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[Swift]浮動小数点⇔文字列の変換

以外と時間がかかったのでメモ。

  • Double型などの浮動小数点数値と文字列の相互変換は、String型では定義されていないため、NSString型を用いる必要がある

String --> Double(Float,Int,Int64,etc)

swift
let str: String = "3.3"

var dNum: Double = NSString(string: str).doubleValue   // 3.3
var fNum: Float  = NSString(string: str).floatValue    // 3.2999....
var iNum: Int    = NSString(string: str).integerValue  // 3
var lNum: Int64  = NSString(string: str).longLongValue // 3
var bNum: Bool   = NSString(string: str).boolValue     // true      

Double --> String

swift
let num = 3.33

var strf: String = NSString(format: "%.2f", num)
var strF: String = NSString(format: "%.2F", num)
var stre: String = NSString(format: "%.2e", num)
var strE: String = NSString(format: "%.2E", num)
var strg: String = NSString(format: "%.2g", num)
var strG: String = NSString(format: "%.2G", num)

参考

  • 整数Int⇔文字列Stringの相互変換は、String型にて定義されている

Int --> String

swift
let num: Int = 3
var str: String = String(num)

String --> Int

swift
let str: String = "3"
var num: Int? = str.toInt()

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