Add Windows _setmode calls to ensure correct character interpretation

include/fmt/format-inl.h

@@ -32,6 +32,8 @@
 #  else
 #    define NOMINMAX
 #    include <windows.h>
+#    include <io.h>
+#    include <fcntl.h>
 #    undef NOMINMAX
 #  endif
 #endif
@@ -186,6 +188,9 @@ FMT_FUNC void report_error(format_func func, int error_code,
                            string_view message) FMT_NOEXCEPT {
   memory_buffer full_message;
   func(full_message, error_code, message);
+#if FMT_USE_WINDOWS_H
+  file_mode_setter mode_setter(stderr, _O_TEXT);
+#endif
   // Use Writer::data instead of Writer::c_str to avoid potential memory
   // allocation.
   fwrite_fully(full_message.data(), 1, full_message.size(), stderr);
@@ -924,6 +929,26 @@ FMT_FUNC void internal::format_windows_error(internal::buffer<char>& out,
   format_error_code(out, error_code, message);
 }
 
+FMT_API FMT_FUNC internal::file_mode_setter::file_mode_setter(std::FILE* f,
+                                                              int mode)
+  FMT_NOEXCEPT : f_(f), fileno_(_fileno(f)), mode_(mode),
+                 prevmode_(_setmode(fileno_, mode)) {
+  // Since _getmode does not exist, we must switch back to the previous mode
+  // in order to flush potentially remaining data in the FILE buffer.
+  if (prevmode_ != -1 && prevmode_ != mode_) {
+    _setmode(fileno_, prevmode_);
+    std::fflush(f_);
+    _setmode(fileno_, mode_);
+  }
+}
+
+FMT_API FMT_FUNC internal::file_mode_setter::~file_mode_setter() FMT_NOEXCEPT {
+  if (prevmode_ != -1 && prevmode_ != mode_) {
+    std::fflush(f_);
+    _setmode(fileno_, prevmode_);
+  }
+}
+
 #endif  // FMT_USE_WINDOWS_H
 
 FMT_FUNC void format_system_error(internal::buffer<char>& out, int error_code,
@@ -971,12 +996,18 @@ FMT_FUNC void vprint(std::FILE* f, string_view format_str, format_args args) {
   memory_buffer buffer;
   internal::vformat_to(buffer, format_str,
                        basic_format_args<buffer_context<char>>(args));
+#if FMT_USE_WINDOWS_H
+  internal::file_mode_setter mode_setter(f, _O_TEXT);
+#endif
   internal::fwrite_fully(buffer.data(), 1, buffer.size(), f);
 }
 
 FMT_FUNC void vprint(std::FILE* f, wstring_view format_str, wformat_args args) {
   wmemory_buffer buffer;
   internal::vformat_to(buffer, format_str, args);
+#if FMT_USE_WINDOWS_H
+  internal::file_mode_setter mode_setter(f, _O_WTEXT);
+#endif
   internal::fwrite_fully(buffer.data(), sizeof(wchar_t), buffer.size(), f);
 }
 

include/fmt/format.h

@@ -927,6 +927,17 @@ class utf16_to_utf8 {
 FMT_API void format_windows_error(fmt::internal::buffer<char>& out,
                                   int error_code,
                                   fmt::string_view message) FMT_NOEXCEPT;
+
+// RAII class to temporarily set the mode of a FILE stream for correct
+// interpretation of character types other than the stream's default.
+class FMT_API file_mode_setter {
+ private:
+  std::FILE* f_;
+  int fileno_, mode_, prevmode_;
+ public:
+  explicit file_mode_setter(std::FILE* f, int mode) FMT_NOEXCEPT;
+  ~file_mode_setter() FMT_NOEXCEPT;
+};
 #endif
 
 template <typename T = void> struct null {};