C++類中靜態數據成員MAP如何初始化

conv_xxx.hpp

class convolution 
{
       ...
       ...
        typedef std::map<int, std::string> ConvDtMap;
        
        static ConvDtMap conv_dt_map;

        static   ConvDtMap CreateDtMap()
        {
            ConvDtMap tmp_map;
            tmp_map.insert(std::pair<int, std::string>(0, "INVALID"));
            return tmp_map;
        }
}                

convolution::ConvDtMap  convolution::conv_dt_map = convolution::CreateDtMap);