一段sol代码。求解释 | 登链社区

5 一段sol代码。求解释

function boxURL(uint boxID_) public view returns (string memory) { require(boxMap[boxID_].id != 0, "box not exist"); return string(abi.encodePacked(baseURL, boxID_)); }

看了一个别人的合约。这里为啥要用encodePacked呢？时什么作用。我调用合约返回的后面部分是乱码字符。不能直接拼接String吗？

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分类：以太坊

最佳答案 2022-09-05 09:48

baseURL = "http://192.168.1.1/" boxID_ = 1

abi.encodePacked(baseURL, boxID_) 结果为：0x687474703a2f2f3139322e3136382e312e312f0000000000000000000000000000000000000000000000000000000000000001 0x687474703a2f2f3139322e3136382e312e312f是"http://192.168.1.1/"的编码 0000000000000000000000000000000000000000000000000000000000000001是uint256(1)的编码这种情况下，是先分别编码再拼接

而 abi.encodePacked(baseURL, Strings.toString(boxID_) 结果为： 0x687474703a2f2f3139322e3136382e312e312f31 ”http://192.168.1.1/1“的编码这种情况下，是先拼接再编码

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Meta - 风是自由的，你也是

采纳率 22% | 回答于 2022-09-03 19:09

默认排序时间排序

其它 3 个回答

zen 2022-09-02 12:44

```
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

/**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    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);
    }

/**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

/**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}
```
用库转下int,再encodePacked

solidity开发 - solidity开发工程师 2022-09-02 14:20

午时已到 2022-09-02 18:22