CODEWITHSUNDEEP
c#.netvb.netiobinary
Eggord
Eggord

Reputation: 13

Simultaneously read and write binary file

I want to write and read a binary file simultaneously, but whenever I try to do so I always get an exception stating that the file is already in use by a different process. I know how to do it with a normal FileStream but with a BinaryReader and BinaryWriter it doesn't work.

Does anybody have an idea how to read and write a binary file simultaneously?

What I've done so far:

FileSt = New FileStream("file.bin", FileMode.Create,FileAccess.ReadWrite)
writer = New BinaryWriter(FileSt, enc)
reader = New BinaryReader(File.Open("file.bin", FileMode.Open))

Upvotes: 0

Views: 1856

Answers (3)

jmcilhinney
jmcilhinney

Reputation: 54417

You're opening the file twice - once for reading and once for writing. That means that one FileStream needs FileAccess.Read and FileShare.Write while the other needs FileAccess.Write and FileShare.Read. This code is tested and verified with a file that had already had an Integer and a String written to it with a BinaryWriter:

Dim filePath As String = Path.Combine(My.Computer.FileSystem.SpecialDirectories.MyDocuments, "Test.bin")

Using source = File.Open(filePath, FileMode.Open, FileAccess.Read, FileShare.Write),
      destination = File.Open(filePath, FileMode.Open, FileAccess.Write, FileShare.Read),
      reader As New BinaryReader(source),
      writer As New BinaryWriter(destination)
    Dim n = reader.ReadInt32()

    writer.Write(98765)
    writer.Write("What's up doc?")

    Dim sz = reader.ReadString()
End Using

Note that you should only specify Read or Write if that's all that's needed. Only specify ReadWrite if you know that you will or might need both. The FileAccess value is for what this FileStream will do or may do to the file while the FileShare value is for what other FileStream objects opened on the same file are allowed to do.

Upvotes: 0

BertZ
BertZ

Reputation: 13

You need to set the FileShare mode on the file.

        FileStream blah = new FileStream("file.bin", FileMode.Create, FileAccess.ReadWrite, FileShare.ReadWrite);

Upvotes: 0

Matías Fidemraizer
Matías Fidemraizer

Reputation: 64933

You need to use the FileStream constructor overload that can provide FileShare mode.

See what MSDN states about FileShare.ReadWrite mode:

Allows subsequent opening of the file for reading or writing. If this flag is not specified, any request to open the file for reading or writing (by this process or another process) will fail until the file is closed. However, even if this flag is specified, additional permissions might still be needed to access the file.

Upvotes: 2

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