difference between FileHandle in Swift 3.0 and FileInputStream in java

Question

in java I use this code too read mp3 file in to buffer

byte[] buffer = new byte[12];
stream.read(buffer, offset, 12 - offset); 
for(int i = 0; i<buffer.length ; i++){
     Log.e("buff","buff "+ buffer[i]);
}

and here's result of buffer

69 82 0 0 0 5 0 0 0 -50 -76 -42

in swift 3.0

var buffer = Data()
let file = try FileHandle(forReadingFrom: urlLocal)
file.seek(toFileOffset: 0)
buffer = file.readData(ofLength: 12)
for  i in  0...(buffer.count-1){
            print(buffer[i])
}

and here is result of buffer

69 82 0 0 0 5 0 0 0 206 180 214

I think Data in swift use Unit8 data type that reason I have difference output. My question, in swift how can I get output same java. thank you so much !

EDIT : output code

looks like java prints out its values signed, while swift is unsigned, aka -50 = 206 etc ... -128 - 128 vs 0 - 256 — Fonix, Oct 18 '16 at 05:04
FYI - since you are dealing with byte data, I'd suggest you update the Java code to print like the Swift code. — rmaddy, Oct 18 '16 at 05:13

score 1 · Answer 1 · answered Oct 18 '16 at 08:41

Data is a collection of unsigned bytes (UInt8). If you really want to print them as signed bytes then you can use Int8(bitPattern:) which creates a signed value with the same memory representation:

let buffer = Data(bytes: [69, 82, 0, 0, 0, 5, 0, 0, 0, 206, 180, 214])
for byte in buffer {
    print(Int8(bitPattern: byte))
}
// 69 82 0 0 0 5 0 0 0 -50 -76 -42

Or create an [Int8] array from the data and print the array:

let signedByteArray = buffer.map { Int8(bitPattern: $0) } // [Int8]
print(signedByteArray)
// [69, 82, 0, 0, 0, 5, 0, 0, 0, -50, -76, -42]

this is what I need, thank you so much !. I really wanna give this answer one thumbs up but I dont have enough reputation now . sorry !! — er lear, Oct 18 '16 at 08:55

score 0 · Accepted Answer · edited May 23 '17 at 11:52

0

In your java code you can try do this method which is quite straight forward to make it unsigned while printing

for(int i = 0; i<buffer.length ; i++){
     Log.e("buff","buff "+ (buffer[i] & 0xFF));
}

edited May 23 '17 at 11:52

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answered Oct 18 '16 at 05:14

Fonix

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Thank Fonix for your answer! how can I convert 206 to -56 – er lear Oct 18 '16 at 08:24
sorry I have mistake, I wanna convert 206 to -50 , 180 to -76, 214 to -42 as above question – er lear Oct 18 '16 at 08:32

difference between FileHandle in Swift 3.0 and FileInputStream in java

2 Answers2