BUET M.Sc Admission — Exam: 2018 (IICT)প্রশ্ন ও সমাধান

A function pointer is a variable that stores the address of a function (its entry point in code memory) instead of the address of data. Because a function's address is known at compile time, a function pointer lets you call that function indirectly, pass it as an argument, store it in an array/struct, and decide at run time which function actually executes — the basis of callbacks, dispatch tables, and simple plugin-style designs.

Declaration syntax: return_type (*pointer_name)(parameter_types);

Example:

#include <stdio.h>

int add(int a, int b) { return a + b; }
int sub(int a, int b) { return a - b; }

int main(void) {
    int (*fp)(int, int);     /* declare a function pointer */

    fp = add;                 /* point it at add()          */
    printf("Add: %d\n", fp(10, 4));   /* calls add() indirectly */

    fp = sub;                 /* now point it at sub()      */
    printf("Sub: %d\n", fp(10, 4));   /* calls sub() indirectly */

    return 0;
}

Output:

Add: 14
Sub: 6

Common real uses:

• Callback functions — e.g. the comparator passed to qsort(base, n, size, cmp).
• Dispatch/jump table — an array of function pointers indexed by a command code, replacing long if-else/switch chains:

int (*ops[2])(int, int) = { add, sub };
printf("%d\n", ops[0](5, 3));   /* calls add(5,3) -> 8 */

• Implementing simple state machines and plugin-style, run-time-selectable behaviour.

Exam takeaway: a function pointer stores a code address, is declared as return_type (*name)(params), and is invoked exactly like the function itself (fp(args)) — enabling indirection and runtime selection of behaviour.