Reading from memory stream to string

Question

I am trying to write an object to an Xml string and take that string and save it to a DB. But first I need to get the string...

    private static readonly Encoding LocalEncoding = Encoding.UTF8;

    public static string SaveToString<T> (T settings)
    {
        Stream stream = null;
        TextWriter writer = null;
        string settingsString = null;

        try
        {
            stream = new MemoryStream();

            var serializer = new XmlSerializer(typeof(T));

            writer = new StreamWriter(stream, LocalEncoding);

            serializer.Serialize(writer, settings);

            var buffer = new byte[stream.Length];

            stream.Read(buffer, 0, (int)stream.Length);
            
            settingsString = LocalEncoding.GetString(buffer);
        }
        catch (Exception ex)
        {
            // If the action cancels we don't want to throw, just return null.
        }
        finally
        {
            if (stream != null)
                stream.Close();

            if (writer != null)
                writer.Close();
        }

        return settingsString;
    }

This seems to work, the stream gets filled with bytes. But when I come to read it back into the buffer and then into the string... the buffer is filled with '0'! Not sure what I doing wrong here guys.

possible duplicate of How do you get a string from a MemoryStream? — andyp
– andyp, Commented May 7, 2014 at 20:52

Community · Accepted Answer · 2017-05-23 11:47:32Z

94

If you'd checked the results of stream.Read, you'd have seen that it hadn't read anything - because you haven't rewound the stream. (You could do this with stream.Position = 0;.) However, it's easier to just call ToArray:

settingsString = LocalEncoding.GetString(stream.ToArray());

(You'll need to change the type of stream from Stream to MemoryStream, but that's okay as it's in the same method where you create it.)

Alternatively - and even more simply - just use StringWriter instead of StreamWriter. You'll need to create a subclass if you want to use UTF-8 instead of UTF-16, but that's pretty easy. See this answer for an example.

I'm concerned by the way you're just catching Exception and assuming that it means something harmless, by the way - without even logging anything. Note that using statements are generally cleaner than writing explicit finally blocks.

edited May 23, 2017 at 11:47

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answered May 4, 2012 at 9:30

Jon Skeet

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6 Comments

tigerswithguitars Over a year ago

Thanks :) . That's quick work. I know the using blocks are more usual. But I quite like the flatness this gives me, no nested usings. Which is only a style thing. I didn't know there was a StringWriter, seems much easier, but I like the ability to specify the encoing. I'll probably add an overload for this, rather than a new class.

Jon Skeet Over a year ago

@tigerswithguitars: How exactly are you intending to add an overload to StringWriter itself? The point of the new class is that StringWriter always returns UTF-16 from its TextWriter.Encoding property; the extra class just overrides that property.

tigerswithguitars Over a year ago

sorry, my wording was confusing. I will add an overload to my own method to specify the encoding.

Jon Skeet Over a year ago

@tigerswithguitars: Right, that's fine. You'll still need to add the extra StringWriter class, but that's just to use within the method.

tigerswithguitars Over a year ago

I have just finished your book... and someone up voted this today. I had forgotten You had answered this. Amazing coincidence. Also, "C# in Depth" is the BEST language book I have ever read, amazing stuff.

|

Prasanth · Accepted Answer · 2016-01-21 11:12:46Z

46

string result = System.Text.Encoding.UTF8.GetString(fs.ToArray());

edited Jan 21, 2016 at 11:12

Prasanth

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answered Jan 29, 2015 at 15:20

Farzad J

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3 Comments

oɔɯǝɹ Over a year ago

While this code sample may possibly answer the question, it would be preferable to include some the essential explanation to the answer here.

Nicolas Raoul Over a year ago

What is stem here? If a variable, how did you you instantiate it? Same question for fs.

Prasanth Over a year ago

The user has mistakenly used stem instead of System

evorios · Accepted Answer · 2015-10-19 22:40:08Z

16

string result = Encoding.UTF8.GetString((stream as MemoryStream).ToArray());

answered Oct 19, 2015 at 22:40

evorios

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2 Comments

Simon MᶜKenzie Over a year ago

I would question the use of as here - it's not protecting you from anything. Firstly, you know the stream is a MemoryStream anyway, plus, even if it wasn't, passing null into GetString will throw an exception, so you may as well use an explicit cast in the first place.

ryanyuyu Over a year ago

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value.

George Kargakis · Accepted Answer · 2018-09-13 08:20:42Z

In case of a very large stream length there is the hazard of memory leak due to Large Object Heap. i.e. The byte buffer created by stream.ToArray creates a copy of memory stream in Heap memory leading to duplication of reserved memory. I would suggest to use a StreamReader, a TextWriter and read the stream in chunks of char buffers.

In netstandard2.0 System.IO.StreamReader has a method ReadBlock

you can use this method in order to read the instance of a Stream (a MemoryStream instance as well since Stream is the super of MemoryStream):

private static string ReadStreamInChunks(Stream stream, int chunkLength)
{
    stream.Seek(0, SeekOrigin.Begin);
    string result;
    using(var textWriter = new StringWriter())
    using (var reader = new StreamReader(stream))
    {
        var readChunk = new char[chunkLength];
        int readChunkLength;
        //do while: is useful for the last iteration in case readChunkLength < chunkLength
        do
        {
            readChunkLength = reader.ReadBlock(readChunk, 0, chunkLength);
            textWriter.Write(readChunk,0,readChunkLength);
        } while (readChunkLength > 0);

        result = textWriter.ToString();
    }

    return result;
}

NB. The hazard of memory leak is not fully eradicated, due to the usage of MemoryStream, that can lead to memory leak for large memory stream instance (memoryStreamInstance.Size >85000 bytes). You can use Recyclable Memory stream, in order to avoid LOH. This is the relevant library

Yes - use StreamReader - but not because of memory leaks, but because it's just the best way to do it!

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