Why &(&i)is not valid in C?

Question

#include <stdio.h>
int main()
{
int i;
i=0;
printf("%d\n%d\n%d\n", i, &i, &(&i));
return 0;
}

i think that &i is just a value of address, and assume that it's 0xFF so &(&i)should be the address of 0xFF but why it's not valid?

..because it makes less sense than Mourinho taking over at Man U. — Martin James, May 22 '16 at 17:27
I meant that 0xFF is also a constant, so there should be a constant that refers to the address of the constant '0xFF' — Woonsung Baek, May 22 '16 at 18:19

haccks · Accepted Answer · 2016-05-22T16:06:47.467

7

Unary & operator need an lvalue as its operand and returns an rvalue. &i is an rvalue, therefore &i can't be an operand of &.

edited May 22 '16 at 16:06

answered May 22 '16 at 15:51

haccks

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Would address of a variable considered as constant ? – ameyCU May 22 '16 at 16:15
@ameyCU; Yes, it is. – haccks May 22 '16 at 16:15
Thnx a lot! I got it perfectly! – Woonsung Baek May 22 '16 at 18:22

score 2 · Answer 2 · edited Jun 20 '20 at 09:12

6.5.3.2.

The operand of the unary & operator shall be either a function designator, the result of a [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is not declared with the register storage-class specifier.

&i is an address of an object.

This means that unary &cannot be used on &i, as the address doesn't designate an object or a function, nor is the result of [] or * operator.

Your example is effectively: &0, and constant 0 obviously doesn't fall on the above list.

score 1 · Answer 3 · answered May 22 '16 at 16:34

1

Don't confuse addresses and pointers.An address is an rvalue.You can't apply the "address of"(&) operator on it.Pointers however are objects.They are lvalue-s and can be the operand of '&'.

answered May 22 '16 at 16:34

machine_1

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score 0 · Answer 4 · answered May 22 '16 at 19:31

Easy, look at it this way. You got a bee nest. In a square I put some honey. Using the & operator you refer to that square. Using again the & operator you refer to the square in which the square is located, you can`t do that.

More precisely &i refer to the memory location is i. You can`t refer to the memory location of a memory location.

Why &(&i)is not valid in C?

4 Answers4