add daily sink filename format

include/spdlog/sinks/daily_file_sink.h

@@ -7,6 +7,7 @@
 #include <spdlog/details/file_helper.h>
 #include <spdlog/details/null_mutex.h>
 #include <spdlog/fmt/fmt.h>
+#include <spdlog/fmt/chrono.h>
 #include <spdlog/sinks/base_sink.h>
 #include <spdlog/details/os.h>
 #include <spdlog/details/circular_q.h>
@@ -36,6 +37,19 @@ struct daily_filename_calculator
     }
 };
 
+/*
+ * Generator of daily log file names by formatting
+ */
+struct daily_filename_format_calculator
+{
+    // Create filename by formatting %Y_%m_%d.log
+    static filename_t calc_filename (const filename_t &filename, const tm &now_tm)
+    {
+        filename_t fmt_filename = fmt::format(SPDLOG_FILENAME_T ("{{:{}}}"), filename);
+        return fmt::format(fmt_filename, now_tm);
+    }
+};
+
 /*
  * Rotating file sink based on date.
  * If truncate != false , the created file will be truncated.
@@ -182,6 +196,8 @@ class daily_file_sink final : public base_sink<Mutex>
 
 using daily_file_sink_mt = daily_file_sink<std::mutex>;
 using daily_file_sink_st = daily_file_sink<details::null_mutex>;
+using daily_file_format_sink_mt = daily_file_sink<std::mutex, daily_filename_format_calculator>;
+using daily_file_format_sink_st = daily_file_sink<details::null_mutex, daily_filename_format_calculator>;
 
 } // namespace sinks
 
@@ -195,10 +211,24 @@ inline std::shared_ptr<logger> daily_logger_mt(
     return Factory::template create<sinks::daily_file_sink_mt>(logger_name, filename, hour, minute, truncate, max_files);
 }
 
+template<typename Factory = spdlog::synchronous_factory>
+inline std::shared_ptr<logger> daily_logger_format_mt(
+    const std::string &logger_name, const filename_t &filename, int hour = 0, int minute = 0, bool truncate = false, uint16_t max_files = 0)
+{
+    return Factory::template create<sinks::daily_file_format_sink_mt>(logger_name, filename, hour, minute, truncate, max_files);
+}
+
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> daily_logger_st(
     const std::string &logger_name, const filename_t &filename, int hour = 0, int minute = 0, bool truncate = false, uint16_t max_files = 0)
 {
     return Factory::template create<sinks::daily_file_sink_st>(logger_name, filename, hour, minute, truncate, max_files);
 }
+
+template<typename Factory = spdlog::synchronous_factory>
+inline std::shared_ptr<logger> daily_logger_format_st(
+    const std::string &logger_name, const filename_t &filename, int hour = 0, int minute = 0, bool truncate = false, uint16_t max_files = 0)
+{
+    return Factory::template create<sinks::daily_file_format_sink_st>(logger_name, filename, hour, minute, truncate, max_files);
+}
 } // namespace spdlog