Why the dereference operator is used with the void keyword while declaring a void pointer?

Question

Why the dereference operator is used with the void keyword while declaring a void pointer?

Debojit Acharjee 455

Why the indirection/dereference operator (*) is used with the "void" keyword while declaring a void pointer? But in case of any other type of pointers the operator can be used with the pointer name.

#include <stdio.h>

int main()
{
    int a = 1;
    int *a2_ptr = &a;
    void* a_ptr = &a;

    printf("Value of 'a' from void pointer is %d and int pointer is %d\n", *(int*)a_ptr, *a2_ptr); // Dereferencing of void pointer using type casting

    return 0;
}

In the above program, the integer pointer "a2_ptr" is declared using the * operator with the pointer name but in case of the void pointer, why the operator is used with the "void: keyword?

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Answer 1

Barry Schwarz 3,746

Because void and void* have different meanings. You use the one that matches what you are trying to define.

Barry Schwarz 3,746 Reputation points

2023-07-28T04:47:59.5033333+00:00

I should also point out that the * used in a pointer declaration is not the dereference operator any more than it is the multiplication operator.
RLWA32 49,636 Reputation points

2023-07-28T08:54:58.4666667+00:00

It's also worth noting that the asterisk in a pointer declaration binds to the variable and not the type.
Debojit Acharjee 455 Reputation points

2023-07-28T12:29:40.44+00:00
void means void data type and *void mean a void pointer data type? If yes, then why it's not written as *int a? Where 'a' is a pointer.

Why the following program doesn't work.

#include <stdio.h> int main() { int a; *int a_ptr; // This should be correct if *void a_ptr is correct a = 1; a_ptr = &a; printf("%d", a); return 0; }
Barry Schwarz 3,746 Reputation points

2023-07-28T14:18:12.5+00:00
Where do you invent this stuff. Nobody said *void would work. In fact, you are the only person to use that sequence of characters. In a declaration, the asterisk in front of the variable name specifies that the variable is a pointer. The asterisk cannot be in front of the type.

In a C statement or declaration, the space character is sometimes irrelevant. a=b+c and a = b + c have identical meanings. Similarly,

void*x, void* x, void *x, and void * x

have identical meanings. The same is true if you change the type from void to int.

Finally, void is not a data type like int or double. You cannot have an object of type void. void has two uses. In a function declaration, it specifies that the function does not return a value. In a pointer declaration, it specifies that the variable being declared points to an object whose type is not known. In this case, it is illegal to defreference such a pointer
Debojit Acharjee 455 Reputation points

2023-07-31T11:13:41.5333333+00:00

Barry Schwarz - I used it because in case of void pointers, the asterisk can be used with the "void" keyword but not with "int" keyword. Why is that?
Barry Schwarz 3,746 Reputation points

2023-07-31T15:26:54.6066667+00:00

What make you think an asterisk cannot be used with the type int? You used it yourself in the definition of a2_ptr. As noted above, the fact that you placed a space before the asterisk has no effect on the definition. You could have just as correctly placed the asterisk immediately after the word int. And a space after the asterisk is also optional.

Answer 2

Bruce (SqlWork.com) 78,086 Volunteer Moderator

The void* is used to declare an address pointer, where the type that the address points to is unknown.

Debojit Acharjee 455 Reputation points

2023-07-27T04:33:34.5733333+00:00

I know that but why the '*' operator is used with the "void" keyword but can't be used with the pointer name like an integer pointer (e.g. int *a).
Debojit Acharjee 455 Reputation points

2023-07-27T04:36:11.3466667+00:00

I know that, but why the '*' operator is used with the "void" keyword and can't be used with the pointer name like an integer pointer (e.g. int *a).
Minxin Yu 13,506 Reputation points Microsoft External Staff

2023-07-27T05:57:40.0366667+00:00

I consider the problem is with your compiler. You added the visual studio tag. Are you using visual studio and MSVC?
Debojit Acharjee 455 Reputation points

2023-07-28T12:18:02.37+00:00

Bruce (SqlWork.com) what you mean by "address pointer"? There is nothing like address pointer because every pointer stores an address. I think you didn't get my question. I want to know why the '*' operator is used with the "void" keyword instead of using it with the pointer name.
RLWA32 49,636 Reputation points

2023-07-28T12:31:00.49+00:00
@Debojit Acharjee The following two pointer declarations are equivalent.

void* pv; void *pv;

As I noted in a subsequent comment, the asterisk in a pointer declaration binds to the variable, not the type. In a declaration the asterisk indicates a pointer variable and is not interpreted by the compiler as a dereference operator.
Debojit Acharjee 455 Reputation points

2023-08-12T04:19:25.5266667+00:00

RLWA32 - thanks for the clarification.

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Why the dereference operator is used with the void keyword while declaring a void pointer?

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