字符串string的使用

1、定义可变字符串：

var str = "hello,swift"

2、定义不可变字符串：

let str = "hello world"

3、获取字符串的长度：

let count = str.characters.count

4、遍历字符串：

var str = "hello,swift"
for c in str.characters{
      print(c)
}

5、字符串拼接

两个字符串的拼接：

     let str1 = "shang"
     let str2 = "hai"
     let str3 = str1 + str2

字符串与其他数据类型的拼接：

     let name = "jay"
     let age = 12
     let info = "his name is \(name),age is \(age)."

字符串的截取

方式一：将string转成NSString

let str = "www.baidu.com"
var substr = (str as NSString).substringFromIndex(4)
substr =  (str as NSString).substringToIndex(3)
substr = (str as NSString).substringWithRange(NSRange(location:4,length:5))

方式二：swift截取

// 1.定义字符串
let str = "www.baidu.com"

// 2.截取开始位置
let fromIndex = str.startIndex.advancedBy(4)
let header = str.substringFromIndex(fromIndex)

// 3.截取结束位置
let toIndex = str.endIndex.advancedBy(-3)
let footer = str.substringToIndex(toIndex)

// 4.截取中间的字符串
let range = Range(start: str.startIndex.advancedBy(4), end: str.endIndex.advancedBy(-3))
let middle = str.substringWithRange(range)