尝试从字符串中检索随机字母时出现分段错误

Question

我有这个功能：

func getRandomLetter() -> String {
    let len = allPossibleLetters.characters.count
    let r = arc4random_uniform(UInt32(len))
    let index = allPossibleLetters.index (allPossibleLetters.startIndex, offsetBy: r)
    return String(allPossibleLetters[index])
}

然而，我在尝试编译时不断收到以下错误：

Command failed due to signal: Segmentation fault: 11

当我将一个整数硬编码到 offsetBy 参数中时，它工作正常：

let index = allPossibleLetters.index (allPossibleLetters.startIndex, offsetBy: 11)
// returns a letter as expected

知道是什么原因造成的吗？

Answer 1

想通了。已更改

let r = arc4random_uniform(UInt32(len))

至

let r = Int(arc4random_uniform(UInt32(len)))

现在可以正常使用了。

Answer 2

似乎传递的类型有误：

let index = allPossibleLetters.index(allPossibleLetters.startIndex, offsetBy: Int(r))

对于那些分段问题，如果您单击该错误，它将带您到错误详细信息。通常这个日志的最后是最有趣的。在你的情况下它说：

While type-checking expression at RangeText="allPossibleLetters.index(allPossibleLetters.startIndex, offsetBy: r)"

尝试从字符串中检索随机字母时出现分段错误

Segmentation fault when trying to retrieve random letter from string

swift

string

swift3

segmentation-fault

arc4random