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Add fmt_print to C API (#4789)

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* Add FMT_FORMAT_ARGS(fmt, ...) macro to C API to simplify user-defined format wrappers

* Add fmt_print to C API
This commit is contained in:
Ferdinand Bachmann 2026-06-05 15:40:30 +02:00 committed by GitHub
parent 9afcd929ba
commit ffd8397db1
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GPG Key ID: B5690EEEBB952194
2 changed files with 43 additions and 10 deletions
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19
include/fmt/fmt-c.h
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@ -10,6 +10,7 @@
#include <stdbool.h> // bool #include <stdbool.h> // bool
#include <stddef.h> // size_t #include <stddef.h> // size_t
#include <stdio.h> // FILE
#ifdef __cplusplus #ifdef __cplusplus
extern "C" { extern "C" {
@ -46,6 +47,8 @@ enum { fmt_error = -1, fmt_error_invalid_arg = -2 };
int fmt_vformat(char* buffer, size_t size, const char* fmt, const fmt_arg* args, int fmt_vformat(char* buffer, size_t size, const char* fmt, const fmt_arg* args,
size_t num_args); size_t num_args);
int fmt_vprint(FILE* stream, const char* fmt, const fmt_arg* args,
size_t num_args);
#ifdef __cplusplus #ifdef __cplusplus
} }
@ -181,11 +184,17 @@ typedef enum {} fmt_signed_char;
(fmt_arg[]) { FMT_MAP(FMT_MAKE_ARG, ##__VA_ARGS__) } (fmt_arg[]) { FMT_MAP(FMT_MAKE_ARG, ##__VA_ARGS__) }
# define FMT_EXPAND(v) v # define FMT_EXPAND(v) v
# define fmt_format(buffer, size, fmt, ...) \ # define FMT_FORMAT_ARGS(fmt, ...) \
fmt_vformat((buffer), (size), (fmt), \ (fmt), \
FMT_EXPAND(FMT_VA_SELECT(FMT_MAKE_NULL, FMT_MAKE_ARGLIST, \ FMT_EXPAND(FMT_VA_SELECT(FMT_MAKE_NULL, FMT_MAKE_ARGLIST, \
##__VA_ARGS__)(__VA_ARGS__)), \ ##__VA_ARGS__)(__VA_ARGS__)), \
FMT_NARG(, ##__VA_ARGS__)) FMT_NARG(, ##__VA_ARGS__)
# define fmt_format(buffer, size, fmt, ...) \
fmt_vformat((buffer), (size), FMT_FORMAT_ARGS((fmt), ##__VA_ARGS__))
# define fmt_print(stream, fmt, ...) \
fmt_vprint((stream), FMT_FORMAT_ARGS((fmt), ##__VA_ARGS__))
#endif // __cplusplus #endif // __cplusplus

34
src/fmt-c.cc
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@ -9,12 +9,12 @@
#include <fmt/base.h> #include <fmt/base.h>
extern "C" int fmt_vformat(char* buffer, size_t size, const char* fmt, constexpr size_t max_c_format_args = 16;
const fmt_arg* args, size_t num_args) { static int convert_c_format_args(
constexpr size_t max_args = 16; fmt::basic_format_arg<fmt::format_context>* format_args,
if (num_args > max_args) return fmt_error_invalid_arg; const fmt_arg* args, size_t num_args) {
if (num_args > max_c_format_args) return fmt_error_invalid_arg;
fmt::basic_format_arg<fmt::format_context> format_args[max_args];
for (size_t i = 0; i < num_args; ++i) { for (size_t i = 0; i < num_args; ++i) {
switch (args[i].type) { switch (args[i].type) {
case fmt_int: format_args[i] = args[i].value.int_value; break; case fmt_int: format_args[i] = args[i].value.int_value; break;
@ -31,6 +31,15 @@ extern "C" int fmt_vformat(char* buffer, size_t size, const char* fmt,
default: return fmt_error_invalid_arg; default: return fmt_error_invalid_arg;
} }
} }
return 0;
}
extern "C" int fmt_vformat(char* buffer, size_t size, const char* fmt,
const fmt_arg* args, size_t num_args) {
fmt::basic_format_arg<fmt::format_context> format_args[max_c_format_args];
int error = convert_c_format_args(format_args, args, num_args);
if (error != 0) return error;
FMT_TRY { FMT_TRY {
auto result = fmt::vformat_to_n( auto result = fmt::vformat_to_n(
buffer, size, fmt, buffer, size, fmt,
@ -40,3 +49,18 @@ extern "C" int fmt_vformat(char* buffer, size_t size, const char* fmt,
FMT_CATCH(...) {} FMT_CATCH(...) {}
return fmt_error; return fmt_error;
} }
extern "C" int fmt_vprint(FILE* stream, const char* fmt, const fmt_arg* args,
size_t num_args) {
fmt::basic_format_arg<fmt::format_context> format_args[max_c_format_args];
int error = convert_c_format_args(format_args, args, num_args);
if (error != 0) return error;
FMT_TRY {
fmt::vprint(stream, fmt,
fmt::format_args(format_args, static_cast<int>(num_args)));
return 0;
}
FMT_CATCH(...) {}
return fmt_error;
}