Passing an array as an argument to a function pointer in C

Question

I'm currently studying pointers to functions and have been practicing on sort array functions. The point is I input a sequence of numbers into the function and the program will re arrange it in ascending order. It worked just fine when I do a call by value function (I think that's how you call it). However when I try to assign a pointer to function and try to use that pointer instead of the function itself, it returns a bunch of errors. I'm sure the problem is due to the fact that I'm passing an array as an argument to the function POINTER. Here is my code:

#include<stdio.h>
#define SIZE 10
void sort(int a[], int size);
void swap(int *elt1, int *elt2);
main()
{
 int i; int array[SIZE]= {1,9,3,2,4,100,43,23,32,12};
 void (*fptr)(int array, int SIZE);
 fptr = &sort;
 (*fptr)(array,SIZE);
 /*sort(array, SIZE);*/
 for(i=0;i<SIZE;i++)
 {
 printf("%d\n", array[i]);
 }
 return 0;
}
void sort(int a[], int size)
{
 int pass, j;
 for(pass = 0; pass<size;pass++)
 {
 for(j=0;j<size;j++)
 {
 if(a[j]>a[j+1])
 {
 swap(&a[j], &a[j+1]);
 }
 }
 }
}
void swap(int *elt1, int *elt2)
{
 int hold;
 hold = *elt1;
 *elt1 = *elt2;
 *elt2 = hold;
}

• Jack: The types of void (*fptr)(int array, int SIZE) don't seem the same of void sort(int a[], int size).
• user529758: @Jack They may not seem to be the same, but they are.
• Jack: @H2CO3 and int and a pointer to int? Actually I pointed out your same issue so I don't see your point.
• WhozCraig: @H2CO3 help the slow guy (me). When is an int synonymous with an int* (intptr_t not withstanding =P)
• WhozCraig: @H2CO3 had to qualify that, or I just knew you'd bring it to the table =P

Answer 1

The first argument of the function is a pointer to int (that is, int *), and not int.

void (*fptr)(int array, int SIZE);

should be

void (*fptr)(int *array, int SIZE);

• user2059456: H2CO3, thanks but its still not working.. Here is what I get: sortpointeragain.c:9: error: expected ‘;’, ‘,’ or ‘)’ before numeric constant sortpointeragain.c:10: error: ‘fptr’ undeclared (first use in this function) sortpointeragain.c:10: error: (Each undeclared identifier is reported only once sortpointeragain.c:10: error: for each function it appears in.)
• Jack: @user2059456: did you notice that your second parameter here: void (*fptr)(int array, int SIZE) has the same name of a #define? What happens is that preprocessor replaces it to void (*fptr)(int array, int 10) which is obviously not correct. Use a different name.
• user2059456: Yeah I tried to define SIZE to be 10 and use it as size of the array.. I'll try using another name.. get back to you in a second
• user2059456: Jack man you rock. You were right!!! But why can't I do such a thing.. I'm defining SIZE to be 10 which is an int and the pointer to function is expecting an int so it should be fine right???
• user2059456: OOOOHHH I see, the pointer is expecting a VARIABLE of type integer not just a number thrown in..... Am I right?