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Replace a multibyte decimal point in dump() of a long double (#5993)

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The snprintf path of dump_float(), used when number_float_t is neither
IEEE single nor double (a long double on x86-64 and aarch64 Linux), read
localeconv()->decimal_point and ->thousands_sep as single chars. Under a
locale with a multibyte decimal point (glibc's ps_AF: U+066B), it removed
the first byte as a "thousands separator" and left the second one in the
output, so 1.5L dumped as "1\xab5.0".

Find the whole decimal point with std::search and replace it with '.',
as the parser already does since #5660. Drop the thousands-separator
removal: %g never groups digits.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-11-01 22:48:42 +01:00
1 parent b2674a4a2f
commit 3720e4b3aa
3 files changed
+46 -40
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include/nlohmann/detail/output/serializer.hpp
+19 -20
View File
@@ -8,14 +8,14 @@
#pragma once
#include <algorithm> // remove, fill, find, none_of, min
#include <algorithm> // copy, none_of, min, search
#include <array> // array
#include <clocale> // localeconv, lconv
#include <cmath> // isfinite
#include <cstddef> // size_t, ptrdiff_t
#include <cstdint> // uint8_t
#include <cstdio> // snprintf
#include <cstring> // memcpy, memset
#include <cstring> // memcpy, memset, strlen
#include <iterator> // next
#include <limits> // numeric_limits
#include <string> // string, char_traits
@@ -2095,31 +2095,30 @@ class serializer
// check if the buffer was large enough
JSON_ASSERT(static_cast<std::size_t>(len) < number_buffer.size());
// look up the locale's thousands separator and decimal point now,
// matching what snprintf_float() just used (see lexer::get_decimal_point())
// look up the locale's decimal point now, matching what
// snprintf_float() just used (see lexer::get_decimal_point()); it is a
// string, which can be longer than one byte (U+066B in ps_AF, #5993).
// A thousands separator needs no handling: %g never groups digits.
const auto* loc = std::localeconv();
JSON_ASSERT(loc != nullptr);
const char thousands_sep = (loc->thousands_sep == nullptr) ? '\0' : *loc->thousands_sep;
const char decimal_point = (loc->decimal_point == nullptr) ? '\0' : *loc->decimal_point;
// erase thousands separators
if (thousands_sep != '\0')
{
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::remove returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto end = std::remove(number_buffer.begin(), number_buffer.begin() + len, thousands_sep);
std::fill(end, number_buffer.end(), '\0');
JSON_ASSERT((end - number_buffer.begin()) <= len);
len = (end - number_buffer.begin());
}
const char* const decimal_point = (loc->decimal_point == nullptr) ? "" : loc->decimal_point;
const std::size_t decimal_point_len = std::strlen(decimal_point);
// convert decimal point to '.'
if (decimal_point != '\0' && decimal_point != '.')
if (decimal_point_len != 0 && !(decimal_point_len == 1 && decimal_point[0] == '.'))
{
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::find returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto dec_pos = std::find(number_buffer.begin(), number_buffer.end(), decimal_point);
if (dec_pos != number_buffer.end())
const auto first = number_buffer.begin();
const auto last = first + len;
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::search returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto dec_pos = std::search(first, last, decimal_point, decimal_point + decimal_point_len);
if (dec_pos != last)
{
*dec_pos = '.';
// move the fraction and exponent behind the '.' (a no-op for a one-byte decimal point)
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::copy returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto end = std::copy(dec_pos + static_cast<std::ptrdiff_t>(decimal_point_len), last, dec_pos + 1);
*end = '\0';
len = end - first;
}
}
single_include/nlohmann/json.hpp
Generated
+19 -20
View File
@@ -33473,14 +33473,14 @@ NLOHMANN_JSON_NAMESPACE_END
#include <algorithm> // remove, fill, find, none_of, min
#include <algorithm> // copy, none_of, min, search
#include <array> // array
#include <clocale> // localeconv, lconv
#include <cmath> // isfinite
#include <cstddef> // size_t, ptrdiff_t
#include <cstdint> // uint8_t
#include <cstdio> // snprintf
#include <cstring> // memcpy, memset
#include <cstring> // memcpy, memset, strlen
#include <iterator> // next
#include <limits> // numeric_limits
#include <string> // string, char_traits
@@ -37342,31 +37342,30 @@ class serializer
// check if the buffer was large enough
JSON_ASSERT(static_cast<std::size_t>(len) < number_buffer.size());
// look up the locale's thousands separator and decimal point now,
// matching what snprintf_float() just used (see lexer::get_decimal_point())
// look up the locale's decimal point now, matching what
// snprintf_float() just used (see lexer::get_decimal_point()); it is a
// string, which can be longer than one byte (U+066B in ps_AF, #5993).
// A thousands separator needs no handling: %g never groups digits.
const auto* loc = std::localeconv();
JSON_ASSERT(loc != nullptr);
const char thousands_sep = (loc->thousands_sep == nullptr) ? '\0' : *loc->thousands_sep;
const char decimal_point = (loc->decimal_point == nullptr) ? '\0' : *loc->decimal_point;
// erase thousands separators
if (thousands_sep != '\0')
{
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::remove returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto end = std::remove(number_buffer.begin(), number_buffer.begin() + len, thousands_sep);
std::fill(end, number_buffer.end(), '\0');
JSON_ASSERT((end - number_buffer.begin()) <= len);
len = (end - number_buffer.begin());
}
const char* const decimal_point = (loc->decimal_point == nullptr) ? "" : loc->decimal_point;
const std::size_t decimal_point_len = std::strlen(decimal_point);
// convert decimal point to '.'
if (decimal_point != '\0' && decimal_point != '.')
if (decimal_point_len != 0 && !(decimal_point_len == 1 && decimal_point[0] == '.'))
{
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::find returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto dec_pos = std::find(number_buffer.begin(), number_buffer.end(), decimal_point);
if (dec_pos != number_buffer.end())
const auto first = number_buffer.begin();
const auto last = first + len;
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::search returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto dec_pos = std::search(first, last, decimal_point, decimal_point + decimal_point_len);
if (dec_pos != last)
{
*dec_pos = '.';
// move the fraction and exponent behind the '.' (a no-op for a one-byte decimal point)
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::copy returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto end = std::copy(dec_pos + static_cast<std::ptrdiff_t>(decimal_point_len), last, dec_pos + 1);
*end = '\0';
len = end - first;
}
}
tests/src/unit-locale-cpp.cpp
+8
View File
@@ -397,6 +397,14 @@ TEST_CASE("locale with a multi-byte decimal point")
// a value the locale-independent paths convert is not affected
CHECK(json::parse("12.5") == 12.5);
// dump() of a long double that takes the snprintf path replaces the
// whole decimal point, not only its first byte (#5993)
CHECK(long_double_json(1.5L).dump() == "1.5");
CHECK(long_double_json(2.0L).dump() == "2.0");
CHECK(long_double_json(-0.25L).dump() == "-0.25");
CHECK(long_double_json::parse(long_double_json(1.5e-7L).dump()) == long_double_json(1.5e-7L));
CHECK(long_double_json::parse(ld.dump()) == expected_long_double);
}
if (!tested)
{