Two-dimensional arrays

Question

I believe it's possible to create a two-dimensional array according to this answer.

I am trying to create a two-dimensional array to store the address and ether of each incoming transaction.

Are two-dimensional arrays the best solution in this case? Do we have to set a length limit or can we make it infinitely long? How can we prevent malicious users from flooding the array?

Answer 1

When declaring a two-dimensional array in storage you are creating in reality nested arrays. And you do not need to declare sizes.

pragma solidity ^0.4.18;

contract C {

    // data[n] is an array of uints
    uint[][] data;

    function append(uint _a, uint _b) public {
        data.push([_a, _b]);
    }

    function read(uint _idx) public view returns (uint[]) {
        return data[_idx];
    }
}

Without more details about your problem is hard to recommend a particular solution.

• Arrays are more complex than mappings and can be slightly more expensive to use when adding a new element.

• Deleting a single element in an array does not resize the array, and you will need to find out how to deal with such situations.

• You can iterate an array but not a mapping. Also iterating a large array can cause out of gas errors.