[c++] typedef class

If i have the following class:

Code:

---

class cBlaat
{
public:
  void SomeFunc();
};

typedef class cBlaat * LPBLAAT;

---

Then what does that last line mean?? What could be the reason for this..??
"typedef class cBlaat * LPBLAAT"

It just makes LPBLAAT an alias for the type cBlaat*. The class keyword in the typedef is unnecessary.

[ Moved thread ]

Ok thanks, then i have another question about a class. Suppose i have the following code:

Code:

---

class cBlaat
{
public:
  DoSomething();
};

cBlaat * blaat;  //doesn't work

int main()
{
blaat->DoSomething();
return 0;
}

---

Why doesn't "cBlaat * blaat" work when i declare it outside of a function, but does it work when i declare it as "cBlaat blaat" ??
I just don't get what's so different about it...

Quote:

---

Originally Posted by vivendi

Why doesn't "cBlaat * blaat" work when i declare it outside of a function, but does it work when i declare it as "cBlaat blaat" ??

---

It works, but looking at your sample code (which will not even compile), you probably tried to dereference the pointer when it did not point to an object (in this case, it is a null pointer).

Quote:

---

Originally Posted by vivendi

Why doesn't "cBlaat * blaat" work when i declare it outside of a function, but does it work when i declare it as "cBlaat blaat" ??
I just don't get what's so different about it...

---

To expand on what laserlight said...

The first

Code:

---

cBlaat *blaat;

---

only declares a pointer to a cBlaat object - it does not create an instance of the object - you only have an invalid pointer at this point.

The second

Code:

---

cBlaat blaat;

---

actually creates an instance of the cBlaat object - so you actually have one of those objects existing and can operate on it.

Hope that helps.

Quote:

---

Originally Posted by laserlight

It works, but looking at your sample code (which will not even compile), you probably tried to dereference the pointer when it did not point to an object (in this case, it is a null pointer).

---

No it's not, it's an undefined pointer, unless my terminology of what a null pointer is is wrong. I think a null pointer is this:

Code:

---

cBlaat * blaat = NULL;

---

Quote:

---

Originally Posted by ninja9578

No it's not, it's an undefined pointer, unless my terminology of what a null pointer is is wrong.

---

Notice that it has static storage duration, hence it is zero initialised.

Quote:

---

Originally Posted by laserlight

Notice that it has static storage duration, hence it is zero initialised.

---

Yes, but I think it should compile (at least after looking at it, I don't see any compilation error). Runtime error? yes.

Quote:

---

Originally Posted by rohshall

Yes, but I think it should compile (at least after looking at it, I don't see any compilation error).

---

What's the return type of cBlaat::DoSomething()? ;)

The function is also used, but never defined.

Remember that

Code:

---

class foo {
  void DoSomething(void);
};

void foo::DoSomething(void){
  std::cout << "Hello World" << std::endl;
}

foo * bar;

main(){
  bar -> DoSomething();
}

---

Is undefined behavior, but stable on almost every compiler.

Also, why do statically declared pointers initialize to zero? Seems like a waste of a mov command to me. I always do this

Code:

---

foo * bar = 0;

---

If I want to know if the pointer has been initialized or not later. If I omit the zero, I don't care what it is.

Quote:

---

Originally Posted by ninja9578

Also, why do statically declared pointers initialize to zero? Seems like a waste of a mov command to me.

---

If it were not initialized to 0, then the compiler is broken. The rule that globals and statics are initialized to 0 goes back to 'C' programming.

Regards,

Paul McKenzie