The this pointer

The this pointer is a pointer accessible only within the nonstatic member functions of a class, struct, or union type. It points to the object for which the member function is called. Static member functions don't have a this pointer.

Syntax

this
this->member-identifier

Remarks

An object's this pointer isn't part of the object itself. It's not part of the result of a sizeof statement on the object. When a nonstatic member function is called for an object, the compiler passes the object's address to the function as a hidden argument. For example, the following function call:

myDate.setMonth( 3 );

can be interpreted as:

setMonth( &myDate, 3 );

The object's address is available from within the member function as the this pointer. Most this pointer uses are implicit. It's legal, though unnecessary, to use an explicit this when referring to members of the class. For example:

void Date::setMonth( int mn )
{
   month = mn;            // These three statements
   this->month = mn;      // are equivalent
   (*this).month = mn;
}

The expression *this is commonly used to return the current object from a member function:

return *this;

The this pointer is also used to guard against self-reference:

if (&Object != this) {
// do not execute in cases of self-reference

Occasionally, the this pointer is used directly—for example, to manipulate self-referential data structures, where the address of the current object is required.

Example

// this_pointer.cpp
// compile with: /EHsc

#include <iostream>
#include <string.h>

using namespace std;

class Buf
{
public:
    Buf( char* szBuffer, size_t sizeOfBuffer );
    Buf& operator=( const Buf & );
    void Display() { cout << buffer << endl; }

private:
    char*   buffer;
    size_t  sizeOfBuffer;
};

Buf::Buf( char* szBuffer, size_t sizeOfBuffer )
{
    sizeOfBuffer++; // account for a NULL terminator

    buffer = new char[ sizeOfBuffer ];
    if (buffer)
    {
        strcpy_s( buffer, sizeOfBuffer, szBuffer );
        sizeOfBuffer = sizeOfBuffer;
    }
}

Buf& Buf::operator=( const Buf &otherbuf )
{
    if( &otherbuf != this )
    {
        if (buffer)
            delete [] buffer;

        sizeOfBuffer =  strlen( otherbuf.buffer ) + 1;
        buffer = new char[sizeOfBuffer];
        strcpy_s( buffer, sizeOfBuffer, otherbuf.buffer );
    }
    return *this;
}

int main()
{
    Buf myBuf( "my buffer", 10 );
    Buf yourBuf( "your buffer", 12 );

    // Display 'my buffer'
    myBuf.Display();

    // assignment operator
    myBuf = yourBuf;

    // Display 'your buffer'
    myBuf.Display();
}

my buffer
your buffer

Type of the this pointer

The this pointer's type changes depending on whether the function declaration includes the const and/or volatile keywords. The following syntax describes the type of this in a member function:

[cv-qualifier-list] class-type * const this

The member function's declarator determines cv-qualifier-list. It can be const or volatile (or both). class-type is the name of the class.

The this pointer can't be reassigned. The const or volatile qualifiers used in the member function declaration apply to the class instance the this pointer points at, in the scope of that function, as shown in the following table:

The following table explains more about const and volatile.

Semantics of this modifiers

It's an error to pass a const object to a member function that isn't const.

Similarly, it's also an error to pass a volatile object to a member function that isn't volatile.

Member functions declared as const can't change member data. In const functions, the this pointer is a pointer to a const object.

See also

Keywords