Question

Description: Merge two or more text files provided by the user into a new text file where the names of the text files to join and the output text file are provided to the program using command line arguments.

Purpose: This application provides experience working with command line arguments, writing files to disk, reading files from disk, working with exceptions, and writing programs in C#/.NET.

Requirements:

Project Name: DocumentMerger2
Target Platform: Console
Programming Language: C#

In a previous challenge, Document Merger (Links to an external site.), you wrote a program to merge text documents provided by the user into a new text file where you prompted the user in the consolefor the names of the text files to merge as well as the resulting merged text file.

In this challenge, the functionality of being able to merge text documents is to be the same as Document Merger. The difference in this challenge is that the names of the text files to join and the output text file are provided to the program using command line arguments. Instead of prompting the user for the names (paths to the files), that information is provided via command line arguments.

The command line arguments are provided to the Main() function in C#:

class Program {
     static void Main(string[] args) {
          // args is a string[] of command line arguments
     
     }
}

The length of the array can be determined using the Length property of the array.

args.Length

If two text files are to be merged, three command line arguments are supplied to the program. The first two command line arguments are the the names of the text files to merge and the third command line argument is the name of the resulting merged text file. In this case the args array of strings is to contain three strings.

If three text files are to be merged, four command line arguments are supplied to the program. The first three command line arguments are the the names of the text files to merge and the fourth command line argument is the name of the resulting merged text file. In this case the args array of strings is to contain four strings.

Support for merging two or more files is to be supported in the application. The number of command line arguments minus one is the number of text files to merge. If six text files are to be merged, seven command line arguments are supplied with the seventh being the name of the resulting merged text file.

If two command line arguments or less are supplied, then a merger of text documents is not possible. In this case the user is to be presented with information on how to use the program and the program is to exit (quit).

if (args.Length < 3) {
     Console.WriteLine("DocumentMerger2 <input_file_1> <input_file_2> ... <input_file_n> <output_file>")
     Console.WriteLine("Supply a list of text files to merge followed by the name of the resulting merged text file as command line arguments.")
}

How command line arguments are supplied to a C#/.NET/Console application depends on the platform and how the program is run. Be sure to check out the following documents that cover how to write and run a program that accepts command line arguments and how to provide command line arguments to an application in different contexts (in Visual Studio/on the command line/mac OS/Windows).

• Building and Running Console App (Links to an external site.)

• Command Line Parameters Inside Visual Studio (Links to an external site.)

If any exceptions occur during the execution of the program, they are to be handled and the user is to be presented with informative error messages. The program is not to crash when an exception occurs. An exception might occur if a provided filename doesn’t exist or there is an error writing the output file.

Answer 1

• Create a file named "MergeFiles.cs" and insert the following code into it:

using System;
using System.IO;
namespace Merging
{   
class MergeFiles{   
  
// Main Method which accepts the command line arguments as string type parameters   
static void Main(string[] args)
{   
  
// If length of Command line arguments < 3 then merger of text documents is not possible
if(args.Length < 3)
{
Console.WriteLine("DocumentMerger2 <input_file_1> <input_file_2> ... <input_file_n> <output_file>");
Console.WriteLine("Supply a list of text files to merge followed by the name of the resulting merged text file as command line arguments.");
System.Environment.Exit(1); // stop the execution of program
}
else
{
StreamWriter sw = null;
try
{
// This will create a new file (merged file) with the specified name at the specified location for writing operations
sw = new StreamWriter(args[args.Length - 1] + ".txt");
}
catch (FileNotFoundException) {
Console.WriteLine("The " + args[args.Length - 1] + ".txt file cannot be found.");
}
catch (DirectoryNotFoundException) {
Console.WriteLine("The directory cannot be found.");
}
catch (DriveNotFoundException) {
Console.WriteLine("The drive specified in merged file's path is invalid.");
}
catch (PathTooLongException) {
Console.WriteLine("The merged file's path exceeds the maxium supported path length.");
}
catch (UnauthorizedAccessException) {
Console.WriteLine("You do not have permission to create " + args[args.Length - 1] + ".txt file.");
}
catch (IOException) {
Console.WriteLine("An IO exception occurred while creating " + args[args.Length - 1] + ".txt file.");
}
  
// One by one, open the text files that are to be merged, read their contents line by line and simultaneously write them into the merged file opened earlier
for(int i=0; i<args.Length-1; ++i)
{
       StreamReader sr = null;
       try
       {
       //Opening a specified text file for reading operations
       sr = new StreamReader(args[i] + ".txt");
      
       // This is use to specify to start reading the opened text file from the beginning
       sr.BaseStream.Seek(0, SeekOrigin.Begin);
       }
       catch (FileNotFoundException) {
Console.WriteLine("The " + args[i] + ".txt file cannot be found.");
}
catch (DirectoryNotFoundException) {
Console.WriteLine("The directory cannot be found.");
}
catch (DriveNotFoundException) {
Console.WriteLine("The drive specified in merged file's path is invalid.");
}
catch (PathTooLongException) {
Console.WriteLine("The merged file's path exceeds the maxium supported path length.");
}
catch (UnauthorizedAccessException) {
Console.WriteLine("You do not have permission to read " + args[i] + ".txt file.");
}
catch (IOException) {
Console.WriteLine("An IO exception occurred while opening " + args[i] + ".txt file.");
}
  

// To read a line from the file
string str = sr.ReadLine();
  
// To read the whole file line by line and simultaneously write it to the merged file
while (str != null)
{
sw.WriteLine(str);
           str = sr.ReadLine();
}
  
// to close the read stream
       sr.Close();
}
sw.Flush();
// to close the write stream
sw.Close();
}   
}
}
}

Please refer to the below screenshots to understand the indentation of the code: