difference between calling constructors?

[cpthk]

If I have a class ABC for example. What's the different between these calls?

class ABC{

  ABC(){


  }

}

ABC var1;

ABC var2();

ABC var3 = new ABC();
I know var3 gets a pointer to the class ABC in heap. What about var1 and var2?


Thanks.

[laserlight]

This creates an object, named var1, of type ABC:

ABC var1;

This declares a function, named var2, that takes no arguments and returns an object of type ABC:

ABC var2();

This will result in a compile error:

ABC var3 = new ABC();

You probably meant to write:

ABC* var3 = new ABC();

[ltcmelo]

If I have a class ABC for example. What's the different between these calls?

class ABC{

  ABC(){


  }

}

You missed a semi-colon at the end of the class definition.

ABC var1;

This creates a stack object of type ABC.

ABC var2();

This is the declaration of a function named var2 which has no parameters an returns an ABC object by value.

ABC var3 = new ABC();

As you said, this creates an ABC object in the free store - sometimes also called the heap, but I really don't want to get into a philosophical discussion about memory area names . Just notice that you forgot the * indicating a pointer. The correct form would be:

ABC * var3 = new ABC();

And since you started it, there's also...

ABC * var4 = new ABC;

Which for non-POD (plain old data) structures is basically the same thing as the third case.

[cpthk]

ABC var2();

does var2 call the constructor in the class?

[ZuK]

No. This is just a function declaration. ( see prev. posts ).
you propably want

ABC var2;

Kurt

[cpthk]

No. This is just a function declaration. ( see prev. posts ).
you propably want

ABC var2;

Kurt

So what if I have two constructor

class ABC{
    ABC(){
      ...
    }
    ABC(int i){
      ...
    }
};

ABC varA;

This calls default constructor.

ABC varB(1);

This calls the constructor that takes an integer.

ABC varC();

This is a varC function declaration that returns object of type ABC.

Is this what you guys meant? Is so, varA and varB are kind of confusing, since you need "()" for constructor that takes parameters but you do not need "()" at all if constructor do not take parameters.

[ltcmelo]

So what if I have two constructor

class ABC{
    ABC(){
      ...
    }
    ABC(int i){
      ...
    }
};

ABC varA;

This calls default constructor.

ABC varB(1);

This calls the constructor that takes an integer.

ABC varC();

This is a varC function declaration that returns object of type ABC.

Is this what you guys meant? Is so, varA and varB are kind of confusing, since you need "()" for constructor that takes parameters but you do not need "()" at all if constructor do not take parameters.

Yes, you've got it. It might be confusing at first, but you'll get used to it. That's C++ parsing.