New的放置语法

来源：互联网发布：2016大数据企业排行榜编辑：程序博客网时间：2024/05/21 15:40

本文章转自网易博客：小萝卜头
http://mmjinglin.blog.163.com/blog/static/20486210201262411360/16
//placenew2.cpp---new,placement new,no delete#include<iostream>#include<string>#include<new>//放置语法中需调用using namespace std;const int BUF=512;
class JustTesting{private: string words; int number; char c1;public: JustTesting(const string & s="Just Testing",int n=0) {words=s;number=n;cout<<words<<" constructed\n";} ~JustTesting(){cout<<words<<" destroyed\n";} void Show() const{cout<<words<<", "<<number<<endl;}};int main(){ char *buffer=new char[BUF];         // get a block of memory
//new操作符创建一个512字节的内存缓冲区 JustTesting *pc1,*pc2;
 pc1=new (buffer) JustTesting;       //place object in buffer pc2=new JustTesting("Heap1",20);    //place object on heap
 cout<<"Memory block addresses:\n"<<"buffer:"  <<(void*)buffer<<",  heap:"<<pc2<<endl; cout<<"Memory contents:\n"; cout<<pc1<<": "; pc1->Show(); cout<<pc2<<": "; pc2->Show();
 JustTesting *pc3,*pc4; //fix placement new location pc3=new (buffer+sizeof(JustTesting)) JustTesting("Better Idea",6);
//自行管理内存缓存区内存单元，为pc1和pc3提供位于缓存区的不同地址 pc4=new JustTesting("Heap2",10);
 cout<<"Memory contents:\n"; cout<<pc3<<": "; pc3->Show(); cout<<pc4<<": "; pc4->Show();
 delete pc2;                //free Heap1 delete pc4;                //free Heap2 //explicitly destory placement new objects pc3->~JustTesting();       //destory object pointed to by pc3 pc1->~JustTesting();       //destory object pointed to by pc4、
//使用指向对象的指针，显示调用析构函数销毁对象 delete [] buffer;    //释放使用常规new操作符分配的整个内存块，但他没有为布局new操作符在该内存块中创建的对象调用析构函数，因此需要显示调用析构函数 cout<<"Done \n";// cout<<sizeof(string); //cout<<sizeof(JustTesting); return 0;}

pc1=new (buffer) JustTesting; 放置语法：就是从buffer为首地址分配一段内存给pc1，这段内存是已经预先开辟的。

delete [] buffer; 使用deletet释放buffer中常规new操作符分配的整个内存块时，没有为布局new操作符在该内存块中创建的对象pc1，pc3调用析构函数，因此需要显示调用析构函数。

pc3->~JustTesting(); //destory object pointed to by pc3
pc1->~JustTesting(); //destory object pointed to by pc4

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