5.6. 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)(1,2);
/* 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 (*fp)(int);
fp = func;
(*fp)(1);
fp(2);
exit(EXIT_SUCCESS);
}
void
func(int arg){
printf("%d\n", 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) = {
/* initializers */
};
/* 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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