In the snippet below:
#include <stdio.h>
void swap (int*, int*);
// ^----(1)
int main (void) {
int a = 21;
int b = 17;
swap(&a, &b);
printf("a = %d, b = %d\n", a, b);
return 0;
}
void swap (int *pa, int *pb) {
// ^----(2)
int t = *pa;
*pa = *pb;
*pb = t;
return;
}
Which of these between (1) and (2) can be considered as a function prototype?
If a function is declared but not implemented it’ll usually cause a linking error… And sometimes (with older compilers) a runtime error.
The standard here is that the declaration (1) would be in a .h file that other .c files might reference while the implementation (2) would be in a .c so it is only built once into a .o file during compilation & linking.