Add custom format strings to pattern_formatter

example/example.cpp

@@ -55,6 +55,10 @@ int main(int, char*[])
         spd::set_pattern("*** [%H:%M:%S %z] [thread %t] %v ***");
         file_logger->info("This is another message with custom format");
 
+        auto formatter = std::make_shared<spd::pattern_formatter>("%k: %v");
+        formatter->add_customer_formatter('k', [](spd::details::log_msg &msg){ msg.formatted << "Channel 1"; });
+        file_logger->set_formatter(formatter);
+        file_logger->info("This is another message with another custom format using a custom flag");
 
         // Compile time debug or trace macros.
         // Enabled #ifdef SPDLOG_DEBUG_ON or #ifdef SPDLOG_TRACE_ON

include/spdlog/details/pattern_formatter_impl.h

@@ -377,6 +377,18 @@ private:
     char _ch;
 };
 
+class flag_custom_formatter : public flag_formatter
+{
+private:
+    custom_flag_formatter _formatter;
+public:
+    explicit flag_custom_formatter(custom_flag_formatter formatter) : _formatter(formatter) { };
+    void format(details::log_msg& msg, const std::tm&) override
+    {
+        _formatter(msg);
+    }
+};
+
 
 //aggregate user chars to display as is
 class aggregate_formatter :public flag_formatter
@@ -448,7 +460,7 @@ class full_formatter :public flag_formatter
 ///////////////////////////////////////////////////////////////////////////////
 // pattern_formatter inline impl
 ///////////////////////////////////////////////////////////////////////////////
-inline spdlog::pattern_formatter::pattern_formatter(const std::string& pattern)
+inline spdlog::pattern_formatter::pattern_formatter(const std::string& pattern) : _pattern(pattern)
 {
     compile_pattern(pattern);
 }
@@ -457,6 +469,7 @@ inline void spdlog::pattern_formatter::compile_pattern(const std::string& patter
 {
     auto end = pattern.end();
     std::unique_ptr<details::aggregate_formatter> user_chars;
+    _formatters.clear();
     for (auto it = pattern.begin(); it != end; ++it)
     {
         if (*it == '%')
@@ -480,8 +493,8 @@ inline void spdlog::pattern_formatter::compile_pattern(const std::string& patter
     {
         _formatters.push_back(std::move(user_chars));
     }
-
 }
+
 inline void spdlog::pattern_formatter::handle_flag(char flag)
 {
     switch (flag)
@@ -602,12 +615,61 @@ inline void spdlog::pattern_formatter::handle_flag(char flag)
         break;
 
     default: //Unkown flag appears as is
-        _formatters.push_back(std::unique_ptr<details::flag_formatter>(new details::ch_formatter('%')));
-        _formatters.push_back(std::unique_ptr<details::flag_formatter>(new details::ch_formatter(flag)));
+        auto it = _custom_formatters.find(flag);
+        if(it == _custom_formatters.end())
+        {
+            _formatters.push_back(std::unique_ptr<details::flag_formatter>(new details::ch_formatter('%')));
+            _formatters.push_back(std::unique_ptr<details::flag_formatter>(new details::ch_formatter(flag)));
+        }
+        else
+        {
+            _formatters.push_back(std::unique_ptr<details::flag_formatter>(new details::flag_custom_formatter(it->second)));
+        }
         break;
     }
 }
 
+inline void spdlog::pattern_formatter::add_customer_formatter(char flag, custom_flag_formatter formatter)
+{
+    switch (flag)
+    {//these flags are already in use.
+    case('a') :
+    case('A') :
+    case('b') :
+    case('B') :
+    case('c') :
+    case('C') :
+    case('d') :
+    case('D') :
+    case('e') :
+    case('f') :
+    case('F') :
+    case('h') :
+    case('H') :
+    case('I') :
+    case('n'):
+    case('l'):
+    case('L'):
+    case('m') :
+    case('M') :
+    case('p') :
+    case('r') :
+    case('R') :
+    case('S') :
+    case('t') :
+    case('T') :
+    case('v') :
+    case('x') :
+    case('X') :
+    case('Y') :
+    case('z') :
+    case ('+'):
+       throw spdlog::spdlog_ex(std::string("Can't add custom pattern formatter with non unique signature"));
+    default: //Unkown flag appears as is
+        _custom_formatters.emplace(flag, formatter);
+        compile_pattern(_pattern);
+    }
+}
 
 inline void spdlog::pattern_formatter::format(details::log_msg& msg)
 {

include/spdlog/formatter.h

@@ -10,6 +10,8 @@
 #include <vector>
 #include <string>
 #include <memory>
+#include <unordered_map>
+#include <functional>
 
 namespace spdlog
 {
@@ -25,16 +27,20 @@ public:
     virtual void format(details::log_msg& msg) = 0;
 };
 
+typedef std::function<void(details::log_msg& msg)> custom_flag_formatter;
+
 class pattern_formatter : public formatter
 {
-
 public:
     explicit pattern_formatter(const std::string& pattern);
     pattern_formatter(const pattern_formatter&) = delete;
     pattern_formatter& operator=(const pattern_formatter&) = delete;
     void format(details::log_msg& msg) override;
+    void add_customer_formatter(char sig, custom_flag_formatter formatter);
+
 private:
     const std::string _pattern;
+    std::unordered_map<char, custom_flag_formatter> _custom_formatters;
     std::vector<std::unique_ptr<details::flag_formatter>> _formatters;
     void handle_flag(char flag);
     void compile_pattern(const std::string& pattern);