geeksforgeeks 021-c++中的this指针

函数调用链

#include<iostream>
using namespace std;
 
class Test
{
private:
  int x;
  int y;
public:
  Test(int x = 0, int y = 0) { this->x = x; this->y = y; }
  Test &(int a) { x = a; return *this; }
  Test &setY(int b) { y = b; return *this; }
  void print() { cout << "x = " << x << " y = " << y << endl; }
};
 
int main()
{
  Test obj1(5, 5);
 
  
  // as the same object is returned by reference
  obj1.setX(10).setY(20);
 
  obj1.print();
  return 0;
}

Output:

1	x = 10 y = 20

对于一个类X，this指针是X const
如果一个成员函数X被声明为const，this指针为const X const

#include<iostream>
class X {
   void fun() const {
    // this is passed as hidden argument to fun().
    // Type of this is const X*
    }
};
#include<iostream>
class X {
   void fun() volatile {
     // this is passed as hidden argument to fun().
     // Type of this is volatile X*
    }
};
#include<iostream>
class X {
   void fun() const volatile {
     // this is passed as hidden argument to fun().
     // Type of this is const volatile X*
    }
};

delete最好不要用在this指针上面，如果使用，需要考虑下面的情况

delete操作只对使用了new的对象有效

class A
{
  public:
    void fun()
    {
        delete this;
    }
};
 
int main()
{
  /* Following is Valid */
  A *ptr = new A;
  ptr->fun();
  ptr = NULL // make ptr NULL to make sure that things are not accessed using ptr.
 
 
  /* And following is Invalid: Undefined Behavior */
  A a;
  a.fun();
 
  getchar();
  return 0;
}

delete之后，所有的成员都不可以访问

#include<iostream>
using namespace std;
 
class A
{
  int x;
  public:
    A() { x = 0;}
    void fun() {
      delete this;
 
      /* Invalid: Undefined Behavior */
      cout<<x;
    }
};

geeksforgeeks 021-c++中的this指针

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