separate std string view from std format

CMakeLists.txt

@@ -25,7 +25,7 @@ endif()
 # ---------------------------------------------------------------------------------------
 # Compiler config
 # ---------------------------------------------------------------------------------------
-if(SPDLOG_USE_STD_FORMAT)
+if(SPDLOG_USE_STD_FORMAT OR SPDLOG_USE_STD_STRING_VIEW)
     set(CMAKE_CXX_STANDARD 20)
     set(CMAKE_CXX_STANDARD_REQUIRED ON)
 elseif(NOT CMAKE_CXX_STANDARD)
@@ -88,6 +88,7 @@ option(SPDLOG_BUILD_WARNINGS "Enable compiler warnings" OFF)
 option(SPDLOG_SYSTEM_INCLUDES "Include as system headers (skip for clang-tidy)." OFF)
 option(SPDLOG_INSTALL "Generate the install target" ${SPDLOG_MASTER_PROJECT})
 option(SPDLOG_USE_STD_FORMAT "Use std::format instead of fmt library." OFF)
+option(SPDLOG_USE_STD_STRING_VIEW "Use std::string_view instead of the fmt implementation of string_view." OFF)
 option(SPDLOG_FMT_EXTERNAL "Use external fmt library instead of bundled" OFF)
 option(SPDLOG_FMT_EXTERNAL_HO "Use external fmt header-only library instead of bundled" OFF)
 option(SPDLOG_NO_EXCEPTIONS "Compile with -fno-exceptions. Call abort() on any spdlog exceptions" OFF)
@@ -104,6 +105,10 @@ if(SPDLOG_USE_STD_FORMAT AND SPDLOG_FMT_EXTERNAL)
     message(FATAL_ERROR "SPDLOG_USE_STD_FORMAT and SPDLOG_FMT_EXTERNAL are mutually exclusive")
 endif()
 
+if(SPDLOG_USE_STD_FORMAT AND NOT SPDLOG_USE_STD_STRING_VIEW)
+    message(FATAL_ERROR "SPDLOG_USE_STD_FORMAT requires SPDLOG_USE_STD_STRING_VIEW")
+endif()
+
 # misc tweakme options
 if(WIN32)
     option(SPDLOG_WCHAR_SUPPORT "Support wchar api" OFF)
@@ -248,6 +253,7 @@ foreach(
     SPDLOG_NO_TLS
     SPDLOG_NO_ATOMIC_LEVELS
     SPDLOG_DISABLE_DEFAULT_LOGGER
+    SPDLOG_USE_STD_STRING_VIEW
     SPDLOG_USE_STD_FORMAT)
     if(${SPDLOG_OPTION})
         target_compile_definitions(spdlog PUBLIC ${SPDLOG_OPTION})

example/example.cpp

@@ -279,7 +279,7 @@ struct fmt::formatter<my_type> : fmt::formatter<std::string>
 {
     auto format(my_type my, format_context &ctx) -> decltype(ctx.out())
     {
-        return format_to(ctx.out(), "[my_type i={}]", my.i);
+        return fmt::format_to(ctx.out(), "[my_type i={}]", my.i);
     }
 };
 

include/spdlog/common.h

@@ -132,10 +132,15 @@ using log_clock = std::chrono::system_clock;
 using sink_ptr = std::shared_ptr<sinks::sink>;
 using sinks_init_list = std::initializer_list<sink_ptr>;
 using err_handler = std::function<void(const std::string &err_msg)>;
+#ifdef SPDLOG_USE_STD_STRING_VIEW
+using string_view_t = std::string_view;
+#else
+using string_view_t = fmt::basic_string_view<char>;
+#endif 
+
 #ifdef SPDLOG_USE_STD_FORMAT
 namespace fmt_lib = std;
 
-using string_view_t = std::string_view;
 using memory_buf_t = std::string;
 
 template<typename... Args>
@@ -164,7 +169,6 @@ using wformat_string_t = std::wstring_view;
 #else // use fmt lib instead of std::format
 namespace fmt_lib = fmt;
 
-using string_view_t = fmt::basic_string_view<char>;
 using memory_buf_t = fmt::basic_memory_buffer<char, 250>;
 
 template<typename... Args>
@@ -360,7 +364,7 @@ SPDLOG_CONSTEXPR_FUNC spdlog::wstring_view_t to_string_view(spdlog::wstring_view
 }
 #endif
 
-#ifndef SPDLOG_USE_STD_FORMAT
+#if !defined(SPDLOG_USE_STD_STRING_VIEW) && !defined(SPDLOG_USE_STD_FORMAT)
 template<typename T, typename... Args>
 inline fmt::basic_string_view<T> to_string_view(fmt::basic_format_string<T, Args...> fmt)
 {
@@ -372,6 +376,13 @@ SPDLOG_CONSTEXPR_FUNC std::basic_string_view<T> to_string_view(std::basic_format
 {
     return fmt.get();
 }
+#elif defined(SPDLOG_USE_STD_STRING_VIEW) && !defined(SPDLOG_USE_STD_FORMAT)
+template<typename T, typename... Args>
+SPDLOG_CONSTEXPR_FUNC std::basic_string_view<T> to_string_view(fmt::basic_format_string<T, Args...> fmt) SPDLOG_NOEXCEPT
+{
+    auto tmp = fmt::basic_string_view<T>{fmt};
+    return std::string_view{tmp.data(), tmp.size()};
+}
 #endif
 
 // make_unique support for pre c++14

include/spdlog/details/log_msg_buffer-inl.h

@@ -13,16 +13,16 @@ namespace details {
 SPDLOG_INLINE log_msg_buffer::log_msg_buffer(const log_msg &orig_msg)
     : log_msg{orig_msg}
 {
-    buffer.append(logger_name.begin(), logger_name.end());
-    buffer.append(payload.begin(), payload.end());
+    buffer.append(logger_name.data(), logger_name.data() + logger_name.size());
+    buffer.append(payload.data(), payload.data() + payload.size());
     update_string_views();
 }
 
 SPDLOG_INLINE log_msg_buffer::log_msg_buffer(const log_msg_buffer &other)
     : log_msg{other}
 {
-    buffer.append(logger_name.begin(), logger_name.end());
-    buffer.append(payload.begin(), payload.end());
+    buffer.append(logger_name.data(), logger_name.data() + logger_name.size());
+    buffer.append(payload.data(), payload.data() + payload.size());
     update_string_views();
 }