statcast.cpp

Think in C++文中代码实现

// File from page 749 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 
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// 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).
//////////////////////////////////////////////////

//: STATCAST.CPP -- Examples of static_cast

class base { /* ... */ };
class derived : public base {
public:
  // ...
  // Automatic type conversion:
  operator int() { return 1; }
};

void func(int) {}

class other {};

main() {
  int i = 0x7fff; // Max pos value = 32767
  long l;
  float f;
  //(1) typical castless conversions:
  l = i;
  f = i;
  // Also works:
  l = static_cast<long>(i);
  f = static_cast<float>(i);

  //(2) narrowing conversions:
  i = l; // May lose digits
  i = f; // May lose info
  // Says "I know," eliminates warnings:
  i = static_cast<int>(l);
  i = static_cast<int>(f);
  char c = static_cast<char>(i);

  //(3) forcing a conversion from void* :
  void* vp = &i;
  // Old way produces a dangerous conversion:
  float* fp = (float*)vp;
  // The new way is equally dangerous:
  fp = static_cast<float*>(vp);

  //(4) implicit type conversions, normally
  // Performed by the compiler:
  derived d;
  base* bp = &d; // Upcast: normal and OK
  bp = static_cast<base*>(&d); // More explicit
  int x = d; // Automatic type conversion
  x = static_cast<int>(d); // More explicit
  func(d); // Automatic type conversion
  func(static_cast<int>(d)); // More explicit

  //(5) Static Navigation of class hierarchies:
  derived* dp = static_cast<derived*>(bp);
  // ONLY an efficiency hack. dynamic_cast is
  // Always safer. However:
  // Other* op = static_cast<other*>(bp);
  // Conveniently gives an error message, while
  other* op2 = (other*)bp;
  // Does not.
}