Setting a user-defined class to NULL

[Willfrost]

I would like to declare an instance of a class, but set it equal to NULL and wait until later to initialize it with a constructor. This can certainly be done with a string as in the example below:

#include <string>

using namespace std;

string name = NULL;

int main(){
    name = string("Billybob");
    return 0;
}

Why can't I do it with a class I've defined, such as:

class circle{
    private:
        int radius;
    public:
        circle(int rad){
            radius = rad;}
};

circle red_circle = NULL;

int main(){
    red_circle = circle(20);
    return 0;
}

When I do this, it compiles but my compiler (Dev-C++) gives the warning: "passing NULL used for non-pointer converting 1 of `circle::circle(int)'"

I know this is a super-noob question and I appreciate you taking the time to help me.

Thanks,

Will

[Zaita]

You cannot assign a variable to the value null if it's of an object type. Only pointers can be set to null.

e.g

circle *red_circle = NULL;

int main() {
 red_circle = new circle(20);

 delete red_circle; // You have to delete the memory allocated with new
 return 0;
}

http://www.cplusplus.com/doc/tutorial/dynamic.html

[Willfrost]

Thanks for the info! That makes sense to me, but why don't you have to call "new" and subsequently "delete" when you're doing it with a string object? Are the new and delete calls built into the constructor/destructor?

EDIT: While trying to answer this problem myself I went looking for the source code for the C++ string class but was unable to find it. Does anyone know of a website that has the source code for any classes such as <string> <time> <iostream>?

Thanks,

Will

[Zaita]

The string constructor and function calls will handle the allocation and de-allocation for you behind the scenes.

[Willfrost]

Got'cha! Thanks again. This has been a big help!

Will

[helios]

Does anyone know of a website that has the source code for any classes such as <string> <time> <iostream>?

How about the GCC sources?