14.3.1.1 Defining Your Own Insertion Operator

The following example defines a string class:

#include <stdlib.h>
#include <iostream.h>


class string {
private:
    char* data;
    size_t size;

public:
    // (functions not relevant here)

    friend ostream& operator<<(ostream&, const string&);
    friend istream& operator>>(istream&, string&);
};

The insertion and extraction operators must in this case be defined as friends because the data part of the string class is private.

ostream& operator<< (ostream& ostr, const string& output)
{    return ostr << output.data;}

Here is the definition of operator<< overloaded for use with strings.

cout << string1 << string2;

operator<< takes ostream& (that is, a reference to an ostream) as its first argument and returns the same ostream, making it possible to combine insertions in one statement.