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File.OpenRead() Method in C# with Examples

  • Last Updated : 25 Feb, 2021

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
 

file.txt

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-
 

file.txt

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.

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