problem with pointer to struct

M9000 · 07-30-2009, 03:18 PM

Hi, I'm new to C, I've only used C++ before. I have this problem with pointers to struct. This seems really elementary but I just can't find the solution.
It compiles all right, but causes segmentation fault. Here's the code:

Code:

typedef struct {
  int inumber;
  float fnumber;
} the_type;

int main() {
  the_type* N;
  N->inumber = 16; //this line causes segmentation fault - why?

  return 0;
}

bithub · 07-30-2009, 03:23 PM

You have a pointer to a the_type object. You DO NOT have an actual object -- just a pointer. What does that pointer point to? It points to some random location. You need to assign N to point to a valid object. For instance:

Code:

the_type* N;
the_type O;
N = &O;

// or...
the_type* N = malloc(sizeof(the_type));

M9000 · 07-30-2009, 03:31 PM

Thank you.

Elysia · 07-31-2009, 11:23 AM

This strikes me as odd: you've used C++ before, but this is exactly what would happen in C++, as well. And the solution is exactly the same (except new/delete instead of malloc/free).

07-30-2009, 03:18 PM	#1
M9000 Registered User Join Date: Jul 2009 Posts: 2	problem with pointer to struct Hi, I'm new to C, I've only used C++ before. I have this problem with pointers to struct. This seems really elementary but I just can't find the solution. It compiles all right, but causes segmentation fault. Here's the code: Code: typedef struct { int inumber; float fnumber; } the_type; int main() { the_type* N; N->inumber = 16; //this line causes segmentation fault - why? return 0; }
M9000 is offline

07-30-2009, 03:23 PM	#2
bithub Registered User Join Date: Sep 2004 Location: California Posts: 2,845	You have a pointer to a the_type object. You DO NOT have an actual object -- just a pointer. What does that pointer point to? It points to some random location. You need to assign N to point to a valid object. For instance: Code: the_type* N; the_type O; N = &O; // or... the_type* N = malloc(sizeof(the_type));
bithub is offline

07-30-2009, 03:31 PM	#3
M9000 Registered User Join Date: Jul 2009 Posts: 2	Thank you.
M9000 is offline

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