运算符重载 C++ 编程思想

class Integer{
    int i;
public:
    Integer(int ii) : i(ii) {}
    const Integer operator+(const Integer& rv) const {
        cout << "operator+" << endl;
        return Integer(i + rv.i);
    }
    Integer& operator+=(const Integer& rv) {
        cout << "operator+=" << endl;
        i += rv.i;
        return *this;
    }
};

int main() {
    cout << "build-in types:" << endl;
    int i = 1, j = 2, k = 3;
    k += i + j;
    cout << "user-defined types:" << endl;
    Integer ii(1), jj(2), kk(3);
    kk += ii + jj;
}

//: C12:OverloadingUnaryOperators.cpp
#include <iostream>
using namespace std;

// Non-member functions:
class Integer {
    long i;
    Integer* This() { return this;}
    
public:
    Integer(long ll = 0) : i(ll) {}
    //No side effects takes const& argument:
    friend const Integer& operator+(const Integer& a);
    friend const Integer operator-(const Integer& a);
    friend const Integer operator~(const Integer& a);
    friend const Integer* operator&(Interger& a);
    friend const int operator!(const Integer& a);
    //Side effects have non-const& argument:
    //Prefix:
    friend const Integer& operator++(Integer& a);
    //Postfix:
    friend const Integer operator++(Integer& a, int);
    //Prefix:
    friend const Integer& operator--(Integer& a);
    //Postfix:
    friend const Integer operator--(Integer& a, int);
};

//Global operators:
const Integer& operator+(const Integer& a) {
    cout << "+Integer
";
    return a; //Unary + has no effect
}
const Integer operator-(const Integer& a) {
    cout << "-Integer
";
    return Integer(-a.i);
}
const Integer operator~(const Integer& a) {
    cout << "~Integer
";
    return Integer(~a.i);
}
Integer* operator(Integer& a) {
    cout << "&Integer
";
    return a.This();
}
int operator!(const Integer& a) {
    cout << "!Integer
";
    return !a.i;
}
//Prefix; return incremented value
const Integer& operator++(Integer& a) {
    cout << "++Integer
";
    a.i ++;
    return a;
}
//Postfix; return the value before increment:
const Integer operator++(Integer& a, int) {
    cout << "Integer++
";
    Integer before(a.i);
    a.i ++;
    return before;
}
//Prefix; return decremented value
const Integer& operator--(Integer& a) {
    cout << "--Integer
";
    a.i --;
    return a;
}
//Postfix; return the value before decrement:
const Integer operator--(Integer& a, int) {
    cout << "Integer--
";
    Integer before(a.i);
    a.i --;
    return before;
}

//Show that the overloaded operators work:
void f(Integer a) {
    +a;
    -a;
    ~a;
    Integer *ip = &a;
    !a;
    ++a;
    a++;
    --a;
    a--;
}

class Byte {
    unsigned char b;
public:
    Byte(unsigned char bb = 0) : b(bb) {}
    // No side effects: const memeber function:
    const Byte& operator+() const {
        cout << "+Byte
";
        return *this;
    }
    const Byte operator-() const {
        cout << "-Byte
";
        return Byte(-b);
    }
    const Byte operator~() const {
        cout << "~Byte
";
        return Byte(~b);
    }
    Byte operator!() const {
        cout << "!Byte
";
        return Byte(!b);
    }
    Byte* operator&() {
        cout << "&Byte
";
        return this;
    }
    // Side effects: non-const member function:
    const Byte& operator++() { //Prefix
        cout << "++Byte
";
        b ++; 
        return *this;
    }
    const Byte operator++(int) { //Postfix
        cout << "Byte++
";
        Byte before(b);
        b ++;
        return before;
    }
    const Byte& operator--() { //Prefix
        cout << "--Byte
";
        b --;
        return *this;
    }
    const Byte operator--(int) { //Postfix
        cout << "Byte--
";
        Byte before(b);
        b --;
        return before;
    }
};

void g(Byte b) {
    +b;
    -b;
    ~b;
    Byte *bp = &b;
    !b;
    ++b;
    b++;
    --b;
    b--;
}

int main() {
    Integer a;
    f(a);
    Byte b;
    g(b);
}