howmany.cpp

Think in C++文中代码实现

// File from page 376 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).
//////////////////////////////////////////////////

//: HOWMANY.CPP -- Class counts its objects
#include <fstream.h>
ofstream out("howmany.out");

class howmany {
  static int object_count;
public:
  howmany() {
    object_count++;
  }
  static void print(const char* msg = 0) {
    if(msg) out << msg << ": ";
    out << "object_count = "
         << object_count << endl;
  }
  ~howmany() {
    object_count--;
    print("~howmany()");
  }
};

int howmany::object_count = 0;

// Pass and return BY VALUE:
howmany f(howmany x) {
  x.print("x argument inside f()");
  return x;
}

main() {
  howmany h;
  howmany::print("after construction of h");
  howmany h2 = f(h);
  howmany::print("after call to f()");
}