File.ReadAllBytes() Method in C# with Examples

File.ReadAllBytes(String) is an inbuilt File class method that is used to open a specified or created binary file and then reads the contents of the file into a byte array and then closes the file.
Syntax:

public static byte[] ReadAllBytes (string path);

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

• path: This is the specified file to open 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.
• IOException: An I/O error occurred while opening the file.
• UnauthorizedAccessException: This operation is not supported on the current platform. OR 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.
• SecurityException: The caller does not have the required permission.

Return Value: Returns a byte array containing the contents of the file.
Below are the programs to illustrate the File.ReadAllBytes(String) method.
Program 1: Initially, a file file.txt is created with some contents shown below-

C#

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

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

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

        // Calling the ReadAllBytes() function
        byte[] readText = File.ReadAllBytes(path);
        foreach(byte s in readText)
        {
            // Printing the binary array value of
            // the file contents
            Console.WriteLine(s);
        }
    }
}

Output:

53

Program 2: Initially, no file was created. Below code itself create a file file.txt with some specified contents.

C#

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

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

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

        // Adding below contents to the file
        string[] createText = { "GFG" };
        File.WriteAllLines(path, createText);

        // Calling the ReadAllBytes() function
        byte[] readText = File.ReadAllBytes(path);
        foreach(byte s in readText)
        {
            // Printing the binary array value of
            // the file contents
            Console.WriteLine(s);
        }
    }
}

Output:

71
70
71
10