程序代码：

#include <iostream>
#include <new>
#include <cstdio>
using namespace std;

struct A
{
    void *operator new(size_t size) 
    {
        cout<<"operator new"<<endl;
        malloc(size);
    }
    void operator delete(void *p)
    {
        cout<<"operator delete"<<endl;
        free(p);
    }
    
    void *operator new(size_t size,const nothrow_t &thorw_value) noexcept
    {
        cout<<"operator new noexcept"<<endl;
        malloc(size);
    }
    void operator delete(void *p,const nothrow_t &nowthrow_value) throw()
    {
        cout<<"operator delete noexpect."<<endl;
        free(p);
    }
}; 

int main()
{
    A *a1=new A;
    delete a1;
    
    A *a2=new(nothrow) A;
    delete a2;//为什么调用的是 operator delete 而不是  operator delete noexpect
    return 0;
}