std::unordered_map undeclared identifier using Visual C++ 2008

Question

#include <iostream>
#include <string>
#include <unordered_map>

using namespace std;

int main()
{
    unordered_map< int, string > m;

    m[1] = "one";   
    m[2] = "two";
    m[4] = "four";
    m[3] = "three";
    m[2] = "TWO!";
    cout << m[2] << endl;

    m.clear();
    return 0;
}

I am learning and can't figure it out. The compiler throws the error that type unordered_map is undeclared.

I am using Visual C++ 2008 Express Edition.

Answer 1

In Visual Studio 2008 the classes in Technical Report 1 (TR1) are in namespace std::tr1. Add:

using namespace std::tr1;

to your code.

Answer 2

In the TR1 unordered_map is available from the <tr1/unordered_map> header file as std::tr1::unordered_map.

In the upcoming C++0x standard it is available from the <unordered_map> header file as std::unordered_map.

so you should use <tr1/unordered_map> header and std::tr1::unordered_map namespace for vc 2008 because vc 2008 does not support C++0x.

To answer the problem you quoted in comment.
Also, Make sure you download the feature pack for VS2008!

Check under new features supported list.

New containers (tuple, array, unordered set, etc)