Thread: structures fooloing to look like classes

The only difference between structures and classes in C++ is that structures have public access by default and classes have private access by default. Otherwise they're exactly the same. In C the best you can get is pointers to functions.

Code:

#include <stdio.h>

typedef struct A {
  int x;
  void (*set)(struct A *, int);
  void (*print)(struct A);
} A;

void set(A *self, int x)
{
  self->x = x;
}

void print(A self)
{
  printf("%d\n", self.x);
}

int main(void)
{
  A obj = {10, set, print};

  obj.print(obj);
  obj.set(&obj, 20);
  obj.print(obj);
}

That is the beauty of C++ when considering Windows programming, too. We can easily extend otherwise unwieldy structures through inheritence. Here's a example of taking the WNDCLASSEX structure, and making it "smarter" by exploiting the C++ constructor, etc.






You can't do that with C !

thx but can we set up a lookalike constructors and destructors as well or virtual functions that we can reference later?


oh that one answered my question

very good example but is default the constructor?

thx but can we set up a lookalike constructors and destructors as well or virtual functions that we can reference later?

I'm not sure I follow you. constructors/destructors _must_ have the name of the class. They can always be referenced later.

If you mean "can we define contructors for pre-existing structures", of course not. But inheritance makes it possible to have the same functionality. Note that, when you DO derive from existing structures/classes such as WNDCLASSEX, never add members - only functions. Because when you add member variables, and then do something like:

RegisterClassEx(this);

...the function could fail.


[edit]

Yes, contructors/destructors are always called in C++.

[/edit]