Fix support for wchar to utf8 under windows (fix issue #851 and #764)

include/spdlog/details/logger_impl.h

@@ -175,6 +175,29 @@ inline void spdlog::logger::critical(const T &msg)
 }
 
 #ifdef SPDLOG_WCHAR_TO_UTF8_SUPPORT
+static_assert(_WIN32, "SPDLOG_WCHAR_TO_UTF8_SUPPORT only supported on windows");
+inline void wbuf_to_utf8buf(const fmt::wmemory_buffer &wbuf, fmt::memory_buffer &target)
+{
+    int wbuf_size = static_cast<int>(wbuf.size());
+    if (wbuf_size == 0)
+    {
+        return;
+    }
+
+    auto result_size = ::WideCharToMultiByte(CP_UTF8, 0, wbuf.data(), wbuf_size, NULL, 0, NULL, NULL);
+    
+    if (result_size > 0)
+    {
+        target.resize(result_size);
+        ::WideCharToMultiByte(CP_UTF8, 0, wbuf.data(), wbuf_size, &target.data()[0], result_size, NULL, NULL);
+    }
+    else
+    {
+        throw spdlog::spdlog_ex("Failed converting to utf8", errno);
+    }
+}
+
+
 template<typename... Args>
 inline void spdlog::logger::log(level::level_enum lvl, const wchar_t *fmt, const Args &... args)
 {
@@ -183,15 +206,14 @@ inline void spdlog::logger::log(level::level_enum lvl, const wchar_t *fmt, const
         return;
     }
 
-    decltype(wstring_converter_)::byte_string utf8_string;
-
     try
     {
-        {
-            std::lock_guard<std::mutex> lock(wstring_converter_mutex_);
-            utf8_string = wstring_converter_.to_bytes(fmt);
-        }
-        log(lvl, utf8_string.c_str(), args...);
+		// format to wmemory_buffer and convert to utf8
+        details::log_msg log_msg(&name_, lvl);
+        fmt::wmemory_buffer wbuf;
+        fmt::format_to(wbuf, fmt, args...);        		
+        wbuf_to_utf8buf(wbuf, log_msg.raw);
+        sink_it_(log_msg);
     }
     SPDLOG_CATCH_AND_HANDLE
 }

include/spdlog/logger.h

@@ -25,6 +25,7 @@
 #include <memory>
 #include <string>
 #include <vector>
+#include <locale>
 
 namespace spdlog {
 
@@ -146,8 +147,7 @@ protected:
     // message/minute
     void default_err_handler_(const std::string &msg);
 
-    // increment the message count (only if
-    // defined(SPDLOG_ENABLE_MESSAGE_COUNTER))
+    // increment the message count (only if defined(SPDLOG_ENABLE_MESSAGE_COUNTER))
     void incr_msg_counter_(details::log_msg &msg);
 
     const std::string name_;
@@ -157,11 +157,6 @@ protected:
     log_err_handler err_handler_;
     std::atomic<time_t> last_err_time_;
     std::atomic<size_t> msg_counter_;
-
-#ifdef SPDLOG_WCHAR_TO_UTF8_SUPPORT
-    std::wstring_convert<std::codecvt_utf8<wchar_t>> wstring_converter_;
-    std::mutex wstring_converter_mutex_;
-#endif
 };
 } // namespace spdlog