Overloading operators in C++ basic blueprint.

operatoroverloading.cpp

String & operator += (const String & other) {
        int newlen = _len + other._len; // calc new length
        char * newstr = new char[newlen + 1]; // alloc new buffer
        strcpy(newstr, _s); // copy own contents
        strcpy(newstr + _len, other._s); // append new contents
        delete[] _s; // release orig memory
        _s = newstr; // install new buffer
        return *this;
}

String operator + (const String & s1,
        const String & s2) {
        String result(s1); // clone s1 using copy ctor
        result += s2; // append s2
        return result; // return new result
}

// + for different types
String operator + (const String & s1,
        const char * s2) {
        String result(s1); // clone s1 using copy ctor
        result += String(s2); // append String converted s2
        return result; // return new result
}

bool operator == (const String & s1,
        const String & s2) {
        return (strcmp(s1.data(), s2.data()) == 0);
}

bool operator != (const String & s1,
        const String & s2) {
        return (strcmp(s1.data(), s2.data()) != 0);
}

char & String::operator[](int i) {
        // check for range
        // non-const version allows string[n] to be used as lvalue
        return _s[i];
}

const char & String::operator[](int i) const {
        // check for range here
        // const version allows access to const objects
        return _s[i];
}