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int num_a = 1;
int const  *p_a = &num_a; //底层const
//*p_a = 2;  //错误，指向“常量”的指针不能改变所指的对象

int num_b = 2;
int *const p_b = &num_b; //顶层const
//p_b = &num_a;  //错误，常量指针不能改变存储的地址值

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int num_c = 3;
const int *p_c = &num_c;  //p_c为底层const的指针
//int *p_d = p_c;  //错误，不能将底层const指针赋值给非底层const指针
const int *p_d = p_c; //正确，可以将底层const指针复制给底层const指针

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nt num_e = 4;
const int *p_e = &num_e;
//*p_e = 5;  //错误，不能改变底层const指针指向的内容
int *p_f = const_cast<int *>(p_e);  //正确，const_cast可以改变运算对象的底层const。但是使用时一定要知道num_e不是const的类型。
*p_f = 5;  //正确，非顶层const指针可以改变指向的内容
cout << num_e;  //输出5

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int *p = new init ;
p = new int (10);
delete p;

int  **pp = new int * [10]{NULL};
delete []pp;

 #include <iostream>


int * p = new （std :: nothrow）int[8748315031785743515];
//不抛出异常返回NULL
set_new_handler

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(a = 0)&&(b = 100)  //a= 0 赋值返回 a 为 0 ，为假