Solidity – How to Initialize a uint16[] Array

arrayssolidity

I have a hard time creating a uint16[] array in an elegant way.

I try this:

function init() public {
uint16[] memory x = [uint16(1), uint16(1)];
test(x)
}

This raises TypeError: Type uint16[2] memory is not implicitly convertible to expected type uint16[]

I want to use this initialized array in a

function test(uint16[] input){}

function

I can of course create a uint16[] array and the push values in it, but this is not an elegant way of initializing it. How do I correctly initialize these values?

Best Answer

With the current version of Solidity (v.0.4.21), fixed size memory arrays cannot be assigned to dynamically-sized memory arrays.

Check out the documentation on Array Literals / Inline Arrays in the Solidity documentation.

The following code will not work:

// This will not compile.

pragma solidity ^0.4.0;

contract C {
    function f() public {
        // The next line creates a type error because uint[3] memory
        // cannot be converted to uint[] memory.
        uint[] x = [uint(1), 3, 4];
    }
}

The documentation says:

It is planned to remove this restriction in the future but currently creates some complications because of how arrays are passed in the ABI.

Related Solutions

How to Create a Mapping of Strings and Struct Arrays in Solidity

These are the basic patterns you need and you can base your more sophisticated getter/setter/remover functions on.

pragma solidity ^0.4.11;

contract AuthorizationManager{
    struct User{
      string userId;
      uint roleId;
    }

    mapping (string => User[]) companyUserMap;

    function addUser(string _key,string _userId, uint _roleId){
        companyUserMap[_key].push(User(_userId,_roleId));
    }

    function removeSingleUser(string _key){
        companyUserMap[_key].length--;
    }
}

Generally you should be really cautious when you iterate over large mappings, arrays etc. You could easily run out of gas and potentially lock your contract up. This is an instructive example.

Solidity – Initialize Memory Array of Fixed Size

To initialize an empty array instead of uint8[12] memory traits = new uint8[12]; use uint8[12] memory traits;.

Then you can alter the array in the // alter values in traits ... section.

function splitN(uint256 n) constant returns (uint8[12]) {
    uint8[12] memory traits;
    // alter values in traits ...
    return traits;
}

Best Answer

Related Solutions

How to Create a Mapping of Strings and Struct Arrays in Solidity

Solidity – Initialize Memory Array of Fixed Size

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