working of pointer to functions in c

Question

Please look at the code following:-

 #include <stdio.h>
 int sum ( int b, int a){
 return (a+b);
  }
 int main(){
 int (* funptr)( int , int ) = sum;
 int a = ( * funptr )( 4,5);
 int b = funptr (4,5);
 printf("%d\n%d",a,b);
 return 1;
 }

Is there any difference between the two function calling via pointer,one is

int a = ( * funptr )( 4,5);

and another is

int b = funptr (4,5);

As i have compiled this code and result is same in both the cases.Is this means that these are equivalent?

They are identical, but personally I always use the (*funcptr)(...) form to make it explicit that I am dereferencing a pointer. Makes it clearer to the reader that it isn't a function with that actual name. — Dave
– Dave, Commented Mar 30, 2014 at 20:37
@Dave so dereferencing the function pointer yields the same value as without dereferencing? — OldSchool
– OldSchool, Commented Mar 30, 2014 at 20:39

deb_rider · Accepted Answer · 2014-03-30 20:40:50Z

2

In case of function pointer:

Function Pointer is very flexible to use.. You can put value into it with or without the & operator, and call the stored function through pointer with or without * operator.

e.g,

int (* funptr)( int , int ) = sum;   // or int (* funptr)( int , int ) = &sum;
int a = ( * funptr )( 4,5);          // or int a = funptr( 4,5);

Hope it helped...

answered Mar 30, 2014 at 20:40

deb_rider

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4 Comments

OldSchool Over a year ago

int (* funptr)( int , int ) = *sum; //or **sum is also equivalent?

deb_rider Over a year ago

Yes... You can put as many * as you want before sum it all will result same...

OldSchool Over a year ago

i have seen these statement written before few times what that mean by *sum as so what is the difference between sum and *sum and **sum?

deb_rider Over a year ago

if, as your previous example, sum is a function, and it is asked to differentiate sum and *sum, in this case actually *sum makes no sense, compiler just ignores the * operator in such case..

Deduplicator · Accepted Answer · 2014-03-30 20:45:20Z

2

Due to historic differences how to take the address of a function, you can apply address of and dereference any time you want to a function name, without any effect whatsoever.

Also, dereferencing a function pointer has no effect at all.

So, yes, your examples are equivalent.

edited Mar 30, 2014 at 20:45

answered Mar 30, 2014 at 20:35

Deduplicator

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8 Comments

OldSchool Over a year ago

so these two calling statements are equivalent?

Deduplicator Over a year ago

yes, they are equivalent. BTW: Get the standard: open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf

OldSchool Over a year ago

int (* funptr)( int , int ) = *sum; //or **sum is also equivalent?

Deduplicator Over a year ago

They are not equivalent to previous examples, but your two new examples are equivalent to each other...

OldSchool Over a year ago

oh! conflict between your and deb_rider comment please look at the comment of his answer.

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