[c++] typedef class

[vivendi]

If i have the following class:

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"

[laserlight]

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

[ovidiucucu]

[ Moved thread ]

[vivendi]

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

[laserlight]

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).

[krmed]

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

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

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.

[ninja9578]

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:

cBlaat * blaat = NULL;

[laserlight]

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.

[rohshall]

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.

[laserlight]

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()?

[ninja9578]

The function is also used, but never defined.

Remember that

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

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.

[Paul McKenzie]

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