Binary File Streaming

Introduction to File Streaming

File streaming consists of performing one of the routine operations on a file, such as creating 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 of the file or its path. The second argument specifies the type of operation to perform on the file. Here is an example:

void StartProcessing(Object *o, EventArgs *e)
{
	String *fileName = S"Persons.spr";

	FileStream *fstPersons = new FileStream(fileName, FileMode::Create);
}

1. Create a new Windows Forms Application named ROSH1
2. Design the form as follows:
    

   Control Name Text Other Properties GroupBox   Identification   Label   Student Name:   TextBox txtStudentName     Label   School Year:   TextBox txtSchoolYear1     Label   /   TextBox txtSchoolYear2     GroupBox   Grades   Label   English:   TextBox txtEnglish 0.00   Label   History:   TextBox txtHistory 0.00   Label   Economics:   TextBox txtEconomics 0.00   Label   2nd Language:   TextBox txt2ndLanguage 0.00   Label   Geography:   TextBox txtGeography 0.00   Label   Arts:   TextBox txtArts 0.00   Label   Math:   TextBox txtMath 0.00   Label   Science:   TextBox txtScience 0.00   Label   Phys Educ:   TextBox txtPhysEduc 0.00   GroupBox   Grade Processing   Button btnCalculate Calculate   Label   Total:   TextBox txtTotal 0.00   Label   Average:   TextBox txtAverage 0.00   Button btnSave Save   Button btnOpen Open   Button btnClose Close

3. Double-click the Calculate button and implement its Click event as follows:
    

   System::Void btnCalculate_Click(System::Object * sender, System::EventArgs * e) { double english, history, economics, language2, geography, arts, math, science, physEduc, total, average; // Retrieve the value entered for each course try { english = this->txtEnglish->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the English course is not valid"); this->txtEnglish->Focus(); } try { history = this->txtHistory->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the History course is not valid"); this->txtEnglish->Focus(); } try { economics = this->txtEconomics->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the Economics course is not valid"); this->txtEnglish->Focus(); } try { language2 = this->txt2ndLanguage->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the 2nd Language course is not valid"); this->txtEnglish->Focus(); } try { geography = this->txtGeography->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the Geography course is not valid"); this->txtEnglish->Focus(); } try { arts = this->txtArts->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the Arts course is not valid"); this->txtEnglish->Focus(); } try { math = this->txtMath->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the Math course is not valid"); this->txtEnglish->Focus(); } try { science = this->txtScience->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the Science course is not valid"); this->txtEnglish->Focus(); } try { physEduc = this->txtPhysEduc->Text->ToDouble(0); } catch(FormatException *) { MessageBox::Show(S"The value you entered for the Physical Education course is not valid"); this->txtEnglish->Focus(); } // Calculate the total and the average total = english + history + economics + language2 + geography + arts + math + science + physEduc; average = total / 9; // Display the total and the average this->txtTotal->Text = total.ToString(S"F"); this->txtAverage->Text = average.ToString(S"F"); }

4. Return to the form.
   Double-click the Close button and implement its event as follows:
    

   System::Void btnClose_Click(System::Object * sender, System::EventArgs * e) { Close(); }

5. Execute the application to test it

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 performed 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 pointer. To do this, you would use one of the class' three constructors. The first constructor is the default, meaning it doesn't take an argument. The second constructor 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:

void StartProcessing(Object *o, EventArgs *e)
{
	String *fileName = S"Persons.spr";

	FileStream *fstPersons = new FileStream(fileName, FileMode::Create);
	BinaryWriter *wrtPersons = new BinaryWriter(fstPersons);
}

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:

void StartProcessing(Object *o, EventArgs *e)
{
	String *fileName = S"Persons.spr";

	FileStream *fstPersons = new FileStream(fileName, FileMode::Create);
	BinaryWriter *wrtPersons = new BinaryWriter(fstPersons);

	wrtPersons->Write(S"James Bloch");
	wrtPersons->Write(S"Catherina Wallace");
	wrtPersons->Write(S"Bruce Lamont");
	wrtPersons->Write(S"Douglas Truth");
}

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:

void StartProcessing(Object *o, EventArgs *e)
{
	String *fileName = S"Persons.spr";

	FileStream *fstPersons = new FileStream(fileName, FileMode::Create);
	BinaryWriter *wrtPersons = new BinaryWriter(fstPersons);

	wrtPersons->Write(S"James Bloch");
	wrtPersons->Write(S"Catherina Wallace");
	wrtPersons->Write(S"Bruce Lamont");
	wrtPersons->Write(S"Douglas Truth");

	wrtPersons->Close();
	fstPersons->Close();
}

Practical Learning: Writing to a Stream

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:

void StartProcessing(Object *o, EventArgs *e)
{
	String *fileName = S"Persons.spr";
/*
	FileStream *fstPersons = new FileStream(fileName, FileMode::Create);
	BinaryWriter *wrtPersons = new BinaryWriter(fstPersons);

	wrtPersons->Write(S"James Bloch");
	wrtPersons->Write(S"Catherina Wallace");
	wrtPersons->Write(S"Bruce Lamont");
	wrtPersons->Write(S"Douglas Truth");

	wrtPersons->Close();
	fstPersons->Close();
*/
	FileStream *fstPersons = new FileStream(fileName, FileMode::Open);
}

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 support this, the 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:

Practical Learning: Reading From a Stream