ethereum - 如何在 Solidity 中比较 ascii 字符串和 uint8 数组？

Question

我有一个 uint8 数组，其中包含字符的 ASCII 码和一个字符串变量，我想对它们进行比较。例如:

uint8[3] memory foo = [98, 97, 122]; // baz
string memory bar = "baz";

bool result = keccak256(abi.encodePacked(foo)) == keccak256(abi.encodePacked(bytes(bar))); // false

这里我希望比较成功，但它失败了，因为 encodePacked 在编码时将保留数组中所有 uint8 元素的填充。

我该怎么做呢？

Answer 1

您当前正在将编码值 abi.encodePacked(foo)) 与散列值 keccak256(abi.encodePacked(bytes(bar)) 进行比较，两者永远不会相等。

---

uint8 固定大小数组存储在内存中的三个独立槽中 - 每个槽对应一个槽 - 每个槽都从右到左排序(小端)。

0x
0000000000000000000000000000000000000000000000000000000000000062
0000000000000000000000000000000000000000000000000000000000000061
000000000000000000000000000000000000000000000000000000000000007a

但是 string 文字存储为从左到右(大端)排序的动态大小字节数组:

0x
0000000000000000000000000000000000000000000000000000000000000020 # pointer
0000000000000000000000000000000000000000000000000000000000000003 # length
62617a0000000000000000000000000000000000000000000000000000000000 # value

因此，由于实际数据的存储方式不同，您无法对两个数组执行简单的字节比较。

但是，您可以遍历数组的所有项目并分别比较每个项目。

pragma solidity ^0.8;

contract MyContract {
    function compare() external pure returns (bool) {
        uint8[3] memory foo = [98, 97, 122]; // baz
        string memory bar = "baz";

        // typecast the `string` to `bytes` dynamic-length array
        // so that you can use its `.length` member property
        // and access its items individually (see `barBytes[i]` below, not possible with `bar[i]`)
        bytes memory barBytes = bytes(bar);

        // prevent accessing out-of-bounds index in the following loop
        // as well as false positive if `foo` contains just the beginning of `bar` but not the whole string
        if (foo.length != barBytes.length) {
            return false;
        }

        // loop through each item of `foo`
        for (uint i; i < foo.length; i++) {
            uint8 barItemDecimal = uint8(barBytes[i]);
            // and compare it to each decimal value of `bar` character
            if (foo[i] != barItemDecimal) {
                return false;
            }
        }

        // all items have equal values
        return true;
    }
}