对于无法插入到映射中的下列映射
map<string, double> doubleProps = 4;
map<string, int32> intProps = 5;
map<string,string> stringProps=6;
下面是我尝试过的,但是没有用
doubleProps["key"]="value" //doesn't work
*(doubleProps["key"]).insert("value") //doesn't work
doubleProps.insert("key","value")
这是在C++中在protobuf对象中插入映射的方法
(*mutable_stringprops())["key"]=value
https://developers.google.com/protocol-buffers/docs/reference/cpp-generated#map-fields