CODEWITHSUNDEEP
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gaotongfei
gaotongfei

Reputation: 353

What does the "48" mean in the code that converts uint to string in solidity

I found this code when I searched for ways to convert uint value into string. It's from OpenZeppelin: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/3dac7bbed7b4c0dbf504180c33e8ed8e350b93eb/contracts/utils/Strings.sol#L16-L36

function toString(uint256 value) internal pure returns (string memory) {
    // Inspired by OraclizeAPI's implementation - MIT licence
    // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

    if (value == 0) {
        return "0";
    }
    uint256 temp = value;
    uint256 digits;
    while (temp != 0) {
        digits++;
        temp /= 10;
    }
    bytes memory buffer = new bytes(digits);
    while (value != 0) {
        digits -= 1;
        buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
        value /= 10;
    }
    return string(buffer);
}

I can't understand what bytes1(uint8(48 + uint256(value % 10))) means, specifically what does the magic number 48 mean here. Appreciate it if someone can shed some light on it.

Upvotes: 1

Views: 333

Answers (1)

Joachim Isaksson
Joachim Isaksson

Reputation: 181047

48 is the ascii value for the character '0'.

The loop in question basically takes the value modulo 10 (that is, the least significant digit) and adds 48 to it, converting it to an ascii character. It then divides the number by 10 to do the same with the second least significant digit and so on.

As an example, if value is 437, the modulo leaves 7. That 7 is added to 48 to make 55 which is the ascii value for the character '7'. It then divides value by 10 to do the same with the number 43 to get the next character.

Upvotes: 4

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