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c++staticstdmap

Static map initialization

I have the following code:

//MyClass.h
class MyClass {
public:
    typedef std::map<std::string, int> OpMap;
    static OpMap opMap_;     
    // (more methods)
};

//MyClass.cpp
//Init opMap_
MyClass::opMap_["x"] = 1; //compilation error

How can I (statically) initialize opMap_?

Solution

  • If you're using C++11, you could use initializer lists:

    //MyClass.h
class MyClass {
public:
      typedef std::map<std::string, int> OpMap;
      static OpMap opMap_;
};

//MyClass.cpp
MyClass::OpMap MyClass::opMap_ = { 
    { "x", 1 }
};

    If you don't have access to a compiler that supports the C++11 standard, you could do the following:

    //MyClass.h
class MyClass {
public:
      typedef std::map<std::string, int> OpMap;
      static OpMap opMap_;
private:
      static OpMap init_map() {
          OpMap some_map;
          some_map["x"] = 1;
          return some_map;
      }
};

//MyClass.cpp
MyClass::OpMap MyClass::opMap_ = init_map();