C++ new和delete重载
参考文章：http://blog.163.com/hbu_lijian/blog/static/126129153201211510361484/
http://blog.csdn.net/hzyong_c/article/details/5949314
首先，new和delete是运算符，重载new和delete是可能的。这样做的原因是，有时希望使用某种特殊的动态内存分配方法。例如，可能有些分配子程序，他们的堆已耗尽，自动开始把一个磁盘文件当虚存储使用，或者用户希望控制某一片存储空间的分配等。
先看一下重载new/delete的规则：
重载的operator new的参数个数任意，但第一个参数必须是size_t类型的，返回值必须是void*。重载operator delete只允许有一个参数，且是void*型。
void *operator new (size_t size){
.......//完成分配工作
return pointer_to_memory;
}
void operator delete(void *p)
{
......//释放由p指向的存储空间
}
1.局部重载new和delete（可以使用成员函数和友元函数两种方式重载）
使用new分配某个重载了new的累的对象空间时，先调用new的重载函数，再调用该类的构造函数，如果该类的构造函数有参数要求，则必须给出对应的实参。
使用了delete释放某个重载了delete的累的对象空间时，先调用类的析构函数，然后再调用重载的delete函数。
#include <iostream>
#include <stdlib.h>
#include <string.h>
using namespace std;
class three_d
{
private:
int x,y,z;
public:
three_d(int a,int b,int c);
~three_d()
{
cout << "Destructing\n";
}
void *operator new(size_t size);
void operator delete(void *p);
friend ostream & operator <<(ostream &stream,three_d obj);
};
three_d::three_d(int a,int b,int c)
{
cout << "Constructing\n";
x = a;
y = b;
z = c;
}
void *three_d::operator new(size_t size)
{
cout << "in threee_d new\n";
return malloc(size);
}
void three_d::operator delete(void *p)
{
cout << "in three_d delete\n" ;
free(p);
}
ostream &operator <<(ostream &os,three_d obj)
{
os << obj.x << ",";
os << obj.y << ",";
os << obj.z << "\n";
return os;
}
int main(int argc,char *argv[])
{
three_d *p = new three_d(1,2,3);
three_d *p1 = new three_d(4,5,6);
if(!p || !p1)
{
cout << "Allocation failure" << endl;
return 1;
}
cout << *p << *p1;
delete p;
delete p1;
int *pnum;
pnum = new int;
*pnum = 0;
cout << "num = " << *pnum << endl;
delete pnum;
cout << "Application Run Successfully!" << endl;
return 0;
}
2.全局重载new和delete
可以在任何类说明之外重在new和delete，使它们成为全局的。当new和delete被重载为全局时，C++原来的new与delete被忽略，并且重载的运算符用于所有类型（包括标准型和用户定义类型）的分配要求。
#include <iostream>
#include <stdlib.h>
#include <string.h>
using namespace std;
class three_d
{
private:
int x,y,z;
public:
three_d(int a,int b,int c);
~three_d()
{
cout << "Destructing\n";
}
friend ostream & operator <<(ostream &stream,three_d obj);
};
three_d::three_d(int a,int b,int c)
{
cout << "Constructing\n";
x = a;
y = b;
z = c;
}
void *operator new(size_t size)
{
cout << "in threee_d new\n";
return malloc(size);
}
void operator delete(void *p)
{
cout << "in three_d delete\n" ;
free(p);
}
ostream &operator <<(ostream &os,three_d obj)
{
os << obj.x << ",";
os << obj.y << ",";
os << obj.z << "\n";
return os;
}
int main(int argc,char *argv[])
{
three_d *p = new three_d(1,2,3);
three_d *p1 = new three_d(4,5,6);
if(!p || !p1)
{
cout << "Allocation failure" << endl;
return 1;
}
cout << *p << *p1;
delete p;
delete p1;
int *pnum;
pnum = new int;
*pnum = 0;
cout << "num = " << *pnum << endl;
delete pnum;
cout << "Application Run Successfully!" << endl;
return 0;
}
实际应用中可能需要在new中作更多的处理，内存检测等，new重载时也可以加入其他的参数，例如__FILE__、__LINE__等，以便于快速定位问题。