depend.h

来自「Think in C++文中代码实现」· C头文件 代码 · 共 70 行

// File from page 358 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).
//////////////////////////////////////////////////

//: DEPEND.H -- Static initialization technique
#ifndef DEPEND_H_
#define DEPEND_H_
#include <iostream.h>
extern int x; // Delarations, not definitions
extern int y;

class initializer {
  static int init_count;
public:
  initializer() {
    cout << "initializer()" << endl;
    // Initialize first time only
    if(init_count++ == 0) {
      cout << "performing initialization"
           << endl;
      x = 100;
      y = 200;
    }
  }
  ~initializer() {
    cout << "~initializer()" << endl;
    // Clean up last time only
    if(--init_count == 0) {
      cout << "performing cleanup" << endl;
      // Any necessary cleanup here
    }
  }
};

// The following creates one object in each
// file where DEPEND.H is included, but that
// object is only visible within that file:
static initializer init;

#endif // DEPEND_H_