How to handle a map with pointers?

Question

Consider I have a class names People. I'm storing pointers to these people in a map

map<string, People*> myMap;

To create new People I use the maps [] operator.

myMap["dave"]->sayHello();

But this gives me a segmentation errors and it doesn't even call the constructor of the People class.

I also tried

 myMap.insert( std::make_pair( "dave", new People() ));

But that didn't change anything, the Constructor still isn't called and the program shuts down processing this code with an segmentation error.

How do I access and manipulate a map with pointers in them? Why isn't the above working, I get no compile time errors or warnings.

Any insight much appreciated, thank you

Answer 1

Given the map:

map<string, People*> myMap;

operator[] won't create new People, it will be creating People*, i.e. pointers that don't point to anything.

The simplest solution is to make your map really contain people, not pointers, e.g.:

map<string, People> myMap;

then the memory management is all handled for you, using operator[] will construct new people as needed.

Answer 2

Try

myMap["dave"] = new People(....);

The new will call the constructor, return a pointer and insert it into the map.

You need to be careful of memory leaks though. Use smart pointers to over come this problem.