change the pointer referenced variable in a function

Question

I have created a pointer variable to point to an active variable. I have two variables, I want to toggle the active variable between these two variables. Managed to do this inside the main. Now I want to extend this to another function

int main()
{
    int x = 0;
    int y = 0;
    int *active=&y;

    if(active == &x)
       active = &y;
    else
       active = &x;

}

I dont want to swap the values of the variables, x, y.

x, y are coordinates of a cartesian plane.

noone · Accepted Answer · 2019-12-01 01:17:53Z

1

You can pass the reference of the pointer variable to the function, and in the formal parameter list create a pointer which holds the memory address of the pointer variable

void flip(int **act, int *x, int *y){
    if(*act == x){
        *act = y;
    }else{
        *act = x;
    }
}
int main()
{
    int x = 0;
    int y = 0;
    int *active=&y;

    flip(&active, &x, &y);

}

edited Dec 1, 2019 at 1:17

answered Nov 30, 2019 at 23:54

noone

6,5782 gold badges48 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Dmitri Over a year ago

Maybe you meant void flip(int **act, int *x, int *y)?

noone Over a year ago

Can you please submit you answer as well ? Here I have passed the reference of the pointer variable to the function

John Bollinger Over a year ago

@NuOne, you have passed a pointer to the pointer variable to function flip. C does not have references. You have also passed pointers to main's local x and y variables. But the types of those arguments do not match the declared type's of flip()'s parameters, so the program has undefined behavior. Your compiler should at least be warning about that. If it isn't, then either turn up the warning level or get a better compiler. Your program might happen to work correctly on some systems, with some compilers, but it will definitely malfunction on others.

noone Over a year ago

@JohnBollinger can you suggest an answer

John Bollinger Over a year ago

@NuOne, Dmitri already told you how to correct your code. No other change is required.

Collectives™ on Stack Overflow

change the pointer referenced variable in a function

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related