What is purpose of a “this” pointer in C++? [duplicate]

Answer 1

It allows you to get around members being shadowed by method arguments or local variables.

Answer 2

Some points to be kept in mind

• This pointer stores the address of the class instance, to enable pointer access of the members to the member functions of the class.

• This pointer is not counted for calculating the size of the object.

• This pointers are not accessible for static member functions.

• This pointers are not modifiable

Look at the following example to understand how to use the 'this' pointer explained in this C++ Tutorial.

class this_pointer_example // class for explaining C++ tutorial 
{
    int data1;
 public:
    //Function using this pointer for C++ Tutorial
    int getdata()
    { 
        return this->data1;
    } 
  //Function without using this pointer 
  void setdata(int newval)
  {
       data1 = newval;
  }
};

Thus, a member function can gain the access of data member by either using this pointer or not. Also read this to understand some other basic things about this pointer

Answer 3

The this pointer inside a class is a reference to itself. It's needed for example in this case:

class YourClass
{
   private:
      int number;

   public:
      YourClass(int number)
      {
         this->number = number;
      }
}

(while this would have been better done with an initialization list, this serves for demonstration)

In this case you have 2 variables with the same name

1. The class private "number"
2. And constructor parameter "number"

Using this->number, you let the compiler know you're assigning to the class-private variable.

Answer 4

The double colon in c++ is technically known as "Unary Scope resolution operator". Basically it is used when we have the same variable repeated for example inside our "main" function (where our variable will be called local variable) and outside main (where the variable is called a global variable). C++ will alwaysexecute the inner variable ( that is the local one). So imagine you want to use the global variable "Conundrum" instead the local one just because the global one is expressed as a float instead of as an integer:

#include <iostream>
using namespace std;

float Conundrum=.75;

int main()
{
  int Conundrum =75;
  cout<<::Conundrum;

}

So in this case the program will use our float Conundrum instead of the int Conundrum.

Answer 5

• Helps in disambiguating variables.
• Pass yourself as a parameter or return yourself as a result

Example:

struct A
{
    void test(int x)
    {
        this->x = x;                 // Disambiguate. Show shadowed variable.
    }
    A& operator=(A const& copy)
    {
        x = copy.x;
        return *this;                // return a reference to self
    }

    bool operator==(A const& rhs) const
    {
         return isEqual(*this, rhs); // Pass yourself as parameter.
                                     // Bad example but you can see what I mean.
    }

    private:
        int x;
};

Answer 6

1. Resolve ambgiguity between member variables/functions and those defined at other scopes
2. Make explicit to a reader of the code that a member function is being called or a member variable is being referenced.
3. Trigger IntelliSense in the IDE (though that may just be me).