Question

I have a map<string, string> and I need to fill it with default pairs on construction. like "Sam" : "good", "ram" : "bad". How in C++03 to do it most readably in code terms on construction?

Answer 1

boost::assign::map_list_of lets you do this with some pretty looking syntax, but if you can’t use Boost, you could write your own.

#include <map>
#include <string>

template< class Key, class Type, class Traits = std::less<Key>,
          class Allocator = std::allocator< std::pair <const Key, Type> > >
class MapInit
{
  std::map<Key, Type, Traits, Allocator> myMap_;

  /* Disallow default construction */
  MapInit();

public:
  typedef MapInit<Key, Type, Traits, Allocator> self_type;
  typedef typename std::map<Key, Type, Traits, Allocator>::value_type value_type;

  MapInit( const Key& key, const Type& value )
  {
    myMap_[key] = value;
  }


  self_type& operator()( const Key& key, const Type& value )
  {
    myMap_[key] = value;
    return *this;
  }


  operator std::map<Key, Type, Traits, Allocator>()
  {
    return myMap_;
  }
};

int main()
{
  std::map<int, std::string> myMap = 
    MapInit<int, std::string>(10, "ten")
                             (20, "twenty")
                             (30, "thirty");
}