当源包含 unicode 字符时，Swift 正则表达式匹配失败 [英] Swift Regex matching fails when source contains unicode characters

问题描述

我正在尝试使用 NSRegularExpression 进行简单的正则表达式匹配，但是当源包含多字节字符时，我在匹配字符串时遇到了一些问题:

I'm trying to do a simple regex match using NSRegularExpression, but I'm having some problems matching the string when the source contains multibyte characters:

let string = "D 9"

// The following matches (any characters)(SPACE)(numbers)(any characters)
let pattern = "([\\s\\S]*) ([0-9]*)(.*)"

let slen : Int = string.lengthOfBytesUsingEncoding(NSUTF8StringEncoding)

var error: NSError? = nil

var regex = NSRegularExpression(pattern: pattern, options: NSRegularExpressionOptions.DotMatchesLineSeparators, error: &error)

var result = regex?.stringByReplacingMatchesInString(string, options: nil, range: NSRange(location:0,
length:slen), withTemplate: "First \"$1\" Second: \"$2\"")

上面的代码按预期返回D"和9"

The code above returns "D" and "9" as expected

如果我现在将第一行更改为包含英国英镑"货币符号，如下所示:

If I now change the first line to include a UK 'Pound' currency symbol as follows:

let string = "£ 9"

然后匹配不起作用，即使表达式的 ([\\s\\S]*) 部分仍应匹配 任何 前导字符.

Then the match doesn't work, even though the ([\\s\\S]*) part of the expression should still match any leading characters.

我知道 £ 符号将占用两个字节，但通配符前导匹配应该忽略那些不应该吗?

I understand that the £ symbol will take two bytes but the wildcard leading match should ignore those shouldn't it?

谁能解释一下这里发生了什么?

Can anyone explain what is going on here please?

推荐答案

这可能会令人困惑.stringByReplacingMatchesInString() 的第一个参数是从 NSString 中映射而来的Objective-C 在 Swift 中转为 String，但 range: 参数仍然是NSRange.因此，您必须以单位指定范围NSString 使用的(这是 UTF-16 代码点的数量):

It can be confusing. The first parameter of stringByReplacingMatchesInString() is mapped from NSString in Objective-C to String in Swift, but the range: parameter is still an NSRange. Therefore you have to specify the range in the units used by NSString (which is the number of UTF-16 code points):

var result = regex?.stringByReplacingMatchesInString(string,
        options: nil,
        range: NSRange(location:0, length:(string as NSString).length),
        withTemplate: "First \"$1\" Second: \"$2\"")

或者你可以使用 count(string.utf16)而不是 (string as NSString).length .

Alternatively you can use count(string.utf16) instead of (string as NSString).length .

完整示例:

let string = "£ 9"

let pattern = "([\\s\\S]*) ([0-9]*)(.*)"
var error: NSError? = nil
let regex = NSRegularExpression(pattern: pattern,
        options: NSRegularExpressionOptions.DotMatchesLineSeparators,
        error: &error)!

let result = regex.stringByReplacingMatchesInString(string,
    options: nil,
    range: NSRange(location:0, length:(string as NSString).length),
    withTemplate: "First \"$1\" Second: \"$2\"")
println(result)
// First "£" Second: "9"

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