Swift 字符串截取

截取前三个字符

 //方法一        
 let str = "0123456789"
 let subStr = str.prefix(3)
 print(subStr)//输出012

 //方法二
 let str = "0123456789"
 let endIndex =  str.index(str.startIndex, offsetBy: 3)
 let newStr = String(str[..<endIndex])
 print(newStr)//输出012

截取第三个到第六个范围内的字符

 let str = "0123456789"
 let startIndex = str.index(str.startIndex, offsetBy: 3)
 let endIndex =  str.index(str.startIndex, offsetBy: 6)
 let newStr = String(str[startIndex..<endIndex])
 print(newStr)//输出345

截取后三个字符

 //方法一
 let str = "0123456789"
 let subStr = str.suffix(3)
 print(subStr)//输出789
 
 //方法二
 let str = "0123456789"
 let startIndex =  str.index(str.endIndex, offsetBy: -3)
 let newStr = String(str[startIndex..<str.endIndex])
 print(newStr)