Memory stream is not expandable even when incapsulated in using()

Question

I am using multiple memory streams to convert my file names to stream and write in them like so:

public static void Save() {
    try {
        using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes("Clients.txt"))) {
            using(StreamWriter sw = new StreamWriter(ms)) {
                writeClients(sw);
            } */ Line 91 */
        }

        using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes("Hotels.txt"))) {
            using(StreamWriter sw = new StreamWriter(ms)) {
                writeHotels(sw);
            }
        } 
        [...]
    } catch {
        [...]
    }
}

but somehow when I call Save() I get the following error:

Unhandled Exception: System.NotSupportedException: Memory stream is not expandable.
   at System.IO.__Error.MemoryStreamNotExpandable()
   at System.IO.MemoryStream.set_Capacity(Int32 value)
   at System.IO.MemoryStream.EnsureCapacity(Int32 value)
   at System.IO.MemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.StreamWriter.Flush(Boolean flushStream, Boolean flushEncoder)
   at System.IO.StreamWriter.Dispose(Boolean disposing)
   at System.IO.TextWriter.Dispose()
   at csharp.Program.Save() in /home/nids/Documents/csharp/Program.cs:line 91
   at csharp.Program.Main(String[] args) in /home/nids/Documents/csharp/Program.cs:line 290

Where line 290 is the line where I call Save()

I'm not sure what's causing the error!

@QualityCatalyst Line 91 is the 6th line in the code I posted which is the bracket that closes using of the StreamWriter — Meryem, May 21 '17 at 22:46

score 3 · Accepted Answer · edited May 23 '17 at 11:47

3

You have created a memory stream that reads from the utf8 representation of the string Clients.txt, not from a file.

Memory streams that wrap a fixed byte array are non-resizable so you can't write more than the size of the byte array you initialise them with.

If your intention was to write to a file, refer to How to Write to a file using StreamWriter?

edited May 23 '17 at 11:47

Community

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answered May 21 '17 at 22:46

Martin Ullrich

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score 1 · Answer 2 · answered May 21 '17 at 22:49

If you create a MemoryStream over a pre-allocated byte array, it can't expand (ie. get longer than the size you specified when you started)

var length =Encoding.UTF8.GetBytes("Clients.txt");
  //    the length here is 11 bytes

you are pre-allocating a buffer of 11 bytes and not the length of the file so when you try to read a string upper than 11 bytes you will get an error

if you need to get the length of the file you should use FileInfo.Length

Memory stream is not expandable even when incapsulated in using()

2 Answers2

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