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File Input and Output in C

A file is a collection of data stored on a disk with a specified name and directory path. When a file is opened for reading or writing, it becomes a stream.

Fundamentally, a stream is a sequence of bytes transmitted over a communication path. There are two main types of streams: input streams and output streams. Input streams are used to read data from a file (read operations), and output streams are used to write data to a file (write operations).

C# I/O Classes

The System.IO namespace contains various classes for performing numerous file operations, such as creating and deleting files, reading from or writing to files, and closing files.

The following table lists some commonly used non-abstract classes in the System.IO namespace:

I/O Class	Description
BinaryReader	Reads primitive data from a binary stream.
BinaryWriter	Writes primitive data in binary format.
BufferedStream	Temporary storage for a stream of bytes.
Directory	Helps manipulate directory structures.
DirectoryInfo	Used for performing operations on directories.
DriveInfo	Provides information about drives.
File	Helps manipulate files.
FileInfo	Used for performing operations on files.
FileStream	Used for reading and writing at any location in a file.
MemoryStream	Used for random access to streamed data stored in memory.
Path	Performs operations on path information.
StreamReader	Used for reading characters from a byte stream.
StreamWriter	Used for writing characters to a stream.
StringReader	Used for reading from a string buffer.
StringWriter	Used for writing to a string buffer.

FileStream Class

The FileStream class in the System.IO namespace helps with reading, writing, and closing files. This class derives from the abstract class Stream.

You need to create a FileStream object to create a new file or open an existing one. The syntax for creating a FileStream object is as follows:

FileStream <object_name> = new FileStream(<file_name>, &lt;FileMode Enumerator>, &lt;FileAccess Enumerator>, &lt;FileShare Enumerator>);

For example, to create a FileStream object F to read a file named sample.txt:

FileStream F = new FileStream("sample.txt", FileMode.Open, FileAccess.Read, FileShare.Read);

Parameter	Description
FileMode	The FileMode enumeration defines various methods for opening files. Members of the FileMode enumeration include: Append: Opens an existing file and places the cursor at the end of the file. If the file does not exist, it creates one. Create: Creates a new file. If the file already exists, it deletes the old file and creates a new one. CreateNew: Specifies that the operating system should create a new file. If the file already exists, an exception is thrown. Open: Opens an existing file. If the file does not exist, an exception is thrown. OpenOrCreate: Specifies that the operating system should open an existing file. If the file does not exist, it creates a new file with the specified name. Truncate: Opens an existing file, and once opened, the file is truncated to zero bytes. We can then write new data to the file, but the initial creation date of the file is retained. If the file does not exist, an exception is thrown.
FileAccess	Members of the FileAccess enumeration include: Read, ReadWrite, and Write.

Parameter

Description

FileMode

The FileMode enumeration defines various methods for opening files. Members of the FileMode enumeration include: Append: Opens an existing file and places the cursor at the end of the file. If the file does not exist, it creates one. Create: Creates a new file. If the file already exists, it deletes the old file and creates a new one. CreateNew: Specifies that the operating system should create a new file. If the file already exists, an exception is thrown. Open: Opens an existing file. If the file does not exist, an exception is thrown. OpenOrCreate: Specifies that the operating system should open an existing file. If the file does not exist, it creates a new file with the specified name. Truncate: Opens an existing file, and once opened, the file is truncated to zero bytes. We can then write new data to the file, but the initial creation date of the file is retained. If the file does not exist, an exception is thrown.

FileAccess

Members of the FileAccess enumeration include: Read, ReadWrite, and Write.

FileShare Enumeration Members:

Inheritable: Allows the file handle to be inherited by child processes. This feature is not directly supported by Win32.
None: Refuses to share the current file. Any request to open the file (made by this process or another process) will fail until the file is closed.
Read: Allows subsequent opening of the file for reading. If this flag is not specified, any request to open the file for reading (made by this process or another process) will fail until the file is closed. However, even with this flag specified, additional permissions may be required to access the file.
ReadWrite: 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 (made by this process or another process) will fail until the file is closed. However, even with this flag specified, additional permissions may be required to access the file.
Write: Allows subsequent opening of the file for writing. If this flag is not specified, any request to open the file for writing (made by this process or another process) will fail until the file is closed. However, even with this flag specified, additional permissions may be required to access the file.
Delete: Allows subsequent deletion of the file.

Example

The following program demonstrates the usage of the FileStream class:

using System;
using System.IO;

namespace FileIOApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            FileStream F = new FileStream("test.dat", 
            FileMode.OpenOrCreate, FileAccess.ReadWrite);

            for (int i = 1; i <= 20; i++)
            {
                F.WriteByte((byte)i);
            }

            F.Position = 0;

            for (int i = 0; i <= 20; i++)
            {
                Console.Write(F.ReadByte() + " ");
            }
            F.Close();
            Console.ReadKey();
        }
    }
}

When the above code is compiled and executed, it produces the following result:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 -1

Advanced File Operations in C

The above example demonstrates simple file operations in C#. However, to fully utilize the power of C# System.IO classes, you need to know the commonly used properties and methods of these classes.

In the following sections, we will discuss these classes and the operations they perform. Click on the links to learn more about each topic:

Topic	Description
Reading and Writing Text Files	It involves reading and writing text files. The StreamReader and StreamWriter classes help in reading and writing text files.
Reading and Writing Binary Files	It involves reading and writing binary files. The BinaryReader and BinaryWriter classes help in reading and writing binary files.
Operating on the Windows File System	It allows C# programmers to browse and locate Windows files and directories.

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