1.浮點類型的數(shù)字轉成String字符串
var f = 123.32342342
var s:String = "\(f)" //123.32342342
保留兩位小數(shù)
var f = 123.32342342
var s = String(format: "%.2f", f) //123.32
轉成十六進制格式字符串
let i = 255
let s:String = String(format: "%x", i) //ff
不足六位前面補0
let i = 255
let s:String = String(format: "%06x", i) //0000ff
