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Keep thousands_sep/decimal_point const via a small locale_chars struct

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const members can't be assigned in a constructor body, so seeding them
from std::localeconv() meant either dropping const or holding onto the
lconv* for longer than needed. A sub-object computes both from the
pointer in its own constructor and is itself initialized in serializer's
mem-initializer-list, so the two chars stay const, std::localeconv() is
still called exactly once, and nothing outlives the constructor.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-10 18:58:22 +02:00
parent 6155d5242f
commit 772e44ff97
2 changed files with 44 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/nlohmann/detail/output/serializer.hpp
+22 -15
View File
@@ -82,18 +82,13 @@ class serializer
const std::size_t indent_step_ = 0,
error_handler_t error_handler_ = error_handler_t::strict)
: o(std::move(s))
, locale(std::localeconv())
, indent_char(ichar)
, pretty_print(pretty_print_)
, ensure_ascii(ensure_ascii_)
, indent_step(indent_step_)
, error_handler(error_handler_)
{
// only used here to seed thousands_sep/decimal_point, so a local
// suffices and the serializer does not need to hold onto it
const auto* loc = std::localeconv();
thousands_sep = loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep));
decimal_point = loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point));
}
{}
// deleted because of pointer members
serializer(const serializer&) = delete;
@@ -1552,20 +1547,20 @@ class serializer
JSON_ASSERT(static_cast<std::size_t>(len) < number_buffer.size());
// erase thousands separators
if (thousands_sep != '\0')
if (locale.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);
const auto end = std::remove(number_buffer.begin(), number_buffer.begin() + len, locale.thousands_sep);
std::fill(end, number_buffer.end(), '\0');
JSON_ASSERT((end - number_buffer.begin()) <= len);
len = (end - number_buffer.begin());
}
// convert decimal point to '.'
if (decimal_point != '\0' && decimal_point != '.')
if (locale.decimal_point != '\0' && locale.decimal_point != '.')
{
// 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);
const auto dec_pos = std::find(number_buffer.begin(), number_buffer.end(), locale.decimal_point);
if (dec_pos != number_buffer.end())
{
*dec_pos = '.';
@@ -1671,16 +1666,28 @@ class serializer
}
private:
/// the locale's thousand separator and decimal point characters
struct locale_chars
{
explicit locale_chars(const std::lconv* loc) noexcept
: thousands_sep(loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep)))
, decimal_point(loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point)))
{}
const char thousands_sep;
const char decimal_point;
};
/// the output of the serializer
output_adapter_t<char> o = nullptr;
/// a (hopefully) large enough character buffer
std::array<char, 64> number_buffer{{}};
/// the locale's thousand separator character
char thousands_sep = '\0';
/// the locale's decimal point character
char decimal_point = '\0';
/// computed once from std::localeconv() at construction; @ref
/// locale_chars keeps std::localeconv()'s pointer from having to be held
/// past the constructor, while still letting these stay const
const locale_chars locale;
/// string buffer
std::array<char, 512> string_buffer{{}};
single_include/nlohmann/json.hpp
+22 -15
View File
@@ -21430,18 +21430,13 @@ class serializer
const std::size_t indent_step_ = 0,
error_handler_t error_handler_ = error_handler_t::strict)
: o(std::move(s))
, locale(std::localeconv())
, indent_char(ichar)
, pretty_print(pretty_print_)
, ensure_ascii(ensure_ascii_)
, indent_step(indent_step_)
, error_handler(error_handler_)
{
// only used here to seed thousands_sep/decimal_point, so a local
// suffices and the serializer does not need to hold onto it
const auto* loc = std::localeconv();
thousands_sep = loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep));
decimal_point = loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point));
}
{}
// deleted because of pointer members
serializer(const serializer&) = delete;
@@ -22900,20 +22895,20 @@ class serializer
JSON_ASSERT(static_cast<std::size_t>(len) < number_buffer.size());
// erase thousands separators
if (thousands_sep != '\0')
if (locale.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);
const auto end = std::remove(number_buffer.begin(), number_buffer.begin() + len, locale.thousands_sep);
std::fill(end, number_buffer.end(), '\0');
JSON_ASSERT((end - number_buffer.begin()) <= len);
len = (end - number_buffer.begin());
}
// convert decimal point to '.'
if (decimal_point != '\0' && decimal_point != '.')
if (locale.decimal_point != '\0' && locale.decimal_point != '.')
{
// 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);
const auto dec_pos = std::find(number_buffer.begin(), number_buffer.end(), locale.decimal_point);
if (dec_pos != number_buffer.end())
{
*dec_pos = '.';
@@ -23019,16 +23014,28 @@ class serializer
}
private:
/// the locale's thousand separator and decimal point characters
struct locale_chars
{
explicit locale_chars(const std::lconv* loc) noexcept
: thousands_sep(loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep)))
, decimal_point(loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point)))
{}
const char thousands_sep;
const char decimal_point;
};
/// the output of the serializer
output_adapter_t<char> o = nullptr;
/// a (hopefully) large enough character buffer
std::array<char, 64> number_buffer{{}};
/// the locale's thousand separator character
char thousands_sep = '\0';
/// the locale's decimal point character
char decimal_point = '\0';
/// computed once from std::localeconv() at construction; @ref
/// locale_chars keeps std::localeconv()'s pointer from having to be held
/// past the constructor, while still letting these stay const
const locale_chars locale;
/// string buffer
std::array<char, 512> string_buffer{{}};