Swift - writing a byte stream to file [closed]

Question

I have a string of several hundred bytes and some Int32 values. I want to write these to a file, verbatim.

I have tried many suggested solutions and none have worked for me. I get extraneous brackets or spaces or commas in the file.

Can anyone suggest a simple, reliable solution?

I thought my question was very clear, but after reading the comments, I have simplified it.

How do I write and/or append "12345" to a file so that the file contains the following Hex values: 3132333435 ?

The best result I can obtain is <3132333435>, by writing an NSData string.

I can get the desired result using this link: Does swift have a protocol for writing a stream of bytes?, but I cannot append data to the file I have created.

Disaffirm

I am interested to know why someone has downvoted my question. It is a valid and relevant question and there is no satisfactory answer that I can find – Disaffirm

The closest solution I have found is: #24184929, but I want to be able to append to a file, as well as write to it. – Disaffirm

"It is a valid and relevant question" Not if no one can understand what the question is. Try being a little more generous with your examples of input and desired output, perhaps. – Combustor

matt, my question was VERY clear and precise, but I'll simplify it. How do I write and/or append "12345" to a file so that the file contains the following Hex values: 3132333435 ? The best result I can obtain is <3132333435>, by writing an NSData string. I can get the desired result using the link I referenced above, but I cannot append data to the file. – Disaffirm

Well, I don't see what the difficulty is supposed to be. NSFileHandle is made for appending. Also I think you were doing it correctly with NSData writing to a file; you just couldn't read your own results (I've commented on that in my answer). – Combustor

Answer 1

I would suggest using NSFileHandle.

I tested like this. I started with a file ~/Desktop/test.txt containing the word "testing". I then ran this code:

    let s = "12345"
    let d = s.dataUsingEncoding(NSASCIIStringEncoding)!
    let path = ("~/Desktop/test.txt" as NSString).stringByExpandingTildeInPath
    if let fh = NSFileHandle(forWritingAtPath: path) {
        fh.seekToEndOfFile()
        fh.writeData(d)
        fh.closeFile()
    }

The result was that the file now contained

testing12345

A hex dump revealed that the underlying bytes were:

74 65 73 74 69 6E 67 31 32 33 34 35

I believe that's what you said you wanted to achieve.

Also, one further commment:

The best result I can obtain is <3132333435>

It sounds here as if the problem is merely that you don't know how to read the console output. The < and > are not really in the file; they are just part of the console representation of data. It would be better to use BBEdit / TextWrangler or a dedicated hex dumper to see the actual byte of the file.

Combustor

Thanks for adding the code. I like the simplicity of the file handle approach. I know how to use a hex editor. After one of my attempts, I DID see <3132333435> in the file. I can't remember how I managed that! – Disaffirm

"I DID see <3132333435> in the file" You probably passed the NSData through a String representation (which is merely a logging representation) and then wrote that into the file. – Combustor

matt, thanks for the hint. I missed the grey check mark! – Disaffirm

Answer 2

Basically the issue is going to be getting your data correctly converted to a pointer to get it to NSOutputStream.write. The following extension should do what you need:

extension NSOutputStream {
    enum WriteErrors : ErrorType {
        case UTF8ConversionFailed
    }

    func write(string:String) throws -> Int {
        guard let data = string.dataUsingEncoding(NSUTF8StringEncoding) else {
            throw WriteErrors.UTF8ConversionFailed
        }

        return write(UnsafePointer(data.bytes), maxLength: data.length)
    }

    func write(var i:Int32) throws -> Int {
        return withUnsafePointer(&i) {
            self.write(UnsafePointer($0), maxLength: sizeof(Int32))
        }
    }
}

Note that writing raw binary data to a file is ill-advised, you should be standardizing the byte order first, but I leave that as an exercise for the reader.

Girvin

David, thanks for your constructive reply. I'll experiment with your code. Regarding your comment about "raw binary data", I'm well aware of the issues. :-) I am writing to a 1975 oil-industry file format that was originally developed for 1/2" 9-track tapes! The format is well-defined, using two and four-byte two's complement integers, four-byte big-endian IEEE floating-point numbers and ASCII text. The format also supports IBM floating-point numbers and EBCDIC text, for backwards compatability! – Disaffirm