Function pointer not returning a value

Question

We just learnt in school about function pointers in C and i wanted to try them out in a test program. The idea is obviously pretty simple. However, when i try to use result = (*funcPtr)(); i get an STATUS_ACCESS_VIOLATION exception but i can't tell what i did wrong. Any ideas on what i'm missing?

#include <stdio.h>

int fun1();
int fun2();

int (*funcPtr)(void);

int fun1() {
  return 1;
}

int fun2() {
  return 2;
}

int main(void) {
  int input,result = 0;
  scanf("%d",input);
  if(input == 1) {
    funcPtr = &fun1;
  } else if(input == 2) {
    funcPtr = &fun2;
  }
  result = (*funcPtr)();
  printf("%d\n",result);
}

It's problem with scanf (scanf("%d",input);) not with function pointer. You are missing&. — kiran Biradar
– kiran Biradar, Commented Nov 5, 2018 at 16:06
Don't forget to handle the case where input is neither 1 nor 2. — 0x5453
– 0x5453, Commented Nov 5, 2018 at 16:06
You might want to learn how to debug your programs. Especially how to use a debugger to catch crashes as they happen to locate where in your code the problem is. — Some programmer dude
– Some programmer dude, Commented Nov 5, 2018 at 16:07
You should really include (void) in place of () in the function declarations and definitions. There is a difference. — Jonathan Leffler
– Jonathan Leffler, Commented Nov 5, 2018 at 16:08

kalehmann · Accepted Answer · 2018-11-05 18:40:10Z

4

You forgot a & before input in the scanf. Therefore scanf writes not to the address of the input variable, but to its value (and the variable is uninitialized a this point).

Change that line to:

scanf("%d", &input);

to pass a pointer to input to scanf and not the value of input.

And as already pointed out by other users, do not forget to handle inputs other than 1 and 2. Otherwise you will call your uninitialized funcPtr variable, which most likly results in a Segmentation fault.

edited Nov 5, 2018 at 18:40

answered Nov 5, 2018 at 16:07

kalehmann

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3 Comments

Stelios Papamichail Over a year ago

Thank you, you and the others who commented pointed me in the right direction.

absoluteAquarian Over a year ago

i should probably mention that input will actually be garbage data, not 0.

kalehmann Over a year ago

Thank you @Tau, you are right. I have updated my answer

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