如何通过指针更改类成员的值

Question

This function is part of a class called ClipInterface which provides a GUI to edit some member values from a given Clip object.

To a complish that, I am using this function that receives a Clip object by pointer, and then it access to some of its members to modify them as follows:

void ClipInterface::update(Clip* _clip){
//p_clip is a pointer declared in the .h file so it can 
//work across the whole class

    p_clip = _clip;

    for (int i = 0; i < p_clip -> stepSequence.size(); ++i){
        stepToggles[i] -> active = p_clip -> stepSequence[i];        
    }

    for (int i = 0; i < p_clip -> stepSequence.size(); ++i){
        *p_clip -> stepSequence[i] = stepToggles[i] -> active;
    }
}

By using the previous expression, the program compiles but then it gives me a segmentation fault error when i try tu run it.

The questions are:

• how do i modify a class member value by pointer? i tried what is here but i get a segmentation fault.

• what in this expresion y causing the segmentation fault?

thanks in advance.

Answer 1

*p_clip -> stepSequence[i] = stepToggles[i] -> active;

in here p_clip is already a pointer you should use;

p_clip -> stepSequence[i] = stepToggles[i] -> active;

To access members of a structure through a pointer, use the arrow operator.

Answer 2

You can use either one of these

(*p_clip).stepSequences[i] = stepToggle

Where you first derefrence the pointer to get the object then get the member

Or use the arrow operator which is equivalent and have the same effect

p_clip->stepSequences[i] = stepToggle