FileStream in .Net (C#)

FileStream class can be used to read / write data to files. FileStream class is derived from abstract Stream class. FileStream supports synchronous or asynchronous read/write operations. By default FileStream opens file synchronously. FileStream also supports random access using seek method. You can open file by passing string file name (path) to FileStream constructor. You can also specify FileMode and FileAccess along with filename. FileMode specifies how file should open while FileAccess specifies file should open for Read or Write or Both operations. 


Below is the details about FileMode and FileAccess enum.

FileModes	Description
Open	Opens an existing file for writing.
OpenOrCreate	Opens an existing file if not found creates new.
Create	Creates new file, if exists it will be overwrite.
CreateNew	Creates new file, if already exists throws an error.
Append	Opens an existing file and seek to end. If not exists creates new file.

FileAccess	Description
Read	Allows only read from file.
Write	Allows only write to file.
ReadWrite	Allows read/write to file.

Below examples shows how we can use FileModes and FileAccesss with FileStream.

//Opens an existing file for read operations

FileStream fs = new FileStream(@"d:\temp\test.txt", FileMode.Open, FileAccess.Read);

//Opens an existing file for write operations

FileStream fs = new FileStream(@"d:\temp\test.txt", FileMode.Open, FileAccess.Write);

//Opens an existing file for read/write operations

FileStream fs = new FileStream(@"d:\temp\test.txt", FileMode.Open, FileAccess.ReadWrite);

//creates new file, if exists it will be overwritten

FileStream fs = new FileStream(@"d:\temp\test.txt", FileMode.Create);

//Opens an existing file and seek to end. if not exists creates new file.

FileStream fs = new FileStream(@"d:\temp\test.txt", FileMode.Append);

Read/Write data using FileStream Read/Write methods.

//Write data

using (FileStream fs = new FileStream(@"d:\temp\test.txt", FileMode.Create, FileAccess.Write))

{

    string start = "Hello World!!!";

    byte[] byts = System.Text.Encoding.ASCII.GetBytes(start);

    fs.Write(byts, 0, byts.Length);

}

//Read data

using (FileStream fs = new FileStream(@"d:\temp\test.txt", FileMode.Open, FileAccess.Read))

{

    byte[] byts = new byte[1024];

    while (fs.Read(byts, 0, byts.Length) > 0)

    {

        Console.WriteLine(System.Text.Encoding.ASCII.GetString(byts));

    }

}

Output –

See Also - 

StreamReader / StreamWriter in .Net (C#)
BinaryReader / BinaryWriter in .Net (C#)

Performance counters in .Net (C#)