File.OpenRead() Method in C# with Examples

File.OpenRead(String) is an inbuilt File class method which is used to open an existing file for reading.
Syntax:

public static System.IO.FileStream OpenRead (string path);

Parameter: This function accepts a parameter which is illustrated below: 

• path: This is the specified file which is going to be opened for reading.

Exceptions:

• ArgumentException: The path is a zero-length string, contains only white space, or one or more invalid characters as defined by InvalidPathChars.
• ArgumentNullException: The path is null.
• PathTooLongException: The specified path, file name, or both exceed the system-defined maximum length.
• DirectoryNotFoundException: The specified path is invalid.
• UnauthorizedAccessException: The path specified a directory. OR the caller does not have the required permission.
• FileNotFoundException: The file specified in the path was not found.
• NotSupportedException: The path is in an invalid format.
• IOException: An I/O error occurred while opening the file.

Return Value: Returns a read-only FileStream on the specified path.
Below are the programs to illustrate the File.OpenRead(String) method.
Program 1: Before running the below code, a file file.txt is created with some contents shown below

Below code open the file file.txt for reading.

C#

// C# program to illustrate the usage
// of File.OpenRead(String) method

// Using System, System.IO and
// System.Text namespaces
using System;
using System.IO;
using System.Text;

class Test {
    public static void Main()
    {
        // Specifying a file
        string path = @"file.txt";

        // Opening the existing file for reading
        using(FileStream fs = File.OpenRead(path))
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b, 0, b.Length) > 0) {
                // Printing the file contents
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}

Executing:

GeeksforGeeks

Program 2: Initially, a file file.txt is created with some contents shown below-

This below code will overwrite the file contents with other specified contents then final contents will be printed.

C#

// C# program to illustrate the usage
// of File.OpenRead(String) method

// Using System, System.IO and
// System.Text namespaces
using System;
using System.IO;
using System.Text;

class GFG {
    public static void Main()
    {
        // Specifying a file
        string path = @"file.txt";

        // Opening the file for overwriting with
        // another contents
        using(FileStream fs = File.OpenWrite(path))
        {
            Byte[] info = new UTF8Encoding(true).GetBytes("GFG is a CS portal.");
            fs.Write(info, 0, info.Length);
        }

        // Opening the existing file for reading
        using(FileStream fs = File.OpenRead(path))
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b, 0, b.Length) > 0) {
                // Printing the file contents
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}

Executing:

GFG is a CS portal.