用SWIFT編程語言獲取字符串的第n個字符我怎樣才能得到字符串的第n個字符？我試過支架([])沒有運氣的訪問者。var string = "Hello, world!"var firstChar = string[0] // Throws error錯誤：“下標”不可用：不能用Int下標字符串，有關討論，請參閱文檔注釋
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TA貢獻1836條經驗 獲得超13個贊
注意：
SWIFT 4
Substring
試試看 這里
extension String {
subscript (i: Int) -> Character {
return self[index(startIndex, offsetBy: i)]
}
subscript (bounds: CountableRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start ..< end]
}
subscript (bounds: CountableClosedRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start ... end]
}
subscript (bounds: CountablePartialRangeFrom<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(endIndex, offsetBy: -1)
return self[start ... end]
}
subscript (bounds: PartialRangeThrough<Int>) -> Substring {
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[startIndex ... end]
}
subscript (bounds: PartialRangeUpTo<Int>) -> Substring {
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[startIndex ..< end]
}}extension Substring {
subscript (i: Int) -> Character {
return self[index(startIndex, offsetBy: i)]
}
subscript (bounds: CountableRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start ..< end]
}
subscript (bounds: CountableClosedRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start ... end]
}
subscript (bounds: CountablePartialRangeFrom<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(endIndex, offsetBy: -1)
return self[start ... end]
}
subscript (bounds: PartialRangeThrough<Int>) -> Substring {
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[startIndex ... end]
}
subscript (bounds: PartialRangeUpTo<Int>) -> Substring {
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[startIndex ..< end]
}}SubstringStringString(string[0..2])Substring.
StringProtocolindex
SWIFT 3：
extension String {
subscript (i: Int) -> Character {
return self[index(startIndex, offsetBy: i)]
}
subscript (i: Int) -> String {
return String(self[i] as Character)
}
subscript (r: Range<Int>) -> String {
let start = index(startIndex, offsetBy: r.lowerBound)
let end = index(startIndex, offsetBy: r.upperBound)
return self[Range(start ..< end)]
}}
為什么這不是內置的？
帶有整數的子腳本字符串不可用。
“ i字符串中的TH字符在不同的庫和系統組件中有不同的解釋。正確的解釋應該根據用例和所涉及的api選擇，所以 String不能用整數訂閱。
SWIFT提供了幾種訪問字符串中存儲的字符數據的不同方法。
String.utf8是字符串中UTF-8代碼單元的集合。將字符串轉換為UTF-8時使用此API。大多數POSIX API以UTF-8代碼單元處理字符串。
String.utf16是字符串中UTF-16代碼單元的集合。大多數Cocoa和CocoaTouch API根據UTF-16代碼單元處理字符串。例如， NSRange與.連用 NSAttributedString和 NSRegularExpression以UTF-16碼單元存儲子字符串偏移量和長度。
String.unicodeScalars是Unicode標量的集合。當您執行字符數據的低級別操作時，請使用此API。
String.characters是一組擴展的字素聚類，它是用戶感知字符的近似。
請注意，在處理包含可讀的文本的字符串時，應盡可能避免逐字符處理。例如，使用高級別的對地區敏感的Unicode算法， String.localizedStandardCompare(),String.localizedLowercaseString,String.localizedStandardRangeOfString()等。
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