Writing a function pointer in c
c, function, function-pointers
Solution
int (*fn_pointer ( this_args ))( this_args );
declares `fn_pointer` as a function that takes `this_args` and returns a pointer to a function that takes `this_args` as argument and returns an `int` type. It is equivalent to
typedef int (*func_ptr)(this_args);
func_ptr fn_pointer(this_args);
Let's understand it a bit more:
int f1(arg1, arg2); // f1 is a function that takes two arguments of type
// arg1 and arg2 and returns an int.
int *f2(arg1, arg2); // f2 is a function that takes two arguments of type
// arg1 and arg2 and returns a pointer to int.
int (*fp)(arg1, arg2); // fp is a pointer to a function that takes two arguments of type
// arg1 and arg2 and returns a pointer to int.
int f3(arg3, int (*fp)(arg1, arg2)); // f3 is a function that takes two arguments of
// type arg3 and a pointer to a function that
// takes two arguments of type arg1 and arg2 and
// returns an int.
int (*f4(arg3))(arg1, arg2); // f4 is a function that takes an arguments of type
// arg3 and returns a pointer to a function that takes two
// arguments of type arg1 and arg2 and returns an int
How to read `int (*f4(arg3))(arg1, arg2);`
f4 -- f4
f3( ) -- is a function
f3(arg3) -- taking an arg3 argument
*f3(arg3) -- returning a pointer
(*f3(arg3))( ) -- to a function
(*f3(arg3))(arg1, arg2) -- taking arg1 and arg2 parameter
int (*f3(arg3))(arg1, arg2) -- and returning an int
So, finally a home work :). Try to figure out the declaration
void (*signal(int sig, void (*func)(int)))(int);
and use `typedef` to redefine it.
Problem
I was recently reading a code, and found that a function pointer is written as : ``` int (*fn_pointer ( this_args ))( this_args ) ``` I usually encounter a function pointer like this : ``` return_type (*fn_pointer ) (arguments); ``` Similar thing is discussed here: ``` // this is a function called functionFactory which receives parameter n // and returns a pointer to another function which receives two ints // and it returns another int int (*functionFactory(int n))(int, int) { printf("Got parameter %d", n); int (*functionPtr)(int,int) = &addInt; return functionPtr; } ``` Can somebody tell me what is the difference and how does this work ?