字符串

swift 字符串

一、创建空字符串

//-------------定义一个空字符串第一种方法
var str1=""

//-------------定义一个空字符串第二种方法
var  str2 = String()

二、判断字符串是否为空 （isEmpty)

//-----------判断字符串是否为空
var str3:String = ""

if str3.isEmpty { //isEmpty是字符串的一个属性，判断字符串是否为空
    print("str3的值是空")
}
else{
    print("str3的值不为空")
}

三、字符串的转义符

\0   空字符
\\    反斜杠
\t    制表符
\n   换行符
\r    回车符
\”    双引号
\’    单引号

四、字符串拼接

//-----------多个字符串变量拼接 用 + 来拼接

var  str4 = "hello"
var  str5 = " swift"
var  str6 = str4+str5 //字符串变量拼接
print("str6=\(str6)")


//-----------字符串变量和常量用+或 +＝来拼接
var  str7="hello "
str7 += "swift" //字符串变量和字符常量拼接可以用+＝ 拼接
print("str7=\(str7)")

五、字符串比较

var  strA = "Hello"
var  strB = "Hello"

//-----------字符串相等 == -------
if  strA == strB{
    print("字符串-相等")
}
else{
    print("字符串-不相等")
}
//-----------字符串前缀相等 hasPrefix---------
if strA.hasPrefix("H"){
    print("字符串前缀-相等")
}
else{
    print("字符串前缀-不相等")
}
//-----------字符串后缀相等 hasSuffix---------
if strA.hasSuffix("o"){
    print("字符串后缀-相等")
}
else{
    print("字符串后缀-不相等")
}

六、字符串 大小写转换

//-----------字符串大写转换
var  strB = strA.uppercased() //uppercaseString 字符串大写转换
print (strB)

//------------字符串小写转换
var strC = strA.lowercased() //lowercaseString 字符串转换小写
print(strC)

七、字符串遍历  (for in)

var str = "ABC"
/*
 1:str 是字符串变量 是字符集合
 2:temp是临时变量
 3:for in 会遍历 字符集合，然后把每个集合赋值临时变量temp
 
 */

for temp  in str.unicodeScalars {
    print(temp)
}

let str="mandarava"
for ch in str.characters{
    print(ch)
}

八、拆分字符串

 let str = "Apple,iOS,Swift,String"
let stringArray = str.components(separatedBy: ",")
for sub in stringArray{
    print(sub)
}

//含有多个不同的字符

let str1 = "Apple,iOS;Swift,String"
let stringArray = str1.components(separatedBy: CharacterSet.init(charactersIn: ",;"))
for sub in stringArray{
    print(sub)
}

九、字符串转换

let number = "100"
print(Int(number) ?? 0)

print((number as NSString).floatValue)
print((number as NSString).intValue)
print((number as NSString).integerValue)
print((number as NSString).longLongValue)
print((number as NSString).doubleValue)

var str3="true"
print((str3 as NSString).boolValue)

十、字符串长度

let str = "dsdsd"
let len1 = str.characters.count
print(len1)
let len2 = str.lengthOfBytes(using: String.Encoding.utf8)
print(len2)

十一、字符串包含

let str1="hello,mandarava."
let str2="mandarava"
let range=str1.range(of: str2)
if range != nil{
   print("包含")
}

十二、首字母大写

var str1="mandarava is a flower."
var sr = str1.capitalized
print(sr)

十三、根据位置获取字符串

let comment = "Hello,world!Welcome to Earth."
let  index = comment.index(comment.endIndex, offsetBy: -2)
print(comment.substring(from: index)) // h.

let  index1 = comment.index(comment.startIndex, offsetBy: 0)
print(comment.substring(from: index1)) //Hello,world!Welcome to Earth.

let  index2 = comment.index(comment.startIndex, offsetBy: 3)
print(comment.substring(to: index2)) //Hel

 

var a=NSString(string:"Follow your heart, but be quiet for a while first. Learn to trust your heart.")

print("截取前：\(a)")

print("截取后：\(a.substring(with: NSMakeRange(50, 8)))")

var a=NSString(string:"A,B,C,D,E,F")

print("分割前：\(a)")

print("分割后：\(a.components(separatedBy: ","))")                                 //分割字符串

运行结果如下：

分割前：A,B,C,D,E,F

分割后：["A", "B", "C", "D", "E", "F"]