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Convert long doubles under a multi-byte decimal point completely

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The strtold fallback, which is left only for long double formats that
are not binary64 (x87, binary128), substituted the first byte of the
locale's decimal point for '.'. Under a locale whose decimal point is
longer than one byte, such as fa_IR.UTF-8 or ar_EG.UTF-8 (U+066B),
strtold stopped there and the value was truncated at the decimal point.
A longer decimal point is now put into a copy of the token.

The test "locale with a multi-byte decimal point" now compares the long
double values with those of the "C" locale; with x87 long doubles it
failed before.

Fixes #5660.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-30 20:19:11 +02:00
committed by GitHub
parent 44ec53c77b
commit 9c71689715
4 changed files with 101 additions and 65 deletions
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tests/src/unit-locale-cpp.cpp
+11 -6
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@@ -353,8 +353,14 @@ TEST_CASE("locale with a multi-byte decimal point")
// Some locales use a decimal point that is not a single character, e.g.
// U+066B ARABIC DECIMAL SEPARATOR (two bytes in UTF-8). It cannot be
// substituted in place for '.', so the strtold fallback (only for long
// double formats other than binary64) stops early. The conversion must
// still terminate rather than retry forever.
// double formats other than binary64) converts a copy of the token with
// the whole decimal point instead (#5660). The values must be those of the
// "C" locale.
using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
const char* const long_double_numbers = "[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]";
REQUIRE(std::setlocale(LC_NUMERIC, "C") != nullptr);
const long_double_json expected_long_double = long_double_json::parse(long_double_numbers);
const std::array<const char*, 6> names = {{"ar_EG.UTF-8", "ar_SA.UTF-8", "fa_IR.UTF-8", "ps_AF.UTF-8", "ar_EG", "fa_IR"}};
bool tested = false;
for (const char* name : names)
@@ -381,11 +387,10 @@ TEST_CASE("locale with a multi-byte decimal point")
CHECK(j[2] == -0.000123456789012345678);
CHECK(json::accept("3.14159265358979323846"));
// a long double that reaches the strtold fallback must still terminate
using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
// a long double that reaches the strtold fallback is not truncated
long_double_json ld;
CHECK_NOTHROW(ld = long_double_json::parse("[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]"));
CHECK(ld.is_array());
CHECK_NOTHROW(ld = long_double_json::parse(long_double_numbers));
CHECK(ld == expected_long_double);
// a value the locale-independent paths convert is not affected
CHECK(json::parse("12.5") == 12.5);