Question

I am having trouble accessing data inside a map using an iterator. I want to return all of the values inserted into the map by using an iterator. However, when I use the iterator, it doesn’t acknowledge any of the members in the instance of the class it has been past into.

int main()
{
    ifstream inputFile;
    int numberOfVertices;
    char filename[30];
    string tmp;

    //the class the holds the graph
    map<string, MapVertex*> mapGraph;

    //input the filename
    cout << "Input the filename of the graph: ";
    cin >> filename;
    inputFile.open(filename);

    if (inputFile.good())
    {
        inputFile >> numberOfVertices;
        inputFile.ignore();

        for (int count = 0; count < numberOfVertices; count++)
        {
            getline(inputFile, tmp);
            cout << "COUNT: " << count << "  VALUE: " << tmp << endl;

            MapVertex tmpVert;
            tmpVert.setText(tmp);
            mapGraph[tmp]=&tmpVert;
        }

        string a;
        string connectTo[2];

        while (!inputFile.eof())
        {

            //connectTo[0] and connectTo[1] are two strings that are behaving as keys

            MapVertex* pointTo;
            pointTo = mapGraph[connectTo[0]];
            pointTo->addNeighbor(mapGraph[connectTo[1]]);
            //map.find(connectTo[0]).addNeighbor(map.find(connectTo[1]));
            //cout << connectTo[0] << "," << connectTo[1] << endl;
        }

        map<string,MapVertex*>::iterator it;
        for (it=mapGraph.begin(); it!=mapGraph.end(); it++)
        {
            cout << it->getText() << endl;

        }
    }

    return 0;
}

Compiler output:

\lab12\main.cpp||In function `int main()':|
\lab12\main.cpp|69|error: 'struct std::pair<const std::string, MapVertex*>'
                           has no member named 'getText'|
||=== Build finished: 1 errors, 0 warnings ===|

There is an access member in my MapVertex class called getText() which returns the data that is inside it.

Answer 1

To fix the compiler error, you need to do it->second->getText() as the *iterator is a pair<string, MapVertex*>. But there are other problems in your code. While inserting into the map, you are inserting the address of a local variable into it. This address will be invalid by the time you try to iterate the map using for loop. I would suggest you to declare the map as std::map<string, MyVertex> so that when you insert into the map a copy of the MyVertex is inserted into map.