Swift - 将String类型的数字转换成数字类型（支持十进制、十六进制）

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//将文本框中的值转换成数字

var i = (tf1.text as NSString).intValue

var f = (tf1.text as NSString).floatValue

var d = (tf1.text as NSString).doubleValue

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func hexStringToInt(from:String) -> Int {

    let str = from.uppercased()

    var sum = 0

    for i in str.utf8 {

        sum = sum * 16 + Int(i) - 48 // 0-9 从48开始

        if i >= 65 {                 // A-Z 从65开始，但有初始值10，所以应该是减去55

            sum -= 7

        }

    }

    return sum

}

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let str = "FF0000"

let value = hexStringToInt(from:str)

print(value)

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extension String{

    func hexStringToInt() -> Int {

        let str = self.uppercased()

        var sum = 0

        for i in str.utf8 {

            sum = sum * 16 + Int(i) - 48 // 0-9 从48开始

            if i >= 65 {                 // A-Z 从65开始，但有初始值10，所以应该是减去55

                sum -= 7

            }

        }

        return sum

    }

}

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let str = "FF0000"

let value = str.hexStringToInt()

print(value)