[Ethereum] How to return dynamic string array in Solidity

dappssoliditystring

How can I return a dynamic string array? I came across serialization and deserialization. How can I serialize and deserialize dynamic string array ?

pragma solidity ^0.5.0;

contract Abc{
    string[] st;

    function add(string memory newValue) public {
        st.push(newValue);
    }

    // return st

Best Answer

As of Solidity 0.7.5 the ABIEncoderV2 is not experimental anymore and can be selected using the pragma directive.

This gives native support for returning dynamic string arrays from functions.

pragma solidity ^0.8.2;
pragma abicoder v2;

contract Abc {
    string[] st;

    function add(string memory newValue) public {
        st.push(newValue);
    }

    function getSt() public view returns (string[] memory) {
        return st;
    }
}

On a side note, starting with Solidity 0.8.0 abicoder v2 is enabled by default and the pragma directive can therefore be omitted.

Related Solutions

[Ethereum] How to serialize an array of strings in Solidity

This is not going to work in Solidity. The += operator is not implemented for strings, you need to use a library that allows to concatenate strings; I think the most popular is this one. There is an example of how to use concatenation here.

I'm not sure what you're trying to do, but that kind of concatenation is expensive. Wouldn't it be enough to have two methods:

getStringsLength() returns (uint) and getStringByIndex(uint index) returns (string), and retrieve the strings in a loop? You can then do the concatenation outside of the contract (probably cheaper).

Solidity:

string[] myArray;

function getStringsLength() returns (uint) {
    return myArray.length;
}

function getStringByIndex(uint index) returns (string) {
    if (index < myArray.length){
        return myArray[index];
    }
    return "";
}

Solidity-consumer pseudocode:

strings_to_serialize = []
for (int i=0; i<contract.getStringsLength(); i++)
    strings_to_serialize.append(contract.getStringByIndex(i))
# process the strings here

[Ethereum] How to handle dynamic size string array in solidity

Solidity cannot return string arrays in current version. One workaround is to serialize the string array and then de-serialize it on client side.

An example :

https://hackernoon.com/serializing-string-arrays-in-solidity-db4b6037e520

Best Answer

Related Solutions

[Ethereum] How to serialize an array of strings in Solidity

[Ethereum] How to handle dynamic size string array in solidity

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