Segmentation Fault, pointer issue?

Question

I'm pretty new to C coding, and pointers are something I'm having a lot of trouble with. I'm trying to write a program that takes in 2 pointers as parameters, adds the value of the first to the second, then returns the value of the first. What I've written is this:

int foo(int *g, int *h)
{ 
    int a;
    a = *g; 
    *h += a;
    return a; 
}

However, I am getting a segmentation fault error using an online compiler. I read that these are caused by rogue pointers, but I'm not sure where the error is. Can someone help?

EDIT: I'm calling this function this way:

    main()
{
   int* x;
   *x = 3;
   int* y;
   *y = 4;
   int z = foo(x, y);
   printf("%d", z);
}

I thought that was the way to declare a pointer, and that using (*) to dereference it was how to assign it a value. Am I incorrect?

How are you calling this function? Show us a short full example — halex
– halex, Commented Mar 3, 2014 at 16:37

HelloWorld123456789 · Accepted Answer · 2014-03-03 16:44:54Z

3

In main you have to allocate spaces for x and y before you can use it. If x and y are not allocated spaces, they point to arbitrary memory locations. If they are outside of your program segment, you will get a segmentation fault.

main()
{
   int* x=malloc(sizeof(int));
   *x = 3;
   int* y=malloc(sizeof(int));
   *y = 4;
   int z = fun(x, y);
   printf("%d", z);
}

Or like this:

main()
{
   int x=3,y=4;
   int z = fun(&x, &y);
   printf("%d", z);
}

answered Mar 3, 2014 at 16:44

HelloWorld123456789

5,3693 gold badges25 silver badges33 bronze badges

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

1 Comment

Adam Eisenstein Over a year ago

Thanks! I was worried that it was a problem with the foo code, but it turns out it was, in fact, how I was declaring the variables. Your second solution worked perfectly.

Jabberwocky · Accepted Answer · 2014-03-03 16:46:05Z

0

This will cause a segfault because you are dereferencing a pointer that has not been initialized.

 int *x;    // declares pointer X
 *x = 3;    // seg fault here because x contains garbage and points certainly to 
            // invalid memory

answered Mar 3, 2014 at 16:46

Jabberwocky

51.3k18 gold badges71 silver badges127 bronze badges

Collectives™ on Stack Overflow

Segmentation Fault, pointer issue?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related