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)