Develop Reference

Writing Data into a File on Hololens

in my Hololens app i want to write data into a file which i can then view over the Device Portal. The Data contains just the time from one airtap on a special object to another airtap.
The problem ist that there will be no file created in the Device Portal under /LocalAppData/YourApp/LocalState
Thanks in advance
Jonathan
public void StopTime()
{
TimeSpan ts = time.Elapsed;
time.Stop();
path = Path.Combine(Application.persistentDataPath, "Messdaten.txt");
using (TextWriter writer = File.CreateText(path))
{
writer.Write(ts);
}
}

I usually use a FileStream and a StreamWriter and make sure the FileMode.Create is set.
See also How to write text to a file for more approaches
using (var file = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.Write))
{
using (var writer = new StreamWriter(file, Encoding.UTF8))
{
writer.Write(content);
}
}
With that I never had any trouble on the HoloLens so far.
You also might want to use something like ts.ToString() in order to format the value to your needs.
Alternatively you could also try Unity's Windows.File (only available for UWP) but than you need to have byte[] as input. E.g. from here
long c = ts.Ticks;
byte[] d = BitConverter.GetBytes(c);
File.WriteAllBytes(path, d);

The simplest thing to do is to use File.WriteAllText method https://learn.microsoft.com/en-us/dotnet/api/system.io.file.writealltext?view=netframework-4.7.2
Obviously there are many ways that could work but it is good to stick to the simplest solution.

Decompress Stream to String using SevenZipSharp

I'd like to compress a string using SevenZipSharp and have cobbled together a C# console application (I'm new to C#) using the following code, (bits and pieces of which came from similar questions here on SO).
The compress part seems to work (albeit I'm passing in a file instead of a string), output of the compressed string to the console looks like gibberish but I'm stuck on the decompress...
I'm trying to do the same thing as here (I think):
https://stackoverflow.com/a/4305399/3451115
https://stackoverflow.com/a/45861659/3451115
https://stackoverflow.com/a/36331690/3451115
Appreciate any help, ideally the console will display the compressed string followed by the decompressed string.
Thanks :)
using System;
using System.IO;
using SevenZip;
namespace _7ZipWrapper
{
public class Program
{
public static void Main()
{
SevenZipCompressor.SetLibraryPath(#"C:\Temp\7za64.dll");
SevenZipCompressor compressor = new SevenZipCompressor();
compressor.CompressionMethod = CompressionMethod.Ppmd;
compressor.CompressionLevel = SevenZip.CompressionLevel.Ultra;
compressor.ScanOnlyWritable = true;
var compStream = new MemoryStream();
var decompStream = new MemoryStream();
compressor.CompressFiles(compStream, #"C:\Temp\a.txt");
StreamReader readerC = new StreamReader(compStream);
Console.WriteLine(readerC.ReadToEnd());
Console.ReadKey();
// works up to here... below here output to consol is: ""
SevenZipExtractor extractor = new SevenZip.SevenZipExtractor(compStream);
extractor.ExtractFile(0, decompStream);
StreamReader readerD = new StreamReader(decompStream);
Console.WriteLine(readerD.ReadToEnd());
Console.ReadKey();
}
}
}

The result of compression is binary data - it isn't a string. If you try to read it as a string, you'll just see garbage. That's to be expected - you shouldn't be treating it as a string.
The next problem is that you're trying to read from compStream twice, without "rewinding" it first. You're starting from the end of the stream, which means there's no data for it to decompress. If you just add:
compStream.Position = 0;
before you create the extractor, you may well find it works immediately. You may also need to rewind the decompStream before reading from it. So you'd have code like this:
// Rewind to the start of the stream before decompressing
compStream.Position = 0;
SevenZipExtractor extractor = new SevenZip.SevenZipExtractor(compStream);
extractor.ExtractFile(0, decompStream);
// Rewind to the start of the decompressed stream before reading
decompStream.Position = 0;

Memory Issue in string C#

I have little test program
public class Test
{
public string Response { get; set; }
}
My console simply call Test class
class Program
{
static void Main(string[] args)
{
Test t = new Test();
using (StreamReader reader = new StreamReader("C:\\Test.txt"))
{
t.Response = reader.ReadToEnd();
}
t.Response = t.Response.Substring(0, 5);
Console.WriteLine(t.Response);
Console.Read();
}
}
I have appox 60 MB data in my Test.txt file. When the program get executes, it is taking lot of memory because string is immutable. What is the better way handle this kind of scenario using string.
I know that i can use string builder. but i have created this program to replicate a scenario in one of my production application which uses string.
when i tried with GC.Collect(), memory is released immediately. I am not sure whether i can call GC in code.
Please help. Thanks.
UPDATE:
I think i did not explain it clearly. sorry for the confusion.
I am just reading data from file to get huge data as don't want create 60MB of data in code.
My pain point is below line of code where i have huge data in Response field.
t.Response = t.Response.Substring(0, 5);

You could limit your reads to a block of bytes (buffer). Loop through and read the next block into your buffer and write that buffer out. This will prevent a large chunk of data being stored in memory.
using (StreamReader reader = new StreamReader(#"C:\Test.txt", true))
{
char[] buffer = new char[1024];
int idx = 0;
while (reader.ReadBlock(buffer, idx, buffer.Length) > 0)
{
idx += buffer.Length;
Console.Write(buffer);
}
}

Can you read your file line by line? If so, I would recommend calling:
IEnumerable<string> lines = File.ReadLines(path)
When you iterate this collection using
foreach(string line in lines)
{
// do something with line
}
the collection will be iterated using lazy evaluation. That means the entire contents of the file won't need to be kept in memory while you do something with each line.

StreamReader provides just version of Read that you looking for - Read(Char[], Int32, Int32) - which lets you pick out first characters of the stream. Alternatively you can read char-by-char with regular StreamReader.Read till you decided that you have enough.
var textBuffer = new char[5];
reader.ReadToEnd(textBuffer, 0, 5); // TODO: check if it actually read engough
t.Response = new string(textBuffer);
Note that if you know encoding of the stream you may use lower level reading as byte array and use System.Text.Encoding classes to construct strings with encoding yourself instead of relaying on StreamReader.

Convert .db to binary

I'm trying to convert a .db file to binary so I can stream it across a web server. I'm pretty new to C#. I've gotten as far as looking at code snippets online but I'm not really sure if the code below puts me on the right track. How I can write the data once I read it? Does BinaryReader automatically open up and read the entire file so I can then just write it out in binary format?
class Program
{
static void Main(string[] args)
{
using (FileStream fs = new FileStream("output.bin", FileMode.Create))
{
using (BinaryWriter bw = new BinaryWriter(fs))
{
long totalBytes = new System.IO.FileInfo("input.db").Length;
byte[] buffer = null;
BinaryReader binReader = new BinaryReader(File.Open("input.db", FileMode.Open));
}
}
}
}
Edit: Code to stream the database:
[WebGet(UriTemplate = "GetDatabase/{databaseName}")]
public Stream GetDatabase(string databaseName)
{
string fileName = "\\\\computer\\" + databaseName + ".db";
if (File.Exists(fileName))
{
FileStream stream = File.OpenRead(fileName);
if (WebOperationContext.Current != null)
{
WebOperationContext.Current.OutgoingResponse.ContentType = "binary/.bin";
}
return stream;
}
return null;
}
When I call my server, I get nothing back. When I use this same type of method for a content-type of image/.png, it works fine.

All the code you posted will actually do is copy the file input.db to the file output.bin. You could accomplish the same using File.Copy.
BinaryReader will just read in all of the bytes of the file. It is a suitable start to streaming the bytes to an output stream that expects binary data.
Once you have the bytes corresponding to your file, you can write them to the web server's response like this:
using (BinaryReader binReader = new BinaryReader(File.Open("input.db",
FileMode.Open)))
{
byte[] bytes = binReader.ReadBytes(int.MaxValue); // See note below
Response.BinaryWrite(bytes);
Response.Flush();
Response.Close();
Response.End();
}
Note: The code binReader.ReadBytes(int.MaxValue) is for demonstrating the concept only. Don't use it in production code as loading a large file can quickly lead to an OutOfMemoryException. Instead, you should read in the file in chunks, writing to the response stream in chunks.
See this answer for guidance on how to do that
https://stackoverflow.com/a/8613300/141172

Convert MP4 to Ogg with C#

Does anyone know a simple way of converting a mp4 file to an ogg file?
Have to do it, but don't have much knowlegde about it, and all I can find are programs, not examples or libraries.
Thanks in advance

I would recommend dispatching this to FFMPEG - http://www.ffmpeg.org/ - using a Process and command line arguments. You can redirect I/O if you need to (e.g. logging). Just do something like process.WaitForExit() after you've started it. You could do this on a background thread (BackgroundWorker, ThreadPool, etc...) if you need to not block the UI.

Extending Chad's answer I used the NReco.VideoConverter which is a helpful wrapper for FFMPEG. My code to convert a MP4 to OGG is as follows.
1.Save the file to a temporary file in local storage.
var path = Path.GetTempPath() + name;
using (var file = File.Create(path))
{
stream.Seek(0, SeekOrigin.Begin);
await stream.CopyToAsync(file);
file.Close();
return path;
}
2.Now use the video converter to convert the file, simple!
var output = new MemoryStream();
var ffMpeg = new FFMpegConverter();
ffMpeg.ConvertMedia(filePath, output, Format.ogg);
output.Seek(0, SeekOrigin.Begin);
return output;

static void Mp4ToOgg(string fileName)
{
DsReader dr = new DsReader(fileName);
if (dr.HasAudio)
{
string waveFile = fileName + ".wav";
WaveWriter ww = new WaveWriter(File.Create(waveFile),
AudioCompressionManager.FormatBytes(dr.ReadFormat()));
ww.WriteData(dr.ReadData());
ww.Close();
dr.Close();
try
{
Sox.Convert(#"sox.exe", waveFile, waveFile + ".ogg", SoxAudioFileType.Ogg);
}
catch (SoxException ex)
{
throw;
}
}
}
from How to converts a mp4 file to an ogg file