swift-字符和字符串

• OC定义字符：

  char charValue = 'a';

• swift定义字符：

  var charValue : Character = "a"

• Unicode 国际标准的文本编码，他几乎可以表示所有国家的字符、
  OC可以存储ASCII字符，swift可以存ASCII+Unicode

  var charValue :Character = "🐶" //正确的
  var charValue2:Character = "小玉" //正确的
  var charValue3:Character = "玉" //错误的

  字符串是可以存很多字符的集合。
  OC:NSString * stringValue = @"小玉";
  swift:let stringValue:String = "小玉"

  区别：NSString/String @""/""

  //String -> NSString
  let string:NSString = NSString(string: "dahuan")

  OC是以‘\0’为字符串结束：NSString * stringValue = @"aaaa\0bbbb";
  swift不是以'\0'结束：let stringValue:String = "aaaa\0bbbb"

• 字符串的常用方法

  • 1、初始化空字符串

    let emptyString = ""
    let emptyString2 = String()

  • 2、遍历字符串

    let string2 = "康姐是我们的好朋友！"
    for a in string2.characters {
    print(a)
    }

  • 3、获取字符串的长度

    let count = string2.characters.count
    print(count)

  • 4、判断字符串是否为空

    let emptyStr = "1"
    if emptyStr.isEmpty {
    print("yes")
    }

  • 5、字符串的拼接

    let str1 = "康姐"
    let str2 = "是我们的好朋友！"
    let result = str1 + str2

    var str3 = "haha"
    str3 = str3 + str2
    print(str3)

  • 6、格式化字符串

    let intValue = 10
    let str4 = "爱情"
    let str5 = "(intValue)、因为(str4)，不会悲伤"
    print(str5)

    //取小数后两位
    let pi = 3.1415
    let str6 = String(format: "%.2f", pi)
    print(str6)

  • 7、字符串比较

    //和C语言strcmp一样

    let str7 = "a"
    let str8 = "ab"

    if str7 > str8 {
    print(">")
    } else if str7 < str8 {
    print("<")
    }

  • 8、是否有前后缀

    let str9 = "www.baidu.com"
    if str9.hasPrefix("www") {
    print("yes")
    } else {
    print("no")
    }
    if str9.hasSuffix("cm") {
    print("yes")
    } else {
    print("no")
    }

  • 9、大小写

    let str10 = str9.uppercaseString
    let str11 = str9.lowercaseString

    print(str10)

  • 10、String转基本数据类型

    let str12 = "5.2吗"
    let num = Float(str12)
    print(num)

  • 11、截取字符串

    let str13 = "康姐是我们的好朋友！"
    //str13.startIndex 从0开始 Index不是int
    let fromStr = str13.startIndex.advancedBy(2)
    let toStr = str13.endIndex.advancedBy(-2)
    let str14 = str13.substringFromIndex(toStr)

    let range:Range <String.Index> = Range(start: fromStr, end: toStr)
    let str15 = str13.substringWithRange(range)

    print(str15)

    let toStr1 = (str13 as NSString).substringToIndex(2);
    print(toStr1)

    let range1 = NSRange(location: 2, length: 6)

    let toStr2 = (str13 as NSString).substringWithRange(range1)
    print(toStr2)