What would the default value be for an uninitialized entry in the below mapping?

i.e. how to check if an address exists in the below mapping?

mapping (address => mapping (bytes32 => uint256)) public someNestedMapping;

1 Answer 1


Default for uninitialized storage slots (by the size of 32 bytes, aka a word) is always the 32 bytes of zeroes.

So to test if an address is part of the mapping you would check if

someNestedMapping[yourAddress][yourBytes32] == 0

  • Great - that helps a lot - thanks Richard.
    – simbro
    Dec 23, 2021 at 11:44

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