Niels Lohmann
c7b77ed23d
Both macros select between definitions of the same inline functions, so translation units that disagree on them violated the ODR. Like the other ABI-affecting macros, they now add a tag to the inline namespace (_vns and _vssse3), and the docs replace the "Define consistently" warning with the usual ABI compatibility note. From gregmarr's review of #5628. nlohmann_json.natvis covers twice as many tags now, so it lists four times as many namespaces (14.7 MB instead of 3.4 MB). Signed-off-by: Niels Lohmann <mail@nlohmann.me>
1.7 KiB
JSON_VIEW_NO_SIMD
#define JSON_VIEW_NO_SIMD
When defined, the parser of basic_json_document (<nlohmann/json_view.hpp>)
uses only portable C++ to scan strings. By default, it scans long runs of string bytes 16 at a time with NEON on
AArch64 (with GCC and Clang) and SSE2 on x86-64, which are part of the baseline instruction sets of these
architectures, and validates non-ASCII text with NEON (or SSSE3, see
JSON_VIEW_USE_SSSE3).
The same input is accepted or rejected either way, with the same values, and errors are reported the same way; only the speed differs. The macro exists for platforms whose compilers lack the intrinsics headers, and to test the portable code.
!!! note "ABI compatibility"
The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the
[namespace](../../features/namespace.md) (tag `_vns`), resulting in distinct symbol names. Translation units
compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR)
violations, but they cannot exchange instances of library types.
Default definition
By default, #!cpp JSON_VIEW_NO_SIMD is not defined, and the vector code is used where available.
#undef JSON_VIEW_NO_SIMD
Examples
??? example
The code below uses the portable string scanning of the view.
```cpp
#define JSON_VIEW_NO_SIMD
#include <nlohmann/json_view.hpp>
...
```
See also
- JSON_VIEW_USE_SSSE3 - validate non-ASCII strings with SSSE3 on x86-64
- json_view - the zero-copy view
Version history
- Added in version 3.13.0.