C＃尝试在使用MemoryStream类时替换一个字节

Question

I get a text file from a mainframe and sometimes there are some 0x0D injected into the middle of the text lines.

The previos programmer created a method using the FileStream class. This method works fine but is taking around 30 minutes to go thru the entire file.

My thought was to pass the text lines that are needed (about 25 lines) to a method to decrease the processing time.

I've been working with the MemoryStream class but am having issue where it does not find the 0x0D control code.

Here is the current FileStream method:

private void ReplaceFileStream(string strInputFile)
{
    FileStream fileStream = new FileStream(strInputFile, FileMode.Open, FileAccess.ReadWrite);
    byte filebyte;

    while (fileStream.Position < fileStream.Length)
    {
        filebyte = (byte)fileStream.ReadByte();
        if (filebyte == 0x0D)
        {
            filebyte = 0x20;
            fileStream.Position = fileStream.Position - 1;
            fileStream.WriteByte(filebyte);
        }
    }
    fileStream.Close();
}

and here is the MemoryStream method:

private void ReplaceMemoryStream(string strInputLine)
{
    byte[] byteArray = Encoding.ASCII.GetBytes(strInputLine);
    MemoryStream fileStream = new MemoryStream(byteArray);

    byte filebyte;

    while (fileStream.Position < fileStream.Length)
    {
        filebyte = (byte)fileStream.ReadByte();
        if (filebyte == 0x0D)
        {
            filebyte = 0x20;
            fileStream.Position = fileStream.Position - 1;
            fileStream.WriteByte(filebyte);
        }
    }
    fileStream.Close();
}

As I have not used the MemoryStream class before am not that familar with it. Any tips or ideas?

Answer 1

I don't know the size of your files, but if they are small enough that you can load the whole thing in memory at once, then you could do something like this:

private void ReplaceFileStream(string strInputFile)
{
    byte[] fileBytes = File.ReadAllBytes(strInputFile);
    bool modified = false;
    for(int i=0; i < fileBytes.Length; ++i)
    {
        if (fileByte[i] == 0x0D)
        {
            fileBytes[i] = 0x20;
            modified = true;
        }
    } 

    if (modified)
    {
        File.WriteAllBytes(strInputFile, fileBytes);
    }
}

If you can't read the whole file in at once, then you should switch to a buffered reading type of setup, here is an example that reads from the file, writes to a temp file, then in the end copies the temp file over the original file. This should yield better performance then reading a file one byte at a time:

private void ReplaceFileStream(string strInputFile)
{
    string tempFile = Path.GetTempFileName();
    try
    {
        using(FileStream input = new FileStream(strInputFile,
            FileMode.Open, FileAccess.Read))
        using(FileStream output = new FileStream(tempFile,
            FileMode.Create, FileAccess.Write))
       {
           byte[] buffer = new byte[4096];
           bytesRead = input.Read(buffer, 0, 4096);
           while(bytesRead > 0)
           {
                for(int i=0; i < bytesRead; ++i)
                {
                    if (buffer[i] == 0x0D)
                    {
                        buffer[i] = 0x20;
                    }
                }

                output.Write(buffer, 0, bytesRead);
                bytesRead = input.Read(buffer, 0, 4096);
            }
            output.Flush();
        }

        File.Copy(tempFile, strInputFile);
    }
    finally
    {
        if (File.Exists(tempFile))
        {
            File.Delete(tempFile);
        }
    }
}

Answer 2

if your replacement code does not find the 0x0D in the stream and the previous method with the FileStream does it, I think it could be because of the Encoding you are using to get the bytes of the file, you can try with some other encoding types.

otherwise your code seems to be fine, I would use a using around the MemoryStream to be sure it gets closed and disposed, something like this:

using(var fileStream = new MemoryStream(byteArray))
{

  byte filebyte;

 // your while loop...

}

looking at your code I am not 100% sure the changes you make to the memory stream will be persisted; Actually I think that if you do not save it after the changes, your changes will be lost. I can be wrong in this but you should test and see, if it does not save you should use StreamWriter to save it after the changes.