This...

[Aceix]

Can anyone please explain how 'this' is used. I do not want the explanation in this sites tut

[Zephilinox]

'this' is the memory address of the object of the class.

[Aceix]

Why does this code fail me?
Error: |40| error: invalid use of 'this' in non-member function|

#include <iostream>
//----------------------namespaces-----------------------------------------------
using namespace std;
//------------globals/functions'n'classes-prototypes-----------------------------
class C1;
class C2;

//-------------------------code--------------------------------------------------

class C1{virtual void dummy(){}};
class C2:public C1
{
    public:
        void check(C2*);
}obj1;


int main()
{
    C2 *p_obj2;

    try
    {
        C1 *p_obj1=new C1;
        p_obj2=static_cast<C2*>(p_obj1);

        if(p_obj2==0) cout<<"Failed...what this is pointing to is not a full object!!!";
        else cout<<"Great...working!!!";
    }
    catch(exception& e)
    {
        cout<<"Exception caught: "<<e.what();
    }
    obj1.check(&obj1);
    cin.get();
}

void check(C2 temp_obj)
{
    if(temp_obj==this) cout<<"Fine";
}

[R0mai]

This code should explain everything :

#include <iostream>

class Foo {
public:
    void print_my_address() { std::cout << this << std::endl; }    
};

int main() {
    Foo x;
    std::cout << &x << std::endl;
    x.print_my_address();
}

this is a way a member function can refer to the object it operates on.

EDIT: in your code you forgot to add the C2:: prefix before the check function on line 38.

[Aceix]

Thank you all!!!

[zb0S216C]

Aceix wrote:

"Why does this code fail me?"

Because you're using this outside the class context. It stems from how C++ implements member functions. Implicitly, all member functions contain a parameter, called this, which may be declared as ClassName * const this. When you invoke a member function from an object, the compiler will pass the address of the object you're calling the member function from to this of the member function you're calling. For example:

struct Sample
{
    void function(); // Compiler will add "Sample * const this" as a parameter.
};

int main()
{
    Sample sample;
    
    sample.function();
    // Here, the compiler will take the address of "sample" and give
    // it to the "this" parameter of "function()". "function()" will take
    // the address, and refer to "sample" with it.
}

Outside the class context, this is meaningless.

_Wazzak