I have a mapping in my smart contract with bytes32 keys and bytes values. How can I check if bytes value exists for specific key? Mapping is something like this:

mapping(bytes32 => bytes) public Countries;
  • ## This solution stands for bytes32: ``` Countries[_user] == "" // Returns true if Countries[_user] is not initialized ``` --- pragma solidity ^0.6.0; mapping(address => bytes32) public Countries; function isCountriesInitialized(address _user) external view returns (bool) { if (Countries[_user] == "") return false; return true; } --- I observe that on solidity v0.6.0 it may return 32 for length even though it is not mapped. Example of its returned value: b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
    – alper
    Commented Jan 6, 2020 at 13:30

1 Answer 1


You can check it via .length. It will be 0 if it is empty/uninitialised.

  • 2
    On solc v.0.6.0 this actually returns True, It sees b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' as length 32 @ivicaa
    – alper
    Commented Jan 6, 2020 at 11:39

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