rog rog - 1 month ago 14
Swift Question

swift 3 get start index (as int) of substring

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.

Answer

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
}