unary.cpp

来自「Think in C++文中代码实现」· C++ 代码 · 共 196 行

// File from page 401 in "Thinking in C++" by Bruce Eckel
//////////////////////////////////////////////////
// From the compressed package ECKELT02.ZIP 4/11/95
// (Original ECKELT01.ZIP dated 2/21/95)
// Copyright (c) Bruce Eckel, 1995 
// Source code file from the book "Thinking in C++", 
// Prentice Hall, 1995, ISBN: 0-13-917709-4
// All rights reserved EXCEPT as allowed by the following 
// statements: You may freely use this file for your own 
// work, including modifications and distribution in 
// executable form only. You may copy and distribute this 
// file, as long as it is only distributed in the complete 
// (compressed) package with the other files from this 
// book and you do not remove this copyright and notice. 
// You may not distribute modified versions of the source 
// code in this package. This package may be freely placed 
// on bulletin boards, internet nodes, shareware disks and 
// product vendor disks. You may not use this file in 
// printed media without the express permission of the 
// author. Bruce Eckel makes no 
// representation about the suitability of this software 
// for any purpose. It is provided "as is" without express 
// or implied warranty of any kind. The entire risk as to 
// the quality and performance of the software is with 
// you. Should the software prove defective, you assume 
// the cost of all necessary servicing, repair, or 
// correction. 
// If you think you've found an error, please 
// email all modified files with loudly commented changes 
// to: [e-mail] (please use the same 
// address for non-code errors found in the book).
//////////////////////////////////////////////////

//: UNARY.CPP -- Overloading unary operators
#include <iostream.h>
class integer {
  long i;
  integer* This() { return this; }
public:
  integer(long I = 0) : i(I) {}
  // 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 integer*
    operator&(integer& a);
  friend int
    operator!(const integer& a);
  // Side effects don't take 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\n";
  return a; // Unary + has no effect
}
const integer operator-(const integer& a) {
  cout << "-integer\n";
  return integer(-a.i);
}
const integer operator~(const integer& a) {
  cout << "~integer\n";
  return integer(~a.i);
}
integer* operator&(integer& a) {
  cout << "&integer\n";
  return a.This(); // &a is recursive!
}
int operator!(const integer& a) {
  cout << "!integer\n";
  return !a.i;
}
// Prefix; return incremented value
const integer& operator++(integer& a) {
  cout << "++integer\n";
  a.i++;
  return a;
}
// Postfix; return the value before increment:
const integer operator++(integer& a, int) {
  cout << "integer++\n";
  integer r(a.i);
  a.i++;
  return r;
}
// Prefix; return decremented value
const integer& operator--(integer& a) {
  cout << "--integer\n";
  a.i--;
  return a;
}
// Postfix; return the value before decrement:
const integer operator--(integer& a, int) {
  cout << "integer--\n";
  integer r(a.i);
  a.i--;
  return r;
}

void f(integer a) {
  +a;
  -a;
  ~a;
  integer* ip = &a;
  !a;
  ++a;
  a++;
  --a;
  a--;
}

// Member operators (implicit "this"):
class byte {
  unsigned char b;
public:
  byte(unsigned char B = 0) : b(B) {}
  // No side effects: const member function:
  const byte& operator+() const {
    cout << "+byte\n";
    return *this;
  }
  const byte operator-() const {
    cout << "-byte\n";
    return byte(-b);
  }
  const byte operator~() const {
    cout << "~byte\n";
    return byte(~b);
  }
  byte operator!() const {
    cout << "!byte\n";
    return byte(!b);
  }
  byte* operator&() {
    cout << "&byte\n";
    return this;
  }
  // Side effects: non-const member function:
  const byte& operator++() { // Prefix
    cout << "++byte\n";
    b++;
    return *this;
  }
  const byte operator++(int) { // Postfix
    cout << "byte++\n";
    byte before(b);
    b++;
    return before;
  }
  const byte& operator--() { // Prefix
    cout << "--byte\n";
    --b;
    return *this;
  }
  const byte operator--(int) { // Postfix
    cout << "byte--\n";
    byte before(b);
    --b;
    return before;
  }
};

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

main() {
  integer a;
  f(a);
  byte b;
  g(b);
}