我想将字符串中包含的字母的索引转换为整数值.尝试读取头文件,但我找不到索引的类型,虽然它似乎符合协议ForwardIndexType与方法(例如distanceTo).
var letters = "abcdefg" let index = letters.characters.indexOf("c")! // ERROR: Cannot invoke initializer for type 'Int' with an argument list of type '(String.CharacterView.Index)' let intValue = Int(index) // I want the integer value of the index (e.g. 2)
任何帮助表示赞赏.
您需要使用与原始字符串起始索引相关的distanceTo(index)方法:
let intValue = letters.startIndex.distanceTo(index)
您还可以使用方法扩展String以返回字符串中第一次出现的字符,如下所示:
extension String { func indexDistanceOfFirst(character character: Character) -> Int? { guard let index = characters.indexOf(character) else { return nil } return startIndex.distanceTo(index) } } let letters = "abcdefg" let char: Character = "c" if let index = letters.indexDistanceOfFirst(character: char) { print("character \(char) was found at position #\(index)") // "character c was found at position #2\n" } else { print("character \(char) was not found") }
Xcode 8•Swift 3
let letters = "abcdefg" if let index = letters.characters.index(of: "c") { let distance = letters.distance(from: letters.startIndex,to: index) print("distance:",distance) }
extension String { func indexDistance(of character: Character) -> Int? { guard let index = characters.index(of: character) else { return nil } return distance(from: startIndex,to: index) } }
let letters = "abcdefg" let char: Character = "c" if let index = letters.indexDistance(of: char) { print("character \(char) was found at position #\(index)") // "character c was found at position #2\n" } else { print("character \(char) was not found") }
Xcode 9•Swift 4
let letters = "abcdefg" if let index = letters.index(of: "c") { let distance = letters.distance(from: letters.startIndex,distance) }
extension String { func indexDistance(of character: Character) -> Int? { guard let index = index(of: character) else { return nil } return distance(from: startIndex,to: index) } }
Swift 4中另一种可能的方法是返回index encodedOffset:
extension String { func encodedOffset(of character: Character) -> Int? { return index(of: character)?.encodedOffset } func encodedOffset(of string: String) -> Int? { return range(of: string)?.lowerBound.encodedOffset } }
let letters = "abcdefg" let char: Character = "c" if let index = letters.encodedOffset(of: char) { print("character \(char) was found at position #\(index)") // "character c was found at position #2\n" } else { print("character \(char) was not found") }