How to convert wstring into string?

The question is how to convert wstring to string?

I have next example :

#include <string>
#include <iostream>

int main()
{
    std::wstring ws = L"Hello";
    std::string s( ws.begin(), ws.end() );

  //std::cout <<"std::string =     "<<s<<std::endl;
    std::wcout<<"std::wstring =    "<<ws<<std::endl;
    std::cout <<"std::string =     "<<s<<std::endl;
}

the output with commented out line is :

std::string =     Hello
std::wstring =    Hello
std::string =     Hello

but without is only :

std::wstring =    Hello

Is anything wrong in the example? Can I do the conversion like above?

EDIT

New example (taking into account some answers) is

#include <string>
#include <iostream>
#include <sstream>
#include <locale>

int main()
{
    setlocale(LC_CTYPE, "");

    const std::wstring ws = L"Hello";
    const std::string s( ws.begin(), ws.end() );

    std::cout<<"std::string =     "<<s<<std::endl;
    std::wcout<<"std::wstring =    "<<ws<<std::endl;

    std::stringstream ss;
    ss << ws.c_str();
    std::cout<<"std::stringstream =     "<<ss.str()<<std::endl;
}

The output is :

std::string =     Hello
std::wstring =    Hello
std::stringstream =     0x860283c

therefore the stringstream can not be used to convert wstring into string.