Thread: Can a pointer to a class be null?

I want some of my pointer to point to NULL but I'm not sure if this is possible. Does anyone know how I can define a pointer to NULL? I kept getting this error somewhere else in my code when I checked for null pointers.

"Error c2676 binary '==': 'Object' does not define this operator or a conversion to a type acceptable"


This is how I did my pointer defining. Pointers in my code only get defined in one place no matter what.

Code:

int Total_sv_Objects;
Total_sv_Objects = MAX_ITEM - 50;


//Class Object
Object *item[MAX_ITEM]

for (int i = 0; i < Total_sv_Objects ; i++)
{

item = new (Something, ect);
 
}

for (int i = Total_sv_Objects; i <  MAX_ITEM; i++)
{
//Not being used
item = NULL;
}

Originally Posted by LAURENT*

Can a pointer to a class be null?

By "pointer to a class" you presumably mean "pointer to an object of class type", in which case the answer is yes.

Originally Posted by LAURENT*

Does anyone know how I can define a pointer to NULL?

Pre-C++11, you would use:

Code:

ptr = 0;
// or:
ptr = NULL;

As of C++11, you would use:

Code:

ptr = nullptr;

Originally Posted by LAURENT*

"Error c2676 binary '==': 'Object' does not define this operator or a conversion to a type acceptable"

This means that you tried to call operator== on an object of the Object class, but you did not overload operator== for it. The code that you posted does not contain such a mistake, so you may have posted code that is not relevant.

Originally Posted by laserlight

By "pointer to a class" you presumably mean "pointer to an object of class type", in which case the answer is yes.


Pre-C++11, you would use:

Code:

ptr = 0;
// or:
ptr = NULL;

As of C++11, you would use:

Code:

ptr = nullptr;

This means that you tried to call operator== on an object of the Object class, but you did not overload operator== for it. The code that you posted does not contain such a mistake, so you may have posted code that is not relevant.

I just noticed the real problem. It was a problem with a function argument. Apparently I wrote something like this.

Code:

Void function (Class *square)
{
 //Stuff goes here
}

Instead of

Code:

Void function (Class *square[])

{
//Stuff, whatever...
}

Anyways thanks for clearing up what's possible.

Originally Posted by LAURENT*

I just noticed the real problem. It was a problem with a function argument. Apparently I wrote something like this.

Code:

Void function (Class *square)
{
 //Stuff goes here
}

Instead of

Code:

Void function (Class *square[])

{
//Stuff, whatever...
}

Anyways thanks for clearing up what's possible.

You might look into doing it like:

Code:

    void func (const std::vector<Class*>& squares) {}

Or even:

Code:

    void func (const std::vector<std::shared_ptr<Class>>& squares) {}
    // You could do a typedef to make declaring it shorter

Just a thought anyway. I'm currently rewriting a game engine myself, and I'm using the shared_ptr and container classes quite a lot, they are really convenient. Although I want to write some specialized array like containers myself for a "Graph" class (like

Code:

Graph<SDL_Texture*>

or

Code:

Graph<std::shared_ptr<Vertice>>

, or whatever, just to have member functions that can operate/query many things at once).