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)