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File Streams
 

Fundamental File Streaming
 

Introduction to File Streaming

File streaming consists of performing one of the routine operations on a file, such as creating it or opening it. This basic operation can be performed using a class called FileStream. You can use a FileStream object to get a stream ready for processing. As one of the most complete classes of file processing of the .NET Framework, FileStream is equipped with all necessary properties and methods. To use it, you must first declare a variable of it. The class is equipped with nine constructors.

One of the constructors (the second) of the FileStream class has the following syntax:

public FileStream(string path, FileMode mode);

This constructor takes as its first argument the name or the file or its path. The second argument specifies the type of operation to perform on the file. Here is an example:

using System;
using System.IO;

class Exercise
{
	static int Main()
	{
		string NameOfFile = "Persons.spr";

		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Create);
		
		return 0;
	}
}

Practical Learning: Creating a Stream
  1. To create a new stream, access the IceCream.cs file and change the SaveOrder() method as follows:
      
    using System;
using System.IO;

namespace VendingMachine
{
	// This class is used to create and manage an ice cream
	// and to process an order
	sealed class IceCream
	{
		
		. . . No Change

		
		public void SaveOrder()
		{
			string NameOfFile;

		Console.Write("Please enter your initials or the name we " +
		"will use to remember your order: ");
			NameOfFile = Console.ReadLine();

	FileStream stmIceCream = new FileStream(NameOfFile, FileMode.Create);
			
			if( File.Exists(NameOfFile) )
			{
				. . . No Change
			}
			else
		Console.WriteLine("The name you entered is not registered " +
				  "in our previous orders");
		}

		public void OpenOrder()
		{
			. . . No Change
		}
	}
}
  2. Save the file

Stream Writing

A streaming operation is typically used to create a stream. Once the stream is ready, you can write data to it. The writing operation is perform through various classes. One of these classes is BinaryWriter.

The BinaryWriter class can be used to write values of primitive data types (char, int, float, double, etc). To use a BinaryWriter value, you can first declare its variable. To do this, you would use one of the class' three constructors. One of its constructors (the second) has the following syntax:

public BinaryWriter(Stream output);

This constructor takes as argument a Stream value, which could be a FileStream variable. Here is an example:

using System;
using System.IO;

class Exercise
{
	static int Main()
	{
		string NameOfFile = "Persons.spr";

		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Create);
		BinaryWriter wrtPersons = new BinaryWriter(fstPersons);

		return 0;
	}
}

Most classes that are used to add values to a stream are equipped with a method called Write. This is also the case for the BinaryWriter class. This method takes as argument the value that must be written to the stream. The method is overloaded so that there is a version for each primitive data type. Here is an example that adds strings to a newly created file:

using System;
using System.IO;

class Exercise
{
	static int Main()
	{
		string NameOfFile = "Persons.spr";

		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Create);
		BinaryWriter wrtPersons = new BinaryWriter(fstPersons);

		wrtPersons.Write("James Bloch");
		wrtPersons.Write("Catherina Wallace");
		wrtPersons.Write("Bruce Lamont");
		wrtPersons.Write("Douglas Truth");

		return 0;
	}
}

Stream Closing

When you use a stream, it requests resources from the operating system and uses them while the stream is available. When you are not using the stream anymore, you should free the resources and make them available again to the operating system so that other services can use them. This is done by closing the stream.

To close a stream, you can can call the Close() method of the class(es) you were using. Here are examples:

   
using System;
using System.IO;

class Exercise
{
	static int Main()
	{
		string NameOfFile = "Persons.spr";

		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Create);
		BinaryWriter wrtPersons = new BinaryWriter(fstPersons);

		wrtPersons.Write("James Bloch");
		wrtPersons.Write("Catherina Wallace");
		wrtPersons.Write("Bruce Lamont");
		wrtPersons.Write("Douglas Truth");
		
		wrtPersons.Close();
		fstPersons.Close();

		return 0;
	}
}

Practical Learning: Writing to a Stream
  1. To be able to complete a file, change the SaveOrder() method in the IceCream.cs file as follows:
      
    using System;
using System.IO;

namespace VendingMachine
{
	// This class is used to create and manage an ice cream
	// and to process an order
	sealed class IceCream
	{
		. . . No Change
		
		
		
		public void SaveOrder()
		{
			string NameOfFile;

			Console.WriteLine("Please enter your initials or the name we will use to remember your order: ");
			NameOfFile = Console.ReadLine();
			NameOfFile = NameOfFile + ".icr";

			// Find out if the user entered a name of a file that is already in the machine
			if( File.Exists(NameOfFile) )
			{
				char Answer;

				FileStream stmIceCream = new FileStream(NameOfFile, FileMode.Create);
				BinaryWriter bnwIceCream = new BinaryWriter(stmIceCream);

				// If so, find out if the user wants to replace the old file
				Console.WriteLine("The file you entered exists already.");
				Console.Write("Do you want to replace it(y/n)?" );
				Answer = char.Parse(Console.ReadLine());

				// If the customer wants to replace it...
				if( Answer == 'y' || Answer == 'Y' )
				{
					// ... do so
					Console.WriteLine("The former order with the same name will be replaced");

					Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
					Console.WriteLine(" Saving Order: {0}", NameOfFile);
					bnwIceCream.Write(Flavor[ChoiceFlavor-1]);
					bnwIceCream.Write(Container[ChoiceContainer-1]);
					bnwIceCream.Write(Ingredient[ChoiceIngredient-1]);
					bnwIceCream.Write(Scoops);
					bnwIceCream.Write(TotalPrice);
				}
				// If the customer wants to save the new order with a different name
				else if( Answer == 'n' || Answer == 'N' )
				{
					// Ask the user to enter a name to remember the order
					Console.Write("Please enter a name we will use to remember this order: ");
					NameOfFile = Console.ReadLine();
					NameOfFile = NameOfFile + ".icr";

					stmIceCream = new FileStream(NameOfFile, FileMode.Create);
					bnwIceCream = new BinaryWriter(stmIceCream);

					Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
					Console.WriteLine(" Saving Order: {0}", NameOfFile);
					bnwIceCream.Write(Flavor[ChoiceFlavor-1]);
					bnwIceCream.Write(Container[ChoiceContainer-1]);
					bnwIceCream.Write(Ingredient[ChoiceIngredient-1]);
					bnwIceCream.Write(Scoops);
					bnwIceCream.Write(TotalPrice);
				}
				else
					Console.WriteLine("Invalid Answer - We will close");
					bnwIceCream.Close();
					stmIceCream.Close();
			}
			else
			{
				FileStream stmIceCream = new FileStream(NameOfFile, FileMode.Create);
				BinaryWriter bnwIceCream = new BinaryWriter(stmIceCream);

				Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
				Console.WriteLine(" Saving Order: {0}", NameOfFile);
				bnwIceCream.Write(Flavor[ChoiceFlavor-1]);
				bnwIceCream.Write(Container[ChoiceContainer-1]);
				bnwIceCream.Write(Ingredient[ChoiceIngredient-1]);
				bnwIceCream.Write(Scoops);
				bnwIceCream.Write(TotalPrice);
			
				bnwIceCream.Close();
				stmIceCream.Close();
			}
		}

		public void OpenOrder()
		{
			. . . No Change
		}
	}
}
  2. Save the file and switch to the Command Prompt
  3. To compile it, type csc /out:"Ice Cream Vending Machine".exe IceCream.cs Exercise.cs and press Enter
  4. To execute it, type "Ice Cream Vending Machine" and press Enter. Here is an example:
      
    Have you ordered here before(y/n)? n

=-= Ice Cream Vending Machine =-=
 ------ New Customer Order ------
What type of flavor do you want?
1 - Vanilla
2 - Cream of Cocoa
3 - Chocolate Chip
4 - Organic Strawberry
5 - Butter Pecan
6 - Cherry Coke
7 - Chocolate Brownies
8 - Caramel Au Lait
9 - Chunky Butter
10 - Chocolate Cookie
Your Choice? 7
What type of container do you want?
1 - Cone
2 - Cup
3 - Bowl
Your Choice? 1
Do you want an ingredient or not
1 - No Ingredient
2 - Peanuts
3 - M & M
4 - Cookies
Your Choice? 4
How many scoops(1, 2, or 3)? 2

Ice Cream Order
Flavor:      Chocolate Brownies
Container:   Cone
Ingredient:  Cookies
Scoops:      2
Total Price: $3.10

Do you want us to remember this order the next time you come to get your ice scr
eam (y/n)? y
Please enter your initials or the name we will use to remember your order:
Jane44

=-= Ice Cream Vending Machine =-=
 Saving Order: Jane44.icr
  5. Return to the IceCream.cs file

Stream Reading

As opposed to writing to a stream, you may want to read existing data from it. Before doing this, you can first specify your intent to the streaming class using the FileMode enumerator. This can be done using the FileStream class as follows:

using System;
using System.IO;

class Exercise
{
	static int Main()
	{
		string NameOfFile = "Persons.spr";
/*
		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Create);
		BinaryWriter wrtPersons = new BinaryWriter(fstPersons);

		wrtPersons.Write("James Bloch");
		wrtPersons.Write("Catherina Wallace");
		wrtPersons.Write("Bruce Lamont");
		wrtPersons.Write("Douglas Truth");
		
		wrtPersons.Close();
		fstPersons.Close();
*/
		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Open);

		return 0;
	}
}

Once the stream is ready, you can get prepared to read data from it. To support this, you can use the BinaryReader class. This class provides two constructors. One of the constructors (the first) has the following syntax:

public BinaryReader(Stream input);

This constructor takes as argument a Stream value, which could be a FileStream object. After declaring a FileStream variable using this constructor, you can read data from it. To do this, you can call an appropriate method. This class provides an appropriate method for each primitive data type.

After using the stream, you should close it to reclaim the resources it was using. This is done by calling the Close() method.

Here is an example of using the mentioned methods:

using System;
using System.IO;

class Exercise
{
	static int Main()
	{
		string NameOfFile = "Persons.spr";
/*
		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Create);
		BinaryWriter wrtPersons = new BinaryWriter(fstPersons);

		wrtPersons.Write("James Bloch");
		wrtPersons.Write("Catherina Wallace");
		wrtPersons.Write("Bruce Lamont");
		wrtPersons.Write("Douglas Truth");
		
		wrtPersons.Close();
		fstPersons.Close();
*/
		FileStream fstPersons = new FileStream(NameOfFile, FileMode.Open);
		BinaryReader rdrPersons = new BinaryReader(fstPersons);
		string strLine = null;

		strLine = rdrPersons.ReadString();
		Console.WriteLine(strLine);
		strLine = rdrPersons.ReadString();
		Console.WriteLine(strLine);
		strLine = rdrPersons.ReadString();
		Console.WriteLine(strLine);
		strLine = rdrPersons.ReadString();
		Console.WriteLine(strLine);

		rdrPersons.Close();
		fstPersons.Close();

		return 0;
	}
}

Practical LearningPractical Learning: Reading From a Stream
  1. To be able to retrieve data from an existing file, change the OpenFile() method as follows:
     
    Source File: IceCream.cs 
    using System;
using System.IO;

namespace VendingMachine
{
	// This class is used to create and manage an ice cream
	// and to process an order
	sealed class IceCream
	{
		// This is the base price of an ice cream
		// Optional values may be added to it
		public const decimal BasePrice = 1.55M;

		// These arrays are used to build the components of various ice creams
		// In C#, we can allocate an array's memory in the body of the class
		private string[] Flavor;
		private string[] Container;
		private string[] Ingredient;

		// Additional factor used to process an ice cream order
		private int Scoops;
		private decimal TotalPrice;

		// Variables that will hold the user's choice
		// These are declared "globally" so they can be shared among methods
		int ChoiceFlavor;
		int ChoiceContainer;
		int ChoiceIngredient;

		// This default constructor is the best place for us to initialize the array
		public IceCream()
		{
			Flavor = new string[10];	
			Flavor[0] = "Vanilla";
			Flavor[1] = "Cream of Cocoa";
			Flavor[2] = "Chocolate Chip";
			Flavor[3] = "Organic Strawberry";
			Flavor[4] = "Butter Pecan";
			Flavor[5] = "Cherry Coke";
			Flavor[6] = "Chocolate Brownies";
			Flavor[7] = "Caramel Au Lait";
			Flavor[8] = "Chunky Butter";
			Flavor[9] = "Chocolate Cookie";

			Ingredient = new string[4];
			Ingredient[0] = "No Ingredient";
			Ingredient[1] = "Peanuts";
			Ingredient[2] = "M & M";
			Ingredient[3] = "Cookies";

			Container  = new string[3];
			Container[0] = "Cone";
			Container[1] = "Cup";
			Container[2] = "Bowl";
		}

		// This method requests a flavor from the user and returns the choice
		public void ChooseFlavor()
		{
			// Make sure the user selects a valid number that represents a flavor...
			do 
			{
				// In case the user types a symbol that is not a number
				try 
				{
					Console.WriteLine("What type of flavor do you want?");
					for(int i = 0; i < Flavor.Length; i++)
						Console.WriteLine("{0} - {1}", i+1, Flavor[i]);
					Console.Write("Your Choice? " );
					ChoiceFlavor = int.Parse(Console.ReadLine());
				}
				catch(FormatException)	// display an appropriate message
				{
					Console.WriteLine("You must enter a valid number and no other character!");
				}
		
				// If the user typed an invalid number out of the allowed range
				// let him or her know and provide another chance
				if( ChoiceFlavor < 1 || ChoiceFlavor > Flavor.Length )
					Console.WriteLine("Invalid Choice - Try Again!\n");
			} while( ChoiceFlavor < 1 || ChoiceFlavor > Flavor.Length );
		}

		// This method allows the user to select a container
		public void ChooseContainer()
		{
			// Make sure the user selects a valid number that represents a container
			do 
			{
				// If the user types a symbol that is not a number
				try 
				{
					Console.WriteLine("What type of container do you want?");
					for(int i = 0; i < Container.Length; i++)
						Console.WriteLine("{0} - {1}", i+1, Container[i]);
					Console.Write("Your Choice? ");
					ChoiceContainer = int.Parse(Console.ReadLine());
				}
				catch(FormatException)	// display an appropriate message
				{
					Console.WriteLine("You must enter a valid number and no other character!");
				}
			
				// If the user typed an invalid number out of the allowed range
				// let him or her know and provide another chance
				if( ChoiceContainer < 1 || ChoiceContainer > Container.Length )
					Console.WriteLine("Invalid Choice - Try Again!");
			} while( ChoiceContainer < 1 || ChoiceContainer > Container.Length );
		}

		public void ChooseIngredient()
		{
			do 
			{
				try 
				{
					Console.WriteLine("Do you want an ingredient or not");
					for(int i = 0; i < Ingredient.Length; i++)
						Console.WriteLine("{0} - {1}", i+1, Ingredient[i]);
					Console.Write("Your Choice? ");
					ChoiceIngredient = int.Parse(Console.ReadLine());
				}
				catch(FormatException)
				{
					Console.WriteLine("You must enter a valid number and no other character!");
				}

				if( ChoiceIngredient < 1 || ChoiceIngredient > Ingredient.Length )
					Console.WriteLine("Invalid Choice - Try Again!");
			} while( ChoiceIngredient < 1 || ChoiceIngredient > Ingredient.Length );
		}

		public void SpecifyNumberOfScoops()
		{
			do
			{
				try 
				{
					Console.Write("How many scoops(1, 2, or 3)? ");
					Scoops = int.Parse(Console.ReadLine());
				}
				catch(FormatException)
				{
					Console.WriteLine("You must enter a valid number and no other character!");
				}

				if( Scoops < 1 || Scoops > 3 )
					Console.WriteLine("Invalid Choice - Try Again!");
			} while( Scoops < 1 || Scoops > 3 );
		}

		// This method is used to process a customer order
		// It uses the values of the above methods
		public void ProcessAnOrder()
		{
			//			int ChoiceFlavor;
			//			int ChoiceContainer;
			//			int ChoiceIngredient;
			decimal PriceIngredient, PriceScoop;

			// Let the user know that this is a vending machine
			Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
			Console.WriteLine(" ------ New Customer Order ------");

			// Let the user select the components of the ice cream
			ChooseFlavor();
			ChooseContainer();
			ChooseIngredient();
			SpecifyNumberOfScoops();

			// If the user selects an ingredient instead of "No Ingredient",
			// add $0.50 to the order
			if( ChoiceIngredient == 2 || ChoiceIngredient == 3 || ChoiceIngredient == 4 )
				PriceIngredient = 0.50M;
			else
				PriceIngredient = 0.00M;

			// Instead of multiplying a number scoops to a value,
			// We will use an incremental value depending on the number of scoops
			if( Scoops == 1 )
				PriceScoop = 0.65M;
			else if( Scoops == 2 )
				PriceScoop = 1.05M;
			else
				PriceScoop = 1.55M;

			// Calculate the total price of the ice cream
			TotalPrice = BasePrice + PriceScoop + PriceIngredient;

			// Create the ice cream...

			// And display a receipt to the user
			DisplayReceipt();
		}

		// This method is used to display a receipt to the user
		public void DisplayReceipt()
		{
			Console.WriteLine("\nIce Cream Order");
			Console.WriteLine("Flavor:      {0}", Flavor[ChoiceFlavor-1]);
			Console.WriteLine("Container:   {0}", Container[ChoiceContainer-1]);
			Console.WriteLine("Ingredient:  {0}", Ingredient[ChoiceIngredient-1]);
			Console.WriteLine("Scoops:      {0}", Scoops);
			Console.WriteLine("Total Price: {0:C}\n", TotalPrice);
		}
		
		public void SaveOrder()
		{
			string NameOfFile;

			Console.WriteLine("Please enter your initials or the name we will use to remember your order: ");
			NameOfFile = Console.ReadLine();
			NameOfFile = NameOfFile + ".icr";

			// Find out if the user entered a name of a file that is already in the machine
			if( File.Exists(NameOfFile) )
			{
				char Answer;

				FileStream stmIceCream = new FileStream(NameOfFile, FileMode.Create);
				BinaryWriter bnwIceCream = new BinaryWriter(stmIceCream);

				// If so, find out if the user wants to replace the old file
				Console.WriteLine("The file you entered exists already.");
				Console.Write("Do you want to replace it(y/n)?" );
				Answer = char.Parse(Console.ReadLine());

				// If the customer wants to replace it...
				if( Answer == 'y' || Answer == 'Y' )
				{
					// ... do so
					Console.WriteLine("The former order with the same name will be replaced");

					Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
					Console.WriteLine(" Saving Order: {0}", NameOfFile);
					bnwIceCream.Write(Flavor[ChoiceFlavor-1]);
					bnwIceCream.Write(Container[ChoiceContainer-1]);
					bnwIceCream.Write(Ingredient[ChoiceIngredient-1]);
					bnwIceCream.Write(Scoops);
					bnwIceCream.Write(TotalPrice);
				}
				// If the customer wants to save the new order with a different name
				else if( Answer == 'n' || Answer == 'N' )
				{
					// Ask the user to enter a name to remember the order
					Console.Write("Please enter a name we will use to remember this order: ");
					NameOfFile = Console.ReadLine();
					NameOfFile = NameOfFile + ".icr";

					stmIceCream = new FileStream(NameOfFile, FileMode.Create);
					bnwIceCream = new BinaryWriter(stmIceCream);

					Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
					Console.WriteLine(" Saving Order: {0}", NameOfFile);
					bnwIceCream.Write(Flavor[ChoiceFlavor-1]);
					bnwIceCream.Write(Container[ChoiceContainer-1]);
					bnwIceCream.Write(Ingredient[ChoiceIngredient-1]);
					bnwIceCream.Write(Scoops);
					bnwIceCream.Write(TotalPrice);
				}
				else
					Console.WriteLine("Invalid Answer - We will close");
					bnwIceCream.Close();
					stmIceCream.Close();
			}
			else
			{
				FileStream stmIceCream = new FileStream(NameOfFile, FileMode.Create);
				BinaryWriter bnwIceCream = new BinaryWriter(stmIceCream);

				Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
				Console.WriteLine(" Saving Order: {0}", NameOfFile);
				bnwIceCream.Write(Flavor[ChoiceFlavor-1]);
				bnwIceCream.Write(Container[ChoiceContainer-1]);
				bnwIceCream.Write(Ingredient[ChoiceIngredient-1]);
				bnwIceCream.Write(Scoops);
				bnwIceCream.Write(TotalPrice);
			
				bnwIceCream.Close();
				stmIceCream.Close();
			}
		}

		public void OpenOrder()
		{
			string NameOfFile;
		
			string SelectedFlavor;
			string SelectedContainer;
			string SelectedIngredient;

			// Ask the user to enter a name of a previously saved order
			Console.Write("Please enter the name you previously gave to remember your order: ");
			NameOfFile = Console.ReadLine();
			NameOfFile = NameOfFile + ".icr";

			FileStream stmIceCream = new FileStream(NameOfFile, FileMode.Open);
			BinaryReader bnrIceCream = new BinaryReader(stmIceCream);

			// Find out if this order was previously saved in the machine
			if( File.Exists(NameOfFile) )
			{
				// If so, open it
				SelectedFlavor = bnrIceCream.ReadString();
				SelectedContainer = bnrIceCream.ReadString();
				SelectedIngredient = bnrIceCream.ReadString();
				Scoops = bnrIceCream.ReadInt32();
				TotalPrice = bnrIceCream.ReadDecimal();

				// And display it to the user
				Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
				Console.WriteLine(" Previous Order: {0}", NameOfFile);
				Console.WriteLine("Flavor:      {0}", SelectedFlavor);
				Console.WriteLine("Container:   {0}", SelectedContainer);
				Console.WriteLine("Ingredient:  {0}", SelectedIngredient);
				Console.WriteLine("Scoops:      {0}", Scoops);
				Console.WriteLine("Total Price: {0:C}\n", TotalPrice);

				bnrIceCream.Close();
				stmIceCream.Close();
			}
			else
				Console.WriteLine("The name you entered is not registered in our previous orders");
		}
	}
}
    Source File: Exercise.cs 
    using System;

class Exercise
{
	static int Main()
	{
		VendingMachine.IceCream IS = new VendingMachine.IceCream();
		char Answer = 'n';

		Console.Write("Have you ordered here before(y/n)? ");
		Answer = char.Parse(Console.ReadLine());

		if( Answer == 'y' || Answer == 'Y' )
			IS.OpenOrder();
		else
		{
			IS.ProcessAnOrder();

			Console.Write("Do you want us to remember this order the next time you come to get your ice cream (y/n)? ");
			Answer = char.Parse(Console.ReadLine());

			if( Answer == 'y' || Answer == 'Y' )
				IS.SaveOrder();
		}

		return 0;
	}
}
  2. Save the file and switch to the Command Prompt
  3. To compile it, type csc /out:"Ice Cream Vending Machine".exe IceCream.cs Exercise.cs and press Enter
  4. To execute it, type "Ice Cream Vending Machine" and press Enter. Here is an example:
      
    Have you ordered here before(y/n)? y
Please enter the name you previously gave to remember your order: Jane44

=-= Ice Cream Vending Machine =-=
 Previous Order: Jane44.icr
Flavor:      Chocolate Brownies
Container:   Cone
Ingredient:  Cookies
Scoops:      2
Total Price: $3.10
  5. Return to the IceCream.cs file
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