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Add FMT_STATIC_FORMAT

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This commit is contained in:
Victor Zverovich 2025-09-01 07:42:57 -07:00
parent a57f196cad
commit 02fb76d69b
2 changed files with 50 additions and 16 deletions
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34
include/fmt/compile.h
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@ -525,6 +525,40 @@ void print(const S& fmt, T&&... args) {
print(stdout, fmt, std::forward<T>(args)...); print(stdout, fmt, std::forward<T>(args)...);
} }
template <size_t N> class static_format_result {
private:
char data[N];
public:
template <typename S, typename... T,
FMT_ENABLE_IF(is_compiled_string<S>::value)>
explicit FMT_CONSTEXPR static_format_result(const S& fmt, T&&... args) {
*fmt::format_to(data, fmt, std::forward<T>(args)...) = '\0';
}
auto str() const -> fmt::string_view { return {data, N - 1}; }
auto c_str() const -> const char* { return data; }
};
/**
* Formats arguments according to the format string `fmt_str` and produces
* a string of the exact required size at compile time. Both the format string
* and the arguments must be compile-time expressions.
*
* The resulting string can be accessed as a C string via `c_str()` or as
* a `fmt::string_view` via `str()`.
*
* **Example**:
*
* // Produces the static string "42" at compile time.
* static constexpr auto result = FMT_STATIC_FORMAT("{}", 42);
* const char* s = result.c_str();
*/
#define FMT_STATIC_FORMAT(fmt_str, ...) \
fmt::static_format_result< \
fmt::formatted_size(FMT_COMPILE(fmt_str), __VA_ARGS__) + 1>( \
FMT_COMPILE(fmt_str), __VA_ARGS__)
#if FMT_USE_NONTYPE_TEMPLATE_ARGS #if FMT_USE_NONTYPE_TEMPLATE_ARGS
inline namespace literals { inline namespace literals {
template <detail::fixed_string Str> constexpr auto operator""_cf() { template <detail::fixed_string Str> constexpr auto operator""_cf() {

32
test/compile-test.cc
View File

@ -236,6 +236,12 @@ TEST(compile_test, constexpr_formatted_size) {
fmt::formatted_size(FMT_COMPILE("{:s}"), "abc"); fmt::formatted_size(FMT_COMPILE("{:s}"), "abc");
EXPECT_EQ(str_size, 3); EXPECT_EQ(str_size, 3);
} }
TEST(compile_test, static_format) {
constexpr auto result = FMT_STATIC_FORMAT("{}", 42);
EXPECT_STREQ(result.c_str(), "42");
EXPECT_EQ(result.str(), "42");
}
# endif # endif
TEST(compile_test, text_and_arg) { TEST(compile_test, text_and_arg) {
@ -423,22 +429,16 @@ TEST(compile_time_formatting_test, multibyte_fill) {
#endif #endif
#if FMT_USE_CONSTEXPR_STRING #if FMT_USE_CONSTEXPR_STRING
TEST(compile_test, constexpr_string_format) {
constexpr auto result = []() {
return fmt::format(FMT_COMPILE("{}"), 42) == "42";
}();
EXPECT_TRUE(result);
TEST(compile_test, constexpr_format) { // Test with a larger string to avoid small string optimization.
{ constexpr auto big = []() {
constexpr auto result = []() { return fmt::format(FMT_COMPILE("{:100}"), ' ') == std::string(100, ' ');
return fmt::format(FMT_COMPILE("{}"), 42) == "42"; }();
}(); EXPECT_TRUE(big);
EXPECT_TRUE(result);
}
{
// Test with a larger string to avoid small string optimization.
constexpr auto result = []() {
return fmt::format(FMT_COMPILE("{:100}"), ' ') == std::string(100, ' ');
}();
EXPECT_TRUE(result);
}
} }
#endif // FMT_USE_CONSTEXPR_STRING #endif // FMT_USE_CONSTEXPR_STRING