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REINTERP.CPP
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1995-02-23
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// File from page 753 in "Thinking in C++" by Bruce Eckel
//////////////////////////////////////////////////
// From the compressed package ECKELT01.ZIP 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: eckel@aol.com (please use the same
// address for non-code errors found in the book).
//////////////////////////////////////////////////
//: REINTERP.CPP -- Reinterpret_cast
// Example depends on VPTR location,
// Which may differ between compilers.
#include <string.h>
#include <fstream.h>
ofstream out("reinterp.out");
class X {
enum { sz = 5 };
int a[sz];
public:
X() { memset(a, 0, sz * sizeof(int)); }
virtual void f() {}
// Size of all the data members:
int membsize() { return sizeof(a); }
friend ostream&
operator<<(ostream& os, const X& x) {
for(int i = 0; i < sz; i++)
os << x.a[i] << ' ';
return os;
}
};
main() {
X x;
out << x << endl; // Initialized to zeroes
int* xp = reinterpret_cast<int*>(&x);
xp[1] = 47;
out << x << endl; // Oops!
X x2;
const vptr_size = sizeof(X) - x2.membsize();
long l = reinterpret_cast<long>(&x2);
// *IF* the VPTR is first in the object:
l += vptr_size; // Move past VPTR
xp = reinterpret_cast<int*>(l);
xp[1] = 47;
out << x2 << endl;
}