how to convert Hex String to ASCII String in KOTLIN

Question

I receive on my application with a BLE module a hexagonal String Hex string

0031302D31300D0A

This string in ASCII is 10-10\r\n (which represents the coordinates of the x axis and the y axis). I tried to use the toCharArray function to convert to ASCII in an array and have the possibility to parse the string and get the x and y values but it returns a string like this in the logcat [C@3cea859

I also tried to create a function but it returns the same type of string

fun String.decodeHex(): ByteArray{
        check(length % 2 == 0){"Must have an even length"}
        return chunked(2)
            .map { it.toInt(16).toByte() }
            .toByteArray()
    }

String hex = "0031302D31300D0A"; Please tell what x and y would be. String xhex = ... String yhex = .... — blackapps
– blackapps, Commented Mar 30, 2022 at 8:24
@blackapps xhex = 3130, separatorHex = 2D, yhex = 3130 endCharacHex = 0D0A — P.C
– P.C, Commented Mar 30, 2022 at 8:44
You mean xhex = "3130". A string. If you dont have a string at start (like i used in my comment) but a byte array of 8 bytes then please state so in your post. — blackapps
– blackapps, Commented Mar 30, 2022 at 10:22
yes @blackapps i mean xhex = "3130", separatorHex = "2D", yhex = "3130" endCharacHex = "0D0A" — P.C
– P.C, Commented Mar 30, 2022 at 11:48

k314159 · Accepted Answer · 2022-12-06 09:30:53Z

2

You're nearly there. You just need to convert the ByteArray to a String. The standard toString() method comes from type Any (equivalent to Java's Object). The ByteArray doesn't override it to give you what you want. Instead, use the String constructor or the toString(Charset) function:

fun String.decodeHex(): String {
    require(length % 2 == 0) {"Must have an even length"}
    return chunked(2)
        .map { it.toInt(16).toByte() }
        .toByteArray()
        .toString(Charsets.ISO_8859_1)  // Or whichever encoding your input uses
}

(Note also that require is more appropriate than check in that context.)

edited Dec 6, 2022 at 9:30

answered Mar 30, 2022 at 8:16

k314159

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13 Comments

P.C Over a year ago

Hey, I convert the byte array to a string with the toString function and get nothing on logcat.

fun String.decodeHex(): String{         require(length % 2 == 0){"Must have an even length"}         return String(chunked(2)             .map { it.toInt(16).toByte() }             .toByteArray())     }

// output : nothing

k314159 Over a year ago

Are you actually calling it? Something like log(hexString.decodeHex())?

k314159 Over a year ago

@P.C You can see it working here: pl.kotl.in/xMdOUuqfG

k314159 Over a year ago

@P.C one possible issue is that the string starts with hex 00 which results in a '\0' character at the beginning of the string, which maybe the logger doesn't like.

P.C Over a year ago

Yes i call it Log.i("sensor", hexstring.decodHex()) and the only thing I have is this 2022-03-30 11:22:56.397 2016-2016/com.example.lightrdetect D/sensor:

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