CODEWITHSUNDEEP
c#streamreaderstreamwritermemory-mapped-filesinter-process-communicat
Andreas Reiff
Andreas Reiff

Reputation: 8404

MemoryMappedFiles and StreamRead/StreamWriter first character missing

I want to pass some information between 2 processes. Basically, it is a number of strings, and since I dont want to restrict the strings in any way (I could pass it through command line since I spawn the 2nd process) I thought to give shared memory a go. (Named pipes seem a bit more complicated from samples.)

So I simply copy/pasted the sample (actually, sample used binary streams, I use text streams) code and use breakpoints right now for synchronization.

Sender code

        using (System.IO.MemoryMappedFiles.MemoryMappedFile mmf = System.IO.MemoryMappedFiles.MemoryMappedFile.CreateNew("mymappedfile", 10000))
        {
            using (System.IO.MemoryMappedFiles.MemoryMappedViewStream stream = mmf.CreateViewStream())
            {
                StreamWriter w = new StreamWriter(stream);
                w.WriteLine("Hello!");
                w.WriteLine("Andreas!");
                w.WriteLine("Teststring #+#\"\" ,,a8&&");
                //BinaryWriter writer = new BinaryWriter(stream);
                w.Flush();
            }
        }

Receiver code

            using (MemoryMappedFile mmf = MemoryMappedFile.OpenExisting("mymappedfile"))
            {
                using (MemoryMappedViewStream stream = mmf.CreateViewStream(1, 0))
                {
                    StreamReader r = new StreamReader(stream);
                    string str;
                    while ((str = r.ReadLine()) != null)
                    {
                        System.Diagnostics.Debug.WriteLine(str);
                    }
                }
            }

Output

ello!
Andreas!
Teststring #+#"" ,,a8&&

There is the H of Hello! missing.

Should I use BinaryStreams instead or what could be the issue here?

Upvotes: 1

Views: 1451

Answers (1)

huseyin tugrul buyukisik
huseyin tugrul buyukisik

Reputation: 11926

 mmf.CreateViewStream(1/* selects first byte */, 0)

to

 mmf.CreateViewStream(0/* selects zeroth byte*/, 0)

Here it is: http://msdn.microsoft.com/en-us/library/dd267553(v=vs.110).aspx

Like this:

public MemoryMappedViewStream CreateViewStream(
    long offset, // you have set it to 1 but should start from 0 
    long size
)

Upvotes: 2

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