我怎样才能得到字符串的第n个字符?我尝试了括号([])访问器，没有运气。
var string = "Hello, world!"
var firstChar = string[0] // Throws error
错误:'下标'是不可用的:不能下标String与Int，请参阅文档注释讨论
当前回答
斯威夫特3
extension String {
public func charAt(_ i: Int) -> Character {
return self[self.characters.index(self.startIndex, offsetBy: i)]
}
public subscript (i: Int) -> String {
return String(self.charAt(i) as Character)
}
public subscript (r: Range<Int>) -> String {
return substring(with: self.characters.index(self.startIndex, offsetBy: r.lowerBound)..<self.characters.index(self.startIndex, offsetBy: r.upperBound))
}
public subscript (r: CountableClosedRange<Int>) -> String {
return substring(with: self.characters.index(self.startIndex, offsetBy: r.lowerBound)..<self.characters.index(self.startIndex, offsetBy: r.upperBound))
}
}
使用
let str = "Hello World"
let sub = str[0...4]
有用的编程技巧和技巧(我写的)
其他回答
顺便说一句，有几个函数可以直接应用于String的字符链表示，像这样:
var string = "Hello, playground"
let firstCharacter = string.characters.first // returns "H"
let lastCharacter = string.characters.last // returns "d"
结果类型为Character，但可以将其转换为String。
或:
let reversedString = String(string.characters.reverse())
// returns "dnuorgyalp ,olleH"
:-)
Swift3
可以使用下标语法访问特定String索引处的Character。
let greeting = "Guten Tag!"
let index = greeting.index(greeting.startIndex, offsetBy: 7)
greeting[index] // a
访问https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html
或者我们可以在Swift 4中做一个字符串扩展
extension String {
func getCharAtIndex(_ index: Int) -> Character {
return self[self.index(self.startIndex, offsetBy: index)]
}
}
用法:
let foo = "ABC123"
foo.getCharAtIndex(2) //C
斯威夫特3
extension String {
public func charAt(_ i: Int) -> Character {
return self[self.characters.index(self.startIndex, offsetBy: i)]
}
public subscript (i: Int) -> String {
return String(self.charAt(i) as Character)
}
public subscript (r: Range<Int>) -> String {
return substring(with: self.characters.index(self.startIndex, offsetBy: r.lowerBound)..<self.characters.index(self.startIndex, offsetBy: r.upperBound))
}
public subscript (r: CountableClosedRange<Int>) -> String {
return substring(with: self.characters.index(self.startIndex, offsetBy: r.lowerBound)..<self.characters.index(self.startIndex, offsetBy: r.upperBound))
}
}
使用
let str = "Hello World"
let sub = str[0...4]
有用的编程技巧和技巧(我写的)
一个类似蟒蛇的解决方案，允许你使用负下标，
var str = "Hello world!"
str[-1] // "!"
可能是:
extension String {
subscript (var index:Int)->Character{
get {
let n = distance(self.startIndex, self.endIndex)
index %= n
if index < 0 { index += n }
return self[advance(startIndex, index)]
}
}
}
顺便说一下，调换整个python的切片符号可能是值得的
我也有同样的问题。简单地这样做:
var aString: String = "test"
var aChar:unichar = (aString as NSString).characterAtIndex(0)
