C#. The FileStream class. Enumeration FileOptions

The FileStream class. Additional read/write options. Enumeration FileOptions. Examples

This topic is a continuation of the topic:

Hierarchy of streams with basic storages. The FileStream class

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1. Enumeration FileOptions. The purpose

The FileStream class has a number of constructors that you can use to set different modes of file access. According to the documentation, one of the constructors of the FileStream class looks like this:

public FileStream(string path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, int bufferSize, System.IO.FileOptions options)

here

path – file path or file name;
mode – a constant from the FileMode enumeration that specifies the file open mode. You can read more about the FileMode enumeration here;
access – a constant from the FileAccess enumeration that specifies how the file is accessed. You can read more about the FileAccess enumeration here;
share – a value from the FileShare enumeration that determines whether the file can be used as a shared resource by various processes;
bufferSize – the size of the buffer used for portionwise writing/reading of data in the file. By default, bufferSize = 4096;
options – a constant from the FileOptions enumeration that specifies the various options for using the file.

The FileOptions enumeration implements additional features (options) that determine the purpose of an open file:

Asynchronous – indicates that the file can be used for asynchronous reading and writing;
DeleteOnClose – indicates that the file will be deleted after it is no longer used;
Encrypted – indicates that the file is encrypted and can only be decrypted using the same user account used for encryption;
None – indicates that no additional options apply to the generated FileStream object;
RandomAccess – indicates that the file is being accessed randomly. This hint gives the system a hint to optimize file caching;
SequentialScan – indicates that the file is being read sequentially from start to finish. This hint can be used as a hint to the system to optimize file caching. This may provide some performance improvement;
WriteThrough – instructing the system to write through any intermediate cache and go directly to disk.

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2. Examples of processing (writing / reading) a file with specified additional options FileOptions

2.1. Creating a file using options from the FileOptions enumeration

The code snippet creates a file for asynchronous reading and writing. The buffer size is set to 8192 bytes. The file can be used for asynchronous reading and writing.

...

// Create a file for asynchronous reading and writing
using (FileStream fs = new FileStream("file.bin", FileMode.Create,
FileAccess.ReadWrite, FileShare.None, 4096, FileOptions.Asynchronous))
{
  // Using fs to process a file
  ...
}

...

If in the above code, in the constructor the value

FileOptions.Asynchronous

replace with code

FileOptions.Asynchronous | FileOptions.DeleteOnClose

then after creation and use, the file named file.bin will be deleted.

In the same way, you can specify other additional file control options from the FileOptions enumeration.

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2.2. Opening a file for writing

To open a file for writing with random access, the following code can be used:

...

// Opening a file for writing
using (FileStream fs = new FileStream("file1.bin", FileMode.OpenOrCreate,
FileAccess.Write, FileShare.Write, 2048, FileOptions.RandomAccess))
{
  ...
}

...

The above snippet creates a file named file1.bin. The open mode is set equal to OpenOrCreate (open a previously created file or create a new file). The access mode is set equal to FileAccess.Write. The FileShare.Write constant indicates that the file can be a shared resource for writing from various processes (threads). The buffer size is 2048 bytes. The FileOptions constant indicates that the file is being accessed randomly.

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2.3. Opening a file for reading. An example of a byte-by-byte asynchronous file reading

To open a file for reading using constants from the FileOptions enumeration, you can use, for example, the following code

...

// Opening a file for reading
using (FileStream fs = new FileStream("file3.bin", FileMode.Open,
FileAccess.Read, FileShare.Read, 2048, FileOptions.Asynchronous))
{
  // Read bytes from file until end of file is reached
  // and write this data to array A

  // Allocate memory for buffer
  byte[] A = new byte[fs.Length];

  // additional variables
  int t, i;

  // The loop of byte data reading
  i = 0;
  do
  {
    t = fs.ReadByte(); // read the byte
    if (t != -1)
        A[i++] = (byte)t;
  }
  while (t != -1);
}

...

The previous example reads file3.bin byte by byte. The file is open for asynchronous reading. The read data is copied to byte array A.

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