CODEWITHSUNDEEP
c#iobinary
Steve
Steve

Reputation: 31

Why i cannot write a binary file?

I am trying to write and read binary file in a WinForm. I thought that I did it but when I try to read the file, I only get the new number that was written to the file (random numbers generated every 5 seconds), that file does not retain the previous figures. what i did:

private void timer1_Tick(object sender, EventArgs e)
        {
            string path = @"C:\Test\test.dat";
            lbl1.Text = string.Format("{0:0.0}", -6 + rand.NextDouble() * 17);
            double temp = Convert.ToDouble(lbl1.Text);
            try
            {
                  if (!File.Exists(path))
                  {
                    lock (sync)
                    {
                      FileStream outf = new FileStream(path, FileMode.CreateNew, FileAccess.Write);
                      BinaryWriter bw = new BinaryWriter(outf);
                      bw.Write(temp);
                      bw.Close();
                    }
                  }
                  else if (File.Exists(path))
                  {
                    lock (synk)
                    {
                       FileStream outf1 = new FileStream(path, FileMode.Create, FileAccess.Write);
                       BinaryWriter bw1 = new BinaryWriter(outf1);
                       bw1.Write(temp);
                       bw1.Flush();
                       bw1.Close();
                    }
                  }
                }
            catch (System.IO.FileNotFoundException ioe)
            {
              MessageBox.Show(ioe.Message);
            }

What am I doing wrong? Is there anyone who can help me? Thanks in advance.

Upvotes: 0

Views: 265

Answers (2)

Thomas Weller
Thomas Weller

Reputation: 59633

What you're doing wrong:

if (!File.Exists(path))
...
else if (File.Exists(path))
...

A simple else would have been enough.

However, not that exceptions can still happen if someone would create the file after the "not exists" check has already been performed or the file gets deletes after the "exists" check has been performed.

lock (sync)
...
lock (synk)

You are locking on different synchronization objects.

Other than that, the code will always be executed on the same thread (UI thread), since timer ticks are handled by Windows messages. This means, the lock statment can probably be omitted (if you don't have use threads explicitly somewhere else).

but when I try to read the file

Actually both code pieces are writing to the file.

bw.Write(temp);
...
bw1.Write(temp);

FileMode.Create (MSDN) overwrites existing files. FileMode.Open and FileAccess.Read would be better suited for reading.

Then, of course, use a BinaryReader (MSDN).

Upvotes: 2

D Stanley
D Stanley

Reputation: 152624

You are opening the stream using FileMode.Create, which overwrites the existing file. Use FileMode.Append instead.

Note that you don't have to check to see if the file exists or not; you can use FileMode.OpenOrCreate | FileMode.Append to create it if it doesn't exist:

try
{
    lock (sync)
    {
       FileStream outf = new FileStream(path, FileMode.OpenOrCreate | FileMode.Append, FileAccess.Write);
       BinaryWriter bw = new BinaryWriter(outf);
       bw.Write(temp);
       bw.Flush();
       bw.Close();
    }
}

Upvotes: 4

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