[Solidity] Summary of default values (initial values) for mapping

The following is a summary of the default values (initial values) for mapping in Solidity.

The default values for mappings depend on the data type of the values set for the mapping.

They are explained in detail below.

Default value for mapping per value data type

The “data type of the value” refers to the bold marker here.

mapping (key datatype => value datatype) access qualifier variable name;

As mentioned at the beginning of this text, the default values for mapping are different for each value data type.

The following is a list of them.

Value Datatype	Default Value
uint, int	0
bool	false
address	address(0)（0x0000000000000000000000000000000000000000）
bytes	0x
string	""（empty string）

Sample Code

I have created a function that returns a default value for each data type.

Please run and check it.

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract Test {

    mapping (address => uint) public uintMapping;
    mapping (address => int) public intMapping;
    mapping (address => bool) public boolMapping;
    mapping (address => address) public addressMapping;
    mapping (address => bytes) public bytesMapping;
    mapping (address => string) public stringMapping;

    function getDefaultValueUint() public view returns (uint) {
        return uintMapping[msg.sender];
    }

    function getDefaultValueInt() public view returns (int) {
        return intMapping[msg.sender];
    }

    function getDefaultValueBool() public view returns (bool) {
        return boolMapping[msg.sender];
    }

    function getDefaultValueAddress() public view returns (address) {
        return addressMapping[msg.sender];
    }

    function getDefaultValueBytes() public view returns (bytes memory) {
        return bytesMapping[msg.sender];
    }
    
    function getDefaultValueString() public view returns (string memory) {
        return stringMapping[msg.sender];
    }

}