Function Pointer in C

Overview

• Function pointers in C are similar to normal data pointers (e.g., int *, char *), but they point to code rather than data.
• They store the start of executable code of a function.

Example of Function Pointer Declaration and Use

• Basic Example: #include<stdio.h> void fun(int a) { printf("Value of a is %d\n", a); } int main() { void (*fun_ptr)(int) = &fun; (*fun_ptr)(10); return 0; } Output: Value of a is 10

Explanation

• Brackets are necessary around function pointer declaration to avoid confusion with function returning a pointer.
• Function pointers point to code, unlike data pointers.

Interesting Facts

1. Function pointers point to code, unlike normal pointers that point to data.

2. No memory allocation/deallocation is needed for function pointers.

3. Function names can be used to get their address directly.

   • Example of simplified code without & and * operators: void (*fun_ptr)(int) = fun; fun_ptr(10);

4. Arrays of function pointers can be created:

   void (*fun_ptr_arr[])(int, int) = {add, subtract, multiply};

5. Function pointers can replace switch-case constructs.

6. Function pointers can be passed as arguments and returned from functions.

Practical Use Cases

• Sorting and Searching with function pointers: int compare(const void *a, const void *b) { return (*(int*)a - *(int*)b); } qsort(arr, n, sizeof(int), compare);
• A generalized search function can utilize function pointers: int search(void *arr, int arr_size, int ele_size, void *x, bool compare(const void*, const void*))

Object-Oriented Features in C++

• Many C++ features like virtual functions are implemented using function pointers in C.

Related Concepts

• How to declare a pointer to a function.
• Understanding C++ function call by pointer.
• Difference between pointers and arrays in C.

Summary

• Function pointers provide flexibility and capability for dynamic execution of functions in C.
• They can help avoid code redundancy and allow for cleaner code architecture by allowing functions to be passed around and executed dynamically.