C++ STL map with a custom class as second type

Question

Newbie question here.

I'd like to create a map with an int and my own custom class. Is there a way to do this?

map myMap;

If not, how do I go about accomplishing this? Basically, I want an id(or preferably an enum) to point to my own custom class. In most other languages, this would be a simple hash.

Thanks.

Answer 1

#include <map>

std::map<int, MyClass> myMap;

MyClass foo;
myMap[5] = foo;
myMap[5].bar = 10;

You do need MyClass to be default- and copy- constructible, so it can be created (if you use, e.g., myMap[5]) and copied into the map.

Answer 2

Yes the only condition are:

• The key Type is comparable (Good)
• The value Type is copy constructable ?

So you just need to make sure you are object is copy constructable so that it can be copied into the map.

Answer 3

you should use like this

typedef std::map myMapType;

myMapType myMap;

But be careful when inserting your class in this as if you insert more than one time for same key, you will never get a notice :

Call myMapType::iterator itr myMap.find(key) , depending upon return type and your program requirments you can procced.

Like wise try to avid access any element using [] operator like

 somefunc(myMap[10]);

As you will not get an error from map even there was noting inserted for key 10