mem.cpp

ThinkingC++中文版

//: C07:Mem.cpp {O}
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
#include "Mem.h"
#include <cstring>

Mem::Mem() 	//The default constructor doesn’t allocate any storage
{ 
	mem = 0; size = 0; }

Mem::Mem(int sz)   //the second constructor ensures that there is sz storage in the Mem object.
{
	mem = 0;
	size = 0;
	ensureMinSize(sz); 
}

//当两个函数利用缺省参数合二为一时，代码不需要修改，这种情况适宜使用缺省参数
/*
 Mem::Mem(int sz)
 {
	mem = 0;
	size = 0;
	ensureMinSize(sz); 

 }

*/

Mem::~Mem()  //The destructor releases the storage, 
{ 
	delete []mem; }

int Mem::msize() //tells you how many bytes there are currently in the Mem object,
{ 
	return size; }

void Mem::ensureMinSize(int minSize) //to increase the size of the memory block 
{
  if(size < minSize) {
    byte* newmem = new byte[minSize];
    memset(newmem + size, 0, minSize - size);  	//the first argument Pointer to destination,the second argument is Character to set,the third argument is Number of characters to be set.
    memcpy(newmem, mem, size);
    delete []mem;
    mem = newmem;
    size = minSize;
  }
}

byte* Mem::pointer()  //produces a pointer to the starting address of the storage 
{ 
	return mem; }

byte* Mem::pointer(int minSize) //to want a pointer to a block of bytes that is at least minSize large,
{
  ensureMinSize(minSize);
  return mem; 
} ///:~