Swift 获取字符串长度

• 字符串的长度获取，可以从以下几种情况理解
  • 字符长度（语义理解的长度）
  • 不同字符编码的长度
    • 字符串unicode长度
    • 字符串utf16长度
    • 字符串utf32长度(和unicode相等)
    • 字符串UTF-8长度

• 语义字符长度

    let cafe = "Cafe\u{301} du 🌍"  
    print(cafe)
    // Prints "Café du 🌍"  
    print(cafe.count)
    // Prints "9"
    print(Array(cafe))
    // Prints "["C", "a", "f", "é", " ", "d", "u", " ", "🌍"]"
  

  • 不同字符编码的长度
    - unicode字符长度

            print(cafe.utf16.count)
            // Prints "11"
            print(Array(cafe.utf16))
            // Prints "[67, 97, 102, 101, 769, 32, 100, 117, 32, 55356, 57101]"
    - utf16字符长度
    
            let nscafe = cafe as NSString
            print(nscafe.length)
            // Prints "11"
            print(nscafe.character(at: 3))
            // Prints "101"
    - UTF-8字符长度
    
            print(cafe.utf8.count)
            // Prints "14"
            print(Array(cafe.utf8))
            // Prints "[67, 97, 102, 101, 204, 129, 32, 100, 117, 32, 240, 159, 140, 141]"
    

• How to measuring the Length of a String

  • sample1：

      let capitalA = "A"
      print(capitalA.count)
      // Prints "1"
      print(capitalA.unicodeScalars.count)
      // Prints "1"
      print(capitalA.utf16.count)
      // Prints "1"
      print(capitalA.utf8.count)
      // Prints "1"
    

  • sample2：

      let flag = "🇵🇷"
      print(flag.count)
      // Prints "1"
      print(flag.unicodeScalars.count)
      // Prints "2"
      print(flag.utf16.count)
      // Prints "4"
      print(flag.utf8.count)
      // Prints "8"