Swift 字符串截取

1. 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[..

2. 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..

3. 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..