Function Pointers Error In C [duplicate] - c

Question

This question already has answers here:
How do function pointers in C work?
(12 answers)
Closed 9 years ago.
In a book, I came across the following question.
The problem which I am facing is, what is a function pointer? How does it work and what is the syntax for it's declaration.
Point the error in given code.
main()
{
int (*p)()=fun;
(*p)();
}
fun()
{
printf("Hi..");
}
my first question is, What does following code snipet signifies?
int (*p)()=fun;
(*p)();
and second obvious question what is the error in the given code..??
refer to ionela.voinescu's answer for solution.. it is same as that written in solution manual..thnx

Answer 1

int (*p)() = fun declares a pointer to a function that returns int, then assigns the address of the function fun to that pointer. (*p)() calls whatever function p is pointing to.
Problems with your code:
fun and main should have a return type. Your compiler might not demand it and assume they return ints, but you should give them one nonetheless.
You need to declare fun above main, or use a prototype
Also, (*p)() is unnecessary; you can just use p().
As a side note, because function pointer syntax is relatively ugly, it's fairly common to see typedefs such as
typedef int(*IntFunc)();
which would allow you to declare and use p like so:
IntFunc p = fun;
p();

Answer 2

The correct code is the following:
#include <stdio.h>
int fun();
int main(){
int (*p)()=fun;
(*p)();
return 0;
}
int fun(){
printf("Hi..");
return 0;
}
1.
int fun();
You have to declare your function before using it in main; Otherwise main wont recognize it.
2.
int (*p)() : Declaration of a variable p which is a pointer to a function that returns int and has no arguments(or undefined number of arguments, depending on the standard).
3.
int fun();
.........
int (*p)()=fun;
In order for this to work fun must also return int. Meaning when assigning a value to a variable this must have a type which corresponds with the declaration of the variable. When assigning a value to a pointer to a function that returns int and has no arguments the function assigned to it must also return int and have no arguments (or undefined number of arguments, depending on the standard).
4.
(*p)();
You call the function p which now points to fun.

Answer 3

fun is name of the the function itself.
int (*p)()
is the definition of the function pointer like 'int a' is the definition of an integer.
int * is the pointer itself, () means it is a pointer to a function.
(*p)();
This is the execution of the function of the function pointer p, i.e. p is assigned to the function fun, which is executed by calling the content of the pointer p, thus (*p)();