C++ 深入理解C++的new 和delete

(1)new delete ，称为运算符；delete和free称作C的库函数

(2)new 不仅可以做内存开辟，还可以做内存初始化操作；malloc仅开辟内存；

(3)malloc开辟内存失败，是通过返回值和nullptr做比较；而new 开启内存失败，是通过抛bad_alloc类型的异常来判断的

#include 
#include 
int main()
{
  int *p = (int *)malloc(sizeof(int));//分配内存
  if (nullptr == p) {   //判断返回值
    return -1;
  }

  *p = 2;//初始化
  free(p);//释放

  int * p1;
  try
  {
     p1 = new int(2);//分配内存并初始化
  }
  catch (const std::bad_alloc & e)//判断是否抛异常
  {
  	
  }

  delete p1;
  return 0;
}

free 直接传入地址

delete [] p 释放数组；delete p 释放单个元素

#include 
#include 
int main()
{
  //1 抛异常new
  int * p1;
  try
  {
     p1 = new int(2);//分配内存并初始化
  }
  catch (const std::bad_alloc & e)//判断是否抛异常
  {
  	
  }

 //2 不抛异常new
  int *p2 = new (std::nothrow)int();//不抛异常

  //3 开辟常量内存
  const int *p3 = new const int(40);//开辟一个常量

  //4 定位new
  int data = 0;
  int *p4 = new(&data) int(50);//在指定地址内存初始化，本身并不开辟内存，只负责初始化

  delete p1;
  delete p2;
  delete p3;
  delete p4;
  return 0;
}