How to initialize an empty array and push items into it?

Question

Here's my function:

function Test() constant returns (uint[]) {
   var myArray = uint[];
   myArray.push(123); 
   return myArray;
}

Here's an error I get in the solidity online compiler:

ballot.sol:25:9: Error: Member "push" not found or not visible after argument-dependent lookup in type(uint256[] memory) myArray.push(123);

score 66 · Accepted Answer · answered Jan 20 '17 at 08:45

66

You need to use an array in storage because it is not possible to resize memory arrays.

contract D { 
    uint[] myArray;
    function Test() constant returns (uint[]) {
       myArray.push(123); 
       return myArray;
    }
}

Otherwise you need to define the size of the array during initialization:

contract C {
    function f(uint len) {
        uint[] memory a = new uint[](7);
        bytes memory b = new bytes(len);
        // Here we have a.length == 7 and b.length == len
        a[6] = 8;
    }
}

answered Jan 20 '17 at 08:45

eth

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1

Oh, I get it now, thank you for your time and knowledge! – manidos Jan 20 '17 at 09:02
1

It was so simple I completely missed it – OneChillDude Sep 30 '17 at 06:36
6

If we need a memory array inside a function, but wen don't know the items count, what can we do? Thank you! – Suge Dec 24 '17 at 05:50
4

@Suge I suggest asking a separation question with more details and be careful to avoid https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem – eth Dec 30 '17 at 13:52

score 4 · Answer 2 · answered Mar 08 '22 at 19:49

4

You could define the array with the length of the array you want to filter. Problem is all the tail of empty elements.

uint[] memory filteredArray = new uint[](fullArray.length);
a[0] = 1;

answered Mar 08 '22 at 19:49

R01010010

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2
5

How to initialize an empty array and push items into it?

2 Answers2

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