C Language Pointers Function pointers
Example
Pointers can also be used to point at functions.
Let's take a basic function:
int my_function(int a, int b)
{
return 2 * a + 3 * b;
}
Now, let's define a pointer of that function's type:
int (*my_pointer)(int, int);
To create one, just use this template:
return_type_of_func (*my_func_pointer)(type_arg1, type_arg2, ...)
We then must assign this pointer to the function:
my_pointer = &my_function;
This pointer can now be used to call the function:
/* Calling the pointed function */
int result = (*my_pointer)(4, 2);
...
/* Using the function pointer as an argument to another function */
void another_function(int (*another_pointer)(int, int))
{
int a = 4;
int b = 2;
int result = (*another_pointer)(a, b);
printf("%d\n", result);
}
Although this syntax seems more natural and coherent with basic types, attributing and dereferencing function pointers don't require the usage of & and * operators. So the following snippet is equally valid:
/* Attribution without the & operator */ my_pointer = my_function; /* Dereferencing without the * operator */ int result = my_pointer(4, 2);
To increase the readability of function pointers, typedefs may be used.
typedef void (*Callback)(int a);
void some_function(Callback callback)
{
int a = 4;
callback(a);
}
Another readability trick is that the C standard allows one to simplify a function pointer in arguments like above (but not in variable declaration) to something that looks like a function prototype; thus the following can be equivalently used for function definitions and declarations:
void some_function(void callback(int))
{
int a = 4;
callback(a);
}
