Group
File Handling in C#
Objective
1. The program requires the user to provide the name of the BMP file to be encrypted or decrypted.
2. It reads the first two bytes of the file to identify if it starts with "BM" or "MB".
3. If the first two bytes are "BM", the program will replace them with "MB" (encryption).
4. If the first two bytes are "MB", the program will replace them with "BM" (decryption).
5. Use the program as follows:
encryptDecrypt myImage.bmp
6. The program modifies the file in place and does not create a new file.
Create a program to encrypt/decrypt a BMP image file by changing the "BM" mark in the first two bytes to "MB" and vice versa.
Use the advanced FileStream constructor to enable simultaneous reading and writing.
Example C# Exercise
Show C# Code
using System;
using System.IO;
class BMPEncryptDecrypt
{
// Main method where the program starts execution
static void Main(string[] args)
{
// Check if the user provided the correct number of arguments
if (args.Length != 1)
{
Console.WriteLine("Usage: encryptDecrypt ");
return;
}
// Get the input BMP file name from the arguments
string fileName = args[0];
// Check if the specified file exists
if (!File.Exists(fileName))
{
Console.WriteLine("The specified file does not exist.");
return;
}
try
{
// Open the file with FileStream for both reading and writing
using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.ReadWrite))
{
// Read the first two bytes of the file to check the "BM" marker
byte[] buffer = new byte[2];
fs.Read(buffer, 0, 2);
// Check if the first two bytes are "BM" or "MB"
if (buffer[0] == 'B' && buffer[1] == 'M')
{
// If it's "BM", change it to "MB" (encryption)
Console.WriteLine("Encrypting file...");
// Move the file pointer back to the start of the file
fs.Seek(0, SeekOrigin.Begin);
// Write "MB" instead of "BM"
fs.WriteByte((byte)'M'); // Write 'M'
fs.WriteByte((byte)'B'); // Write 'B'
Console.WriteLine("File encrypted successfully.");
}
else if (buffer[0] == 'M' && buffer[1] == 'B')
{
// If it's "MB", change it to "BM" (decryption)
Console.WriteLine("Decrypting file...");
// Move the file pointer back to the start of the file
fs.Seek(0, SeekOrigin.Begin);
// Write "BM" instead of "MB"
fs.WriteByte((byte)'B'); // Write 'B'
fs.WriteByte((byte)'M'); // Write 'M'
Console.WriteLine("File decrypted successfully.");
}
else
{
// If the first two bytes are not "BM" or "MB", print an error
Console.WriteLine("The file does not have the expected 'BM' or 'MB' marker.");
}
}
}
catch (Exception ex)
{
// Handle any exceptions that may occur during file processing
Console.WriteLine("An error occurred: " + ex.Message);
}
}
}
Output
//For example, if you run the program on a BMP file named myImage.bmp:
//When encrypting (changing "BM" to "MB"):
Encrypting file...
File encrypted successfully.
//When decrypting (changing "MB" back to "BM"):
Decrypting file...
File decrypted successfully.