What is the correct way to check if an address is zero?

Question

I remember reading that the correct way to check if an address is 0x0 or not is _addr == address(0) and not _addr == 0. However, I'm unable to find any difference between the two when I run the following:

pragma solidity ^0.4.19;

contract Test {
    bool public isResult1 = false;
    bool public isResult2 = false;

    function isAddressZero1(address _addr) public {
        isResult1 = (_addr == address(0));
    }

    function isAddressZero2(address _addr) public {
        isResult2 = (_addr == 0);
    }
}

Is there a known issue with _addr == 0 or is the explicit typecasting just to be safe?

Any of those are fine. I usually do _addr != 0x0 to make it easily identifiable in code. — Adam Kipnis, Dec 29 '17 at 17:03

score 13 · Accepted Answer · edited Oct 31 '20 at 08:41

13

These should be completely equivalent. I think some people may prefer 0x0 or address(0) or address(0x0) as some sort of convention (to make it a little clearer what kind of 0 you mean), but they all should compile to the same thing.

Solidity Version 0.5.0 onwards, you cannot compare directly with 0 or 0x0 or "0" or "0x0". Since these types are not treated as address.

edited Oct 31 '20 at 08:41

Ashutosh Singh

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answered Dec 29 '17 at 17:22

user19510

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In Solidity version 0.5.0 ; comparing with integer 0 is not allowed anymore. – Stef Heyenrath Dec 08 '18 at 11:26

score 6 · Answer 2 · edited Mar 11 '19 at 14:19

6

In solidity 0.5 this is the correct way to compare addresses

require(address(_registry) != address(0));

edited Mar 11 '19 at 14:19

Rosco Kalis

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answered Mar 11 '19 at 13:12

Shahzad Aslam

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Any source to assert this is the correct way ? – Nicolas Massart Mar 11 '19 at 15:42
1

For instance these snippets from the solidity documentation? https://solidity.readthedocs.io/en/v0.5.3/solidity-by-example.html?highlight=address(0) – Briomkez Mar 19 '19 at 15:13

What is the correct way to check if an address is zero?

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