内存分配与对象构造的分开

#include <iostream>
#include <memory>
using namespace std;

class T
{
public:
    T() {cout << "construct" << endl;}
    ~T() {cout << "destruct" << endl;}
};

int main()
{
    T *t1;
    //operator new函数:获取未构造内存
    t1 = static_cast<T *>(operator new(sizeof(T))); 
    //定位new表达式：在特定的、预分配的内存地址构造一个对象
    //new (place_address) tpye
    //new (place_address) type (initializer-list)
    new (t1) T;    
    //对于使用定位new表达式构造对象的程序，显式调用析构函数
    t1->~T();
    //operator delete函数：释放指定内存，不会运行析构函数
    operator delete(t1);

    allocator<T> at;
    T *t2, t3;
    t2 = at.allocate(sizeof(T));
    at.construct(t2, t3);
    at.destroy(t2);
    at.deallocate(t2, sizeof(T));
    return 0;
}