STL Map - Displaying what is pointed to by find() function - c++

Question

For testing purposes, I'm running the following code through a for loop. Only the first three keys actually exist, and "Record found" is displayed as expected, along with the key, retrieved from findVertex->first.
My question is, how would I be able to access the second value being pointed to?
findVertex->secondseems obvious, but does not work, as the second value is an object I created, the declaration of which is given below the code, if it would be of any use.
for(int i = 0; i<10; i++)
{
map<int, vector<Vertex> >::const_iterator findVertex = vertexMap.find(i);
if(findVertex != vertexMap.end())
{
cout<<"\nRecord found: ";
cout<<findVertex->first;
cout<<findVertex->second; //does not work
}
else
cout<<"\nRecord not found";
}
Class code:
class Vertex
{
private:
int currentIndex;
double xPoint, yPoint, zPoint;
vector<double> attributes;
public:
friend istream& operator>>(istream&, Vertex &);
friend ostream& operator<<(ostream&, Vertex &);
};
Thanks

Answer 1

Your map is of the type
map<int, vector<Vertex>>
This means first is an int, and second is vector<Vertex>.
While you have defined operator<< for Vertex, there is no such function for vector<Vertex>. You'd have iterate through your vector, if you have access to C++11 you can use something like
if(findVertex != vertexMap.end())
{
cout << "\nRecord found: ";
cout << findVertex->first << '\n';
for (auto const& vertex : findVertex->second)
{
cout << vertex << '\n';
}
}
If you don't have access to C++11 you can do the same idea manually
if(findVertex != vertexMap.end())
{
cout << "\nRecord found: ";
cout << findVertex->first << '\n';
for (vector<Vertex>::const_iterator itVertex = findVertex->second.cbegin();
itVertex != findVertex->second.cend();
++itVertex)
{
Vertex const& vertex = *itVertex;
cout << vertex << '\n';
}
}

Answer 2

First of all you may not use const_iterator
map<int, vector<Vertex> >::const_iterator findVertex = vertexMap.find(i);
to display Vertex because you declared operator << with second parameter as a non-const reference
friend ostream& operator<<(ostream&, Vertex &);
^^^^^^^^
You should declare it like
friend ostream& operator<<(ostream&, const Vertex &);
^^^^^
Otherwise change the above statement to the following
map<int, vector<Vertex> >::iterator findVertex = vertexMap.find(i);
^^^^^^^^
And change this statement
cout<<findVertex->second; //does not work
to the following code snippet
for ( Vertex &v : findVertex->second ) cout << v << endl;
If you will modify the operator specyfying qualifier const for the second parameter then you can write
map<int, vector<Vertex> >::const_iterator findVertex = vertexMap.find(i);
^^^^^^^^^^^^^^
//...
for ( const Vertex &v : findVertex->second ) cout << v << endl;
^^^^^
Or instead of the range based for statement you can use an ordinary loop as for example
for ( std::vector<Vertex>::size_type i = 0; i < findVertex->second.size(); i++ )
{
std::cout << findVertex->second[i] << std::endl;
}
or
for ( std::vector<Vertex>::iterator it = findVertex->second.begin();
it != findVertex->second.end();
++it )
{
std::cout << *it << std::endl;
}