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Pointers to functions

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Pointers to functions

A useful technique is the ability to have pointers to functions. Their declaration is easy: write the declaration as it would be for the function, say

int func(int a, float b);

and simply put brackets around the name and a in front of it: that declares the pointer. Because of precedence, if you don't parenthesize the name, you declare a function returning a pointer:

/* function returning pointer to int */
int *func(int a, float b);

/* pointer to function returning int */
int (*func)(int a, float b);

Once you've got the pointer, you can assign the address of the right sort of function just by using its name: like an array, a function name is turned into an address when it's used in an expression. You can call the function using one of two forms:



(*func)(1 );
/* or */
func(1,2);

The second form has been newly blessed by the Standard. Here's a simple example.

#include <stdio.h>
#include <stdlib.h>

void func(int);

main()

void
func(int arg)

Example 5.16

If you like writing finite state machines, you might like to know that you can have an array of pointers to functions, with declaration and use like this:

void (*fparr[])(int, float) = ;
/* then call one */

fparr[5](1, 3.4);

Example 5.17

But we'll draw a veil over it at this point!



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