lexical cast c++

how can we write a wrapper lexical cast function in order to implement lines like :

int value = lexical_cast<int> (string)

I am quite new to programming and was wondering how we can write the function. I don't know how to figure out a template. Also can we write a wrapper function for double too ? Like

double value = lexical_cast2<double> (string)

??

To have it as you stated in your example:

#include <sstream>

template <class Dest>
class lexical_cast
{
    Dest value;
public:
    template <class Src>
    lexical_cast(const Src &src) {
        std::stringstream s;
        s << src;
        s >> value;
    }

    operator const Dest &() const {
        return value;
    }

    operator Dest &() {
        return value;
    }
};

Including error checking:

    template <class Src>
    lexical_cast(const Src &src) throw (const char*) {
        std::stringstream s;
        if (!(s << src) || !(s >> value) || s.rdbuf()->in_avail()) {
            throw "value error";
        }
    }