getmem.h

Think in C++文中代码实现

// File from page 633 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).
//////////////////////////////////////////////////

//: GETMEM.H -- Function template for memory
#ifndef GETMEM_H_
#define GETMEM_H_
#include <stdlib.h>
#include <string.h>
#include "..\allege.h"

template<class T>
void getmem(T*& oldmem, int elems) {
  typedef int cntr; // Type of element counter
  const int csz = sizeof(cntr); // And size
  const int Tsz = sizeof(T);
  if(elems == 0) {
    free(&(((cntr*)oldmem)[-1]));
    return;
  }
  T* p = oldmem;
  cntr oldcount = 0;
  if(p) { // Previously allocated memory
    ((cntr*)p)--; // Back up by one cntr
    oldcount = *(cntr*)p; // Previous # elems
  }
  T* m = (T*)realloc(p, elems * Tsz + csz);
  allegemem(m);
  *((cntr*)m) = elems; // Keep track of count
  const cntr increment = elems - oldcount;
  if(increment > 0) {
    // Starting address of data:
    long startadr = (long)&(m[oldcount]);
    startadr += csz;
    // Zero the additional new memory:
    memset((void*)startadr, 0, increment * Tsz);
  }
  // Return the address beyond the count:
  oldmem = (T*)&(((cntr*)m)[1]);
}

template<class T>
inline void freemem(T * m) { getmem(m, 0); }

#endif // GETMEM_H_