ranges.

When the macro is not defined, the library will define it to its default value.

Known compiler/stdlib exclusions

Even when the feature-test macro __cpp_lib_ranges indicates ranges support is available, the library disables it on the following incomplete or broken toolchains:

GCC 11.1.0 — disabled (the shipped <ranges> header has a syntax error; issue #4440)
libstdc++ < 11 — disabled (incomplete C++20 ranges support; issue #4440)
Clang < 16 with libstdc++ — disabled (incomplete ranges support; issue #4440)
libc++ < 160000 — disabled (incomplete C++20 ranges support; issue #4440)

If JSON_HAS_RANGES is 0 despite __cpp_lib_ranges being defined, one of the exclusions above likely applies to your toolchain.

Examples

??? example

The code below forces the library to enable support for ranges:

```cpp
#define JSON_HAS_RANGES 1
#include <nlohmann/json.hpp>

...
```

Version history

Added in version 3.11.0.

1.5 KiB Raw Blame History