The number scanner converted its already-validated digit buffer with
std::strtoull/std::strtoll/std::strtod. Those pull in locale and errno
machinery and dominate number-heavy parsing (strtod runs at ~6 M/s).
Replace them with dedicated parsers over the validated buffer:
- parse_integer_unsigned / parse_integer_signed: accumulate digits with
overflow detection, falling back to the float path on overflow exactly
as the strtoull/strtoll round-trip check did. Overflow behavior is
unchanged for narrower or wider custom number types.
- parse_float_fast: Clinger's exact fast path for `double` (<=19 significant
digits, |exp10| <= 22, significand < 2^53), where significand * 10^exp is
exact under IEEE round-to-nearest. This is the same fast path used by
fast_float/simdjson. It is bit-identical to strtod on this subset and
declines (falling back to strtod) otherwise. Only `double` uses it; float
and long double keep std::strtof/std::strtold via a templated overload.
Measured on representative data (g++ 13, -O3):
- integers: DOM parse +11%, SAX +25-34%
- floats: DOM parse +37%, SAX +70% (clang: float DOM ~1.9x)
No dependencies added; header-only and C++11-clean. Existing parser,
lexer, conversion and deserialization unit tests pass unchanged; a
3M-value random-double fuzz matches strtod bit-for-bit.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AXcDtEma2PjxgmPS9cQGzA
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
The diagnostic position of a string value was derived by subtracting the
parsed value's length from the end position. Escape sequences make the
source token longer than the value it parses to, so the reported start
position landed inside the string, one byte off per escape sequence:
input: {"a":"\n\n\n\n\n\n"}
start_pos() == 11, so the reported range covered n\n\n\n"
instead of the documented "\n\n\n\n\n\n"
This contradicts the documented behavior of start_pos(), which is the
position of the opening quote, and it also corrupted the "(bytes N-M)"
part of JSON_DIAGNOSTICS exception messages. Strings with multi-byte
UTF-8 but no escapes were unaffected, which is why this went unnoticed.
Record the offset of the token in the lexer when it starts scanning and
use that, instead of reconstructing it from the parsed value. Booleans,
null and numbers already reported correct positions and are unchanged.
The new lexer member and accessor are compiled only when
JSON_DIAGNOSTIC_POSITIONS is enabled, which is already part of the ABI
tag, so the default build is unaffected.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
`lexer::get()` copied every scanned character into `token_string` on the
whole successful-parse hot path, yet that buffer is consumed only by
`get_token_string()` when rendering the "last read" fragment of a parse
error. On well-formed input the per-byte copy (plus the `unget()` pop)
is pure overhead that is always discarded.
For seekable input adapters - random-access, single-byte iterators such
as those backing `std::string`, `const char*`, and `std::vector<char>` -
the offending token is now reconstructed on demand from the input when
an error is reported, using a saved start offset, and the eager copy is
skipped. Streaming adapters (file, istream, wide-string, and user-defined
adapters) keep the eager copy; the strategy is chosen at compile time via
`input_adapter_supports_seek`, so adapters without the capability are
unaffected.
Error messages are byte-for-byte identical across all adapters, verified
by a new parity regression test. Microbenchmark (4 MB mixed JSON, parsed
from a std::string): ~149 -> ~160 MB/s, about +8%.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
* fix: integer parsed as float when EINTR set in errno
* chore: make amalgamate
* chore: make pretty
---------
Co-authored-by: Stuart Gorman <Stuart.Gorman@kallipr.com>
* Add versioned inline namespace
Add a versioned inline namespace to prevent ABI issues when linking code
using multiple library versions.
* Add namespace macros
* Encode ABI information in inline namespace
Add _diag suffix to inline namespace if JSON_DIAGNOSTICS is enabled, and
_ldvcmp suffix if JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON is enabled.
* Move ABI-affecting macros into abi_macros.hpp
* Move std_fs namespace definition into std_fs.hpp
* Remove std_fs namespace from unit test
* Format more files in tests directory
* Add unit tests
* Update documentation
* Fix GDB pretty printer
* fixup! Add namespace macros
* Derive ABI prefix from NLOHMANN_JSON_VERSION_*
Niels LohmannandClaude Opus 4.8
Colby HaskellandGitHub
Florian AlbrechtskirchingerandGitHub
Niels LohmannandGitHub
Tobias Kux