Slicing problem

[beakie]

I have 3 classes, myForm, myFormTest and myFormManager.

This is a simple version of what I have

class myFormManager {
myForm * formPointers;

void addForm(myForm &theform)
//code to add theform to formPointers
}

int execsomefunction(int formIndex) {
  return formPointers[formIndex].somefunction();
}

class myForm {
int somefunction();
}

class myFormTest: public myForm {
int somefunction(); //override
}

So I created some code with an instance of both the myFormTest class and the myFormManager class and add the form using myFormManager.addForm(). when i call execsomefunction() in the manager class it runs but doesnt perform the override.

I realise "slicing" is occurring and I believe I understand WHY it is happening... but I don't know what to change to resolve it. myFormManager knows nothing about the myFormTest class only the myForm class... so how can I make it execute the override???? Ummmm

(I think) my first mistake is that I am adding an instance of myForm rather than a reference to an instance of myForm defined in the main(). I am not quite sure how to do this.

(I think) my second mistake is that the manager only knows about myForm not myFormTest so any reference I make in this class will cause slicing to occur.

Any help would be appreciated.

[1yR4jE8b]

myForm::someFunction needs to be marked as virtual.

[beakie]

Needs? Really?

I thought that was only if it was a "must override" situation.

somefunction() in both classes contains code. I only want to override it sometimes?

Are you sure?



Edit: Just tried it anyway and it didn't fix the problem.

[o1vk4iN6]

You should post all relevant code, i'm just filling in some blanks.

You have an array of myForm, so when you add a new form you are only creating a copy of myForm. All other data regarding the vtable and myFormTest's variables won't be stored. You need an array of pointers to myForm, so you are not actually storing a myForm.

myForm form1 = myFormTest();
myForm *form2 = new myFormTest();

form1.somefunction(); // myForm::somefunction()
form2->somefunction(); // myFormTest::somefunction() 

[beakie]

I do need the virtual bit... I was wrong. Googled it...

You have an array of myForm, so when you add a new form you are only creating a copy of myForm. All other data regarding the vtable and myFormTest's variables won't be stored. You need an array of pointers to myForm, so you are not actually storing a myForm.

Awesome. Worked a treat! Thanks!