How to push onto a dynamic sized Array within a function with Solidity?

Question

How can I push a value into an dynamic sized array within a function?

I have a function which builds an array dynamically to use this as a function argument afterwards:

function autoMintBatch(...) {
    uint32[] xList;
    uint32[] yList;

    // ... y is declared properly ...

    yList.push(y);

    for (uint256 i = 0; i < idList.length; i++) {
        xList.push(x++);
    }

}

I get the following compilation error:

TypeError: Member "push" is not available in uint32[] memory outside of storage.

But when I change the variable declaration to storage like:

uint32[] storage xList;

another error appears:

TypeError: This variable is of storage pointer type and can be accessed without prior assignment, which would lead to undefined behaviour.

Is there any way to build an array dynamically within a function?

Answer 1

Assign the result of "x++" in a variable inside the function and then try to push the variable inside the array. Remember to create a state variable for the array. This worked for me

Item[] public items;

event MarketItem(
    bytes32 title,
    uint8 price,
    bool sold,
    bool published,
    address owner
);

mapping(address => Item) public itemToOwner;

function addItem(bytes32 _title, uint8 _price) public {
    Item memory newItem = Item({
        title: _title,
        price: _price,
        sold: false,
        published: true,
        owner: msg.sender
    });
    items.push(newItem);
}