What is the use of this kind of declaration?

Question

I came across this kind of a declaration.

typedef int (*func) (int,int,int);

What is the meaning and use of this?

Answer 1

It defines func as type for function which accepts 3 integers and returns integer.

This is helpful when you pass functions as callbacks or put function addresses into arrays or something like that.

Answer 2

It defines a type func which is a pointer to a function returning an int and taking 3 int arguments.

An example of using this would be:

typedef int (*func) (int, int, int);

int foo(int a, int b, int c) {
    return a + b * c;
}

...

// Declare a variable of type func and make it point to foo.
// Note that the "address of" operator (&) can be omitted when taking the
// address of a function.
func f = foo; 

// This will call foo with the arguments 2, 3, 4
f(2, 3, 4);

A more realistic scenario might be having a bunch of functions that have the same return type and taking the same type/number of arguments, and you want to call different functions based on the value of some variable. Instead of having a bunch of if-statements or a large switch/case you could place the function pointers in an array and use an index to call the appropriate function.

Answer 3

That's the typedef'd name. It reads as: func is a pointer to a function that takes three ints and returns an int.

You can see more on this link