File.Open(String, FileMode) Method in C# with Examples

File.Open(String, FileMode) is an inbuilt File class method which is used to open a FileStream on the specified path with read/write access with no sharing.
Syntax:

public static System.IO.FileStream Open (string path, System.IO.FileMode mode);

Parameter: This function accepts two parameters which are illustrated below: 

• sourceFileName: This is the specified file to open.
• mode: This mode value specifies whether a new file is created if one does not exist, and also determines whether the existing file’s contents are retained or overwritten.

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 given path, file name, or both exceed the system-defined maximum length.
• DirectoryNotFoundException: The specified path is invalid.
• IOException: An I/O error occurred while opening the file.
• UnauthorizedAccessException: The path specified a file that is read-only. OR this operation is not supported on the current platform. OR the path specified a directory. OR the caller does not have the required permission.OR the mode is Created and the specified file is a hidden file.
• ArgumentOutOfRangeException: The mode specified an invalid value.
• FileNotFoundException: The file specified in the path was not found.
• NotSupportedException: The path is in an invalid format.

Return Value: Returns a FileStream opened in the specified mode and path, with read/write access and not shared.
Below are the programs to illustrate the File.Open(String, FileMode) method.
Program 1: Below code creates a temporary file, writes some specified contents into it, then open the file and print it.

CSharp

// C# program to illustrate the usage
// of File.Open(String, FileMode) method

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

class GFG {
    public static void Main()
    {
        // Creating a temporary file
        string path = Path.GetTempFileName();
        using(FileStream fs = File.Open(path, FileMode.Open))
        {
            // Putting some contents
            Byte[] info = new UTF8Encoding(true).GetBytes("GFG is a CS Portal.");
            fs.Write(info, 0, info.Length);
        }

        // Opening the stream and reading it back.
        using(FileStream fs = File.Open(path, FileMode.Open))
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b, 0, b.Length) > 0) {
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}

Output:

GFG is a CS Portal.

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

This below code will open the file file.txt and will print its contents.

CSharp

// C# program to illustrate the usage
// of File.Open(String, FileMode) 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 path
        string path = @"file.txt";

        // Opening above file and reading it back.
        using(FileStream fs = File.Open(path, FileMode.Open))
        {
            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));
            }
        }
    }
}

Output:

GeeksforGeeks