从用户定义类型到int的词法转换

Question

I am trying to use boost::lexical_cast to convert my user defined type into an integer. However, I get an exception. What am I missing??

class Employee {
private:
    string name;
    int empID;

public:
    Employee() : name(""), empID(-1)
    { }

    friend ostream& operator << (ostream& os, const Employee& e) {
        os << e.empID << endl;      
        return os;
    }
    /*
    operator int() {
        return empID;
    }*/
};

int main() {
    Employee e1("Rajat", 148);
    int eIDInteger = boost::lexical_cast<int>(e1); // I am expecting 148 here.
    return 0;
}

I know I can always use the conversion operator, but just wondering why lexical cast doesn't work here.

Answer 1

The problem is that what you insert into the output stream is not the representation of an integer (because of the trailing << std::endl ). The following fails in a similar way:

boost::lexical_cast<int>("148\n")

Removing the << std::endl makes it work:

friend std::ostream& operator << (std::ostream& os, const Employee& e) {
    os << e.empID;
//  ^^^^^^^^^^^^^^
//  Without << std::endl;

    return os;
}