swift 3 get start index (as int) of substring

问题:

I would like to get the start and end position of a substring within a string. Example: in the string "hi this is my name"; if I provide the string "this" I would like to know the start index is 4 and end index is 7.

I found several links, including this one:

Swift: get index of start of a substring in a string a-substring-in-a-string

But it doesn´t work in swift 3 as the method is now called range.

I am now using this:

let range = mystring.range(of: "StringSearch")?.lowerBound

which returns this

Swift.String.UnicodeScalarView.Index(_position: 15), _countUTF16: 1))

And I cannot obtain the position as an integer as this is an index.

In summary, I would like to have in a variable of type int the position, in this case 15.

Can anyone help me?

Thanks everyone.

回答1:

The distance(from:to:) method of String computes the difference between two String.Index values:

let mystring = "hi this is my name"
if let range = mystring.range(of: "this") {
    let startPos = mystring.distance(from: mystring.startIndex, to: range.lowerBound)
    let endPos = mystring.distance(from: mystring.startIndex, to: range.upperBound)
    print(startPos, endPos) // 3 7
}

Actually it just forwards the call to the string's CharacterView, so the above gives the same result as

let mystring = "hi this is my name"
if let range = mystring.range(of: "this") {
    let startPos = mystring.characters.distance(from: mystring.characters.startIndex, to: range.lowerBound)
    let endPos = mystring.characters.distance(from: mystring.characters.startIndex, to: range.upperBound)
    print(startPos, endPos) // 3 7
}

---

If you need all occurrences of the string:

let mystring = "this is this and that is that"
var searchPosition = mystring.startIndex
while let range = mystring.range(of: "this", range: searchPosition..<mystring.endIndex) {
    let startPos = mystring.distance(from: mystring.startIndex, to: range.lowerBound)
    let endPos = mystring.distance(from: mystring.startIndex, to: range.upperBound)
    print(startPos, endPos)

    searchPosition = range.upperBound
}

回答2:

Adapted answer from Martin R into a function gives you the first occurrence as an NSRange. You could turn this into an extension of String also.

public class func indexOf(string: String, substring: String) -> NSRange? {
    if let range = string.range(of: substring) {
        let startPos = string.distance(from: string.startIndex, to: range.lowerBound)
        return NSMakeRange(startPos, substring.count)
    }
}