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Support fmt::runtime with wchar_t in fmt::format_to_n #4715

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Merged
vitaut merged 9 commits into from
Mar 22, 2026
+30 −2
Merged

Support fmt::runtime with wchar_t in fmt::format_to_n #4715

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d7ac9af
Support fmt::runtime with wchar_t in fmt::format_to_n
sunmy2019 Mar 14, 2026
670ddcd
Change runtime_format_string and compile_string from class to struct
sunmy2019 Mar 14, 2026
a7f568e
revert previous fix
sunmy2019 Mar 18, 2026
c138aa2
Refactor format_to_n to use wformat_string
sunmy2019 Mar 18, 2026
1dcff42
Add overload for format_to_n supporting non-char and non-wchar_t outp…
sunmy2019 Mar 20, 2026
ada3f1d
Add tests for format_to and format_to_n with wchar_t, char16_t, and c…
sunmy2019 Mar 20, 2026
dab57dc
Refactor xchar tests to use xchar_helpers for format_to and format_to_n
sunmy2019 Mar 20, 2026
1775d0e
Revert "Refactor xchar tests to use xchar_helpers for format_to and f…
sunmy2019 Mar 20, 2026
acead03
Revert "Add tests for format_to and format_to_n with wchar_t, char16_…
sunmy2019 Mar 20, 2026
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12 changes: 10 additions & 2 deletions include/fmt/xchar.h
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Original file line number Diff line number Diff line change
Expand Up @@ -279,10 +279,18 @@ inline auto vformat_to_n(OutputIt out, size_t n, basic_string_view<Char> fmt,
return {buf.out(), buf.count()};
}

template <typename OutputIt, typename... T,
FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, wchar_t>::value)>
FMT_INLINE auto format_to_n(OutputIt out, size_t n, wformat_string<T...> fmt,
T&&... args) -> format_to_n_result<OutputIt> {
return vformat_to_n(out, n, fmt.get(), fmt::make_wformat_args(args...));
}

template <typename OutputIt, typename S, typename... T,
typename Char = detail::format_string_char_t<S>,
FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, Char>::value&&
detail::is_exotic_char<Char>::value)>
FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, Char>::value &&
!std::is_same<Char, char>::value &&
!std::is_same<Char, wchar_t>::value)>
inline auto format_to_n(OutputIt out, size_t n, const S& fmt, T&&... args)
-> format_to_n_result<OutputIt> {
return vformat_to_n(out, n, fmt::basic_string_view<Char>(fmt),
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20 changes: 20 additions & 0 deletions test/xchar-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,26 @@ TEST(format_test, wide_format_to_n) {
EXPECT_EQ(L"BC x", fmt::wstring_view(buffer, 4));
}

TEST(format_test, wide_format_to_n_runtime) {
wchar_t buffer[4];
buffer[3] = L'x';
auto result = fmt::format_to_n(buffer, 3, fmt::runtime(L"{}"), 12345);
EXPECT_EQ(5u, result.size);
EXPECT_EQ(buffer + 3, result.out);
EXPECT_EQ(L"123x", fmt::wstring_view(buffer, 4));
buffer[0] = L'x';
buffer[1] = L'x';
buffer[2] = L'x';
result = fmt::format_to_n(buffer, 3, fmt::runtime(L"{}"), L'A');
EXPECT_EQ(1u, result.size);
EXPECT_EQ(buffer + 1, result.out);
EXPECT_EQ(L"Axxx", fmt::wstring_view(buffer, 4));
result = fmt::format_to_n(buffer, 3, fmt::runtime(L"{}{} "), L'B', L'C');
EXPECT_EQ(3u, result.size);
EXPECT_EQ(buffer + 3, result.out);
EXPECT_EQ(L"BC x", fmt::wstring_view(buffer, 4));
}

TEST(xchar_test, named_arg_udl) {
using namespace fmt::literals;
auto udl_a =
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