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What would you like to do?
Let's do a map-like function for C Language.
* The question is: What are function pointers used for and how would I use them?
* A simple case is like this:
* You have an array of operations according to you business logic. You have
* a hashing function that reduces an input problem to one of the business logic functions.
* A clean code would have an array an array of function pointers, and your program
* will deduce an index to that array from the input and call it.
* One quit common use case is a callback function. For example if you load
* something from a DB you can implement your loading function so that it
* reports the progress to a callback function. This can be done with function pointers.
* Let's do a map-like function for C.
#include <stdio.h>
int cube(int i) {
return i*i*i;
int mult(size_t i, int j) {
return i * j;
void apply(int *arr, size_t len, int (*fnPtr)(int)) {
for(size_t i = 0; i < len; ++i) {
arr[i] = fnPtr(arr[i]);
void apply_enumerate(int *arr, size_t len, int (*fnPtr)(size_t, int)) {
for(size_t i = 0; i < len; ++i) {
arr[i] = fnPtr(i, arr[i]);
void print_array(int *arr, size_t len, char *sep) {
if(sep == NULL) sep = ", ";
printf("%d", *arr);
for(size_t i = 1; i < len; ++i) printf("%s%d", sep, arr[i]);
#define ARRAY_SIZE(a) (sizeof(a)/sizeof((a)[0]))
int main() {
int arr[5] = {1,2,3,4,5};
print_array(arr, ARRAY_SIZE(arr), NULL);
apply(arr, ARRAY_SIZE(arr), cube);
print_array(arr, ARRAY_SIZE(arr), NULL);
apply_enumerate(arr, ARRAY_SIZE(arr), mult);
print_array(arr, ARRAY_SIZE(arr), NULL);
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