Swift 字符串String的截取

1、截取第3个到倒数第2个之间的字符串，不包含第3个和倒数第2个

let string = "hello,world!"
let startIndex = string.index(string.startIndex,offsetBy: 4)
let endIndex = string.index(string.endIndex, offsetBy: -2)
let subString = string[startIndex..<endIndex]
print(subString)
//打印为 
// o,worl

也可以指定截取前面第3个到第7个之接的字符串，不包含第3个和第7个

let string = "hello,world!"
let startIndex = string.index(string.startIndex,offsetBy: 4)
let endIndex = string.index(string.startIndex,offsetBy: 7)
let subString = string[startIndex..<endIndex]
print(subString)
//打印
//o,w

2、截取指定下标的字符，下面案例为截取下标为6的字符

let string = "hello,world!"
let index = string.index(string.startIndex,offsetBy: 6)
let subString = string[index]
print(subString)
//打印为
//w

3、从字符串开头进行截取字符串，下面案例为截取前面5个字符串

let string = "hello,world!"
let prefix = string.prefix(5)
print(prefix)
//打印
//hello

3、从字符串末尾进行截取字符串，下面案例为截取后面6个字符串

let string = "hello,world!"
let suffix = string.suffix(6)
print(suffix)
//打印
//world!