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Fix flushing C++ iostreams before calling write_console() (fmtlib#3689)
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This change correctly implements https://wg21.link/P2539/ for both
C streams and C++ iostreams.

Fixes fmtlib#3688.
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dimztimz authored and ckerr committed Nov 7, 2023
1 parent 4ae16a6 commit 67cbc0d
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Showing 3 changed files with 33 additions and 16 deletions.
16 changes: 10 additions & 6 deletions include/fmt/format-inl.h
Original file line number Diff line number Diff line change
Expand Up @@ -1425,16 +1425,13 @@ FMT_FUNC std::string vformat(string_view fmt, format_args args) {

namespace detail {
#if !defined(_WIN32) || defined(FMT_WINDOWS_NO_WCHAR)
FMT_FUNC bool write_console(std::FILE*, string_view) { return false; }
FMT_FUNC bool write_console(int, string_view) { return false; }
#else
using dword = conditional_t<sizeof(long) == 4, unsigned long, unsigned>;
extern "C" __declspec(dllimport) int __stdcall WriteConsoleW( //
void*, const void*, dword, dword*, void*);

FMT_FUNC bool write_console(std::FILE* f, string_view text) {
int fd = _fileno(f);
if (!_isatty(fd)) return false;
std::fflush(f);
FMT_FUNC bool write_console(int fd, string_view text) {
auto u16 = utf8_to_utf16(text);
return WriteConsoleW(reinterpret_cast<void*>(_get_osfhandle(fd)), u16.c_str(),
static_cast<dword>(u16.size()), nullptr, nullptr) != 0;
Expand All @@ -1451,7 +1448,14 @@ FMT_FUNC void vprint_mojibake(std::FILE* f, string_view fmt, format_args args) {
#endif

FMT_FUNC void print(std::FILE* f, string_view text) {
if (!write_console(f, text)) fwrite_fully(text.data(), text.size(), f);
#ifdef _WIN32
int fd = _fileno(f);
if (_isatty(fd)) {
std::fflush(f);
if (write_console(fd, text)) return;
}
#endif
fwrite_fully(text.data(), text.size(), f);
}
} // namespace detail

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2 changes: 1 addition & 1 deletion include/fmt/format.h
Original file line number Diff line number Diff line change
Expand Up @@ -1038,7 +1038,7 @@ struct is_contiguous<basic_memory_buffer<T, SIZE, Allocator>> : std::true_type {

FMT_END_EXPORT
namespace detail {
FMT_API bool write_console(std::FILE* f, string_view text);
FMT_API bool write_console(int fd, string_view text);
FMT_API void print(std::FILE*, string_view);
} // namespace detail

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31 changes: 22 additions & 9 deletions include/fmt/ostream.h
Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,12 @@

#include <fstream> // std::filebuf

#if defined(_WIN32) && defined(__GLIBCXX__)
# include <ext/stdio_filebuf.h>
# include <ext/stdio_sync_filebuf.h>
#ifdef _WIN32
# ifdef __GLIBCXX__
# include <ext/stdio_filebuf.h>
# include <ext/stdio_sync_filebuf.h>
# endif
# include <io.h>
#endif

#include "format.h"
Expand All @@ -38,21 +41,31 @@ auto get_file(std::filebuf&) -> FILE*;
#endif

inline bool write_ostream_unicode(std::ostream& os, fmt::string_view data) {
FILE* f = nullptr;
#if FMT_MSC_VERSION
if (auto* buf = dynamic_cast<std::filebuf*>(os.rdbuf()))
if (FILE* f = get_file(*buf)) return write_console(f, data);
f = get_file(*buf);
else
return false;
#elif defined(_WIN32) && defined(__GLIBCXX__)
auto* rdbuf = os.rdbuf();
FILE* c_file;
if (auto* sfbuf = dynamic_cast<__gnu_cxx::stdio_sync_filebuf<char>*>(rdbuf))
c_file = sfbuf->file();
f = sfbuf->file();
else if (auto* fbuf = dynamic_cast<__gnu_cxx::stdio_filebuf<char>*>(rdbuf))
c_file = fbuf->file();
f = fbuf->file();
else
return false;
if (c_file) return write_console(c_file, data);
#else
ignore_unused(os, data);
ignore_unused(os, data, f);
#endif
#ifdef _WIN32
if (f) {
int fd = _fileno(f);
if (_isatty(fd)) {
os.flush();
return write_console(fd, data);
}
}
#endif
return false;
}
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