c++ - How can I switch between std::map or std::unordered_map as a container in a class? -

i have ifdef typedef in class:

#ifdef hashmap     typedef std::unordered_map<unsigned int, l1entry> l1; //c++ 11 #else     typedef std::map<unsigned int, l1entry> l1; #endif 

i need control container used when create new object of class. best approach this?

make container template parameter of class:

template<typename maptype> class myclass { public:     // ...  private:     maptype mymap; }; 

and instantiate so:

myclass< std::map<unsigned int, l1entry> > obj; myclass< std::unordered_map<unsigned int, l1entry> > obj2; 

there's container in standard library this, take @ std::queue default implemented std::deque can specify container, long container provides operations.

here's version have specify std::map or std::unordered_map:

#include <map> #include <unordered_map>  typedef size_t l1entry;  template<template <typename...> class container> class myclass {     typedef container<int, l1entry> maptype; public:     // ...  private:     maptype mymap; };  int main() {     myclass<std::map> obj;     myclass<std::unordered_map> obj2; } 

ok! here's final version, show how can split code in .h/.cpp (everything goes in .h except section marked):

#ifndef mymap_h #define mymap_h  #include <map> #include <unordered_map> #include <iostream>  typedef size_t l1entry;  template<template <typename...> class container> class myclass {     typedef container<int, l1entry> maptype; public:     void printmap();  private:     maptype mymap; };  // start of cpp chunk (replace #include <whatever.h>) template<template <typename...args> class container> void myclass< container >::printmap() {     // ... actual printing     std::cout << "you'd print stuff here." << std::endl; } // end of cpp chunk  #endif // mymap_h 

and main.cpp:

#include "mymap.h"  int main() {     myclass<std::map> obj;     myclass<std::unordered_map> obj2;      obj.printmap();     obj2.printmap();      return 0; }