Remove new macro, update example with correct way to specify fmt lib namespace when fmt_lib namespace alias cannot be used.

example/example.cpp

@@ -262,7 +262,14 @@ struct my_type
         : i(i){};
 };
 
-FMTLIB_BEGIN_NAMESPACE
+
+// Using a namespace alias like fmt_lib is not allowed when extending an existing namespace,
+// but the correct namespace can still be selected with the SPDLOG_USE_STD_FORMAT macro.
+#ifdef SPDLOG_USE_STD_FORMAT
+    namespace std {
+#else
+    namespace fmt {
+#endif
 template<>
 struct formatter<my_type> : formatter<std::string>
 {
@@ -271,7 +278,7 @@ struct formatter<my_type> : formatter<std::string>
         return format_to(ctx.out(), "[my_type i={}]", my.i);
     }
 };
-FMTLIB_END_NAMESPACE
+}
 
 void user_defined_example()
 {

include/spdlog/common.h

@@ -126,13 +126,6 @@ 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_FORMAT
-#    ifndef FMTLIB_BEGIN_NAMESPACE
-#        define FMTLIB_BEGIN_NAMESPACE \
-           namespace std {
-#        define FMTLIB_END_NAMESPACE \
-           }
-#    endif
-
 namespace fmt_lib = std;
 
 using string_view_t = std::string_view;
@@ -153,16 +146,7 @@ template<typename... Args>
 using wformat_string_t = std::wstring_view;
 #    endif
 #    define SPDLOG_BUF_TO_STRING(x) x
-
 #else // use fmt lib instead of std::format
-
-#    ifndef FMTLIB_BEGIN_NAMESPACE
-#        define FMTLIB_BEGIN_NAMESPACE \
-           namespace fmt {
-#        define FMTLIB_END_NAMESPACE \
-           }
-#    endif
-
 namespace fmt_lib = fmt;
 
 using string_view_t = fmt::basic_string_view<char>;