Substring in solidity

Question

I am looking for a way to get substring of a String. I am looking for an equivalent of this Java method. I am ok to use libraries but did not find it in solidity-stringutils.

public String substring(int startIndex, int endIndex)

score 12 · Accepted Answer · answered Nov 23 '17 at 21:55

The solidity documentation states, that there is no built in string manipulation available. Nevertheless, we can convert a string to a byte array and do the manipulation manually:

function substring(string str, uint startIndex, uint endIndex) constant returns (string) {
    bytes memory strBytes = bytes(str);
    bytes memory result = new bytes(endIndex-startIndex);
    for(uint i = startIndex; i < endIndex; i++) {
        result[i-startIndex] = strBytes[i];
    }
    return string(result);
}

Disclaimer: this method works for ASCII strings, but not for characters that are encoded with multiple bytes in UTF-8 (e.g. umlaute).

Here's a fiddle so you can play around with it: https://ethfiddle.com/-IaBg6dld7 — James Duffy, Nov 24 '17 at 09:30
Thank you, Nicci and James for making the community better. I was not aware of ethfiddle. Very helpful. — Titu, Nov 24 '17 at 16:16

score 6 · Answer 2 · answered Mar 11 '22 at 19:17

Update for Solidity 0.8.0 versions

function substring(string memory str, uint startIndex, uint endIndex) public pure returns (string memory ) {
    bytes memory strBytes = bytes(str);
    bytes memory result = new bytes(endIndex-startIndex);
    for(uint i = startIndex; i < endIndex; i++) {
        result[i-startIndex] = strBytes[i];
    }
    return string(result);
}

score 0 · Answer 3 · answered Apr 01 '23 at 09:17

Here's a shorter, gas-efficient answer without for loops:

function trim(string calldata str, uint start, uint end) external pure returns(string memory) {
    return str[start:end];
}

This takes a string and start and end positions and returns a substring.

Substring in solidity

3 Answers3

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