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Files Operations

 

Routine Operations on Files

 

Opening a File

As opposed to creating a file, probably the second most regular operation performed on a file consists of opening it to read or explore its contents. To support opening a file, the FileInfo class is equipped with the Open() method that is overloaded with three versions.

If you have a text-based file and want to directly read from it, you can use the StreamReader class that is equipped with the Read() and the ReadLine() methods. As done for the StreamWriter class, after using a StreamReader object, make sure you close it.

 

Deleting a File

If you have an existing file you don't need anymore, you can delete it. This operation can be performed by calling the FileInfo::Delete() method. Its syntax is:

public:
    virtual void Delete() override;

Here is an example:

FileInfo ^ fleMembers = gcnew FileInfo(L"First.txt");
fleMembers->Delete();

Copying a File

You can make a copy of a file from one directory to another. To do this, you can call the FileInfo::CopyTo() method that is overloaded with two versions. The first version has the following syntax:

public:
    FileInfo ^ CopyTo(String ^ destFileName);

When calling this method, specify the path or directory that will be the destination of the copied file. Here is an example:

FileInfo ^ fleMembers = gcnew FileInfo(L"Reality.txt");
String ^ strMyDocuments =
    Environment.GetFolderPath(Environment::SpecialFolder::Personal);
fleMembers->CopyTo(String.Concat(strMyDocuments, "\\Federal.txt"));

In this example, a file named Reality.txt in the directory of the project would be retrieved and its content would be applied to a new file named Federal.txt created in the My Documents folder of the current user.

When calling the first version of the FileInfo::CopyTo() method, if the file exists already, the operation would not continue and you would simply receive a message box. If you insist, you can overwrite the target file. To do this, you can use the second version of this method. Its syntax is:

public:
    FileInfo ^ CopyTo(String ^destFileName, bool overwrite);

The first argument is the same as that of the first version of the method. The second argument specifies what action to take if the file exists already in the target directory. If you want to overwrite it, pass the argument as true; otherwise, pass it as false.

Moving a File

If you copy a file from one directory to another, you would have two copies of the same file or the same contents in two files. Instead of copying, if you want, you can simply move the file from one directory to another. This operation can be performed by calling the FileInfo::MoveTo() method. Its syntax is:

public:
    void MoveTo(String ^destFileName);

The argument to this method is the same as that of the CopyTo() method. After executing this method, the FileInfo object would be moved to the destFileName path.

Here is an example:

FileInfo ^ fleMembers = gcnew FileInfo(L"pop.txt");
String ^ strMyDocuments = Environment::GetFolderPath(Environment::SpecialFolder::Personal);
fleMembers->CopyTo(String::Concat(strMyDocuments, "\\pop.txt"));

Characteristics of a File

 

The Date and Time a File Was Created 

To keep track of it, after a file has been created, the operating system makes a note of the date and the time the file was created. This information can be valuable in other operations such as search routines. You too are allowed to change this date and time values to those you prefer.

As mentioned already, the OS makes sure to keep track of the date and time a file was created. To find out what those date and time values are, you can access the get accessor of the FileSystemInfo::CreationTime property. This would be done as follows:

DateTime dteCreationTime = fleLoan->CreationTime;
Console::WriteLine(L"Date and Time Created: " + dteCreationTime.ToString());

Of course, by entering the appropriate format in the parentheses of the ToString() method, you can get only either the date or only the time.

If you don't like the date, the time, or both, that the OS would have set when the file was created, you can change them. To change one or both of these values, you can assign a desired DateTime object to the set accessory of the FileSystemInfo::CreationTime property.

The Date and Time a File Was Last Accessed 

Many applications allow a user to open an existing file and to modify it. When people work in a team or when a particular file is regularly opened, at one particular time, you may want to know the date and time that the file was last accessed. To get this information, you can access the FileSystemInfo::LastAccessTime property.

If you are interested to know the last date and time a file was modified, you can get the value of its FileSystemInfo.LastWriteTime property.

The Name of a File

The operating system requires that each file have a name. In fact, the name must be specified when creating a file. This allows the OS to catalogue the computer files. This also allows you to locate or identify a particular file you need.

When reviewing or opening a file, to get its name, the FileInfo class is equipped with the Name property. Here is an example:

Console::WriteLine(L"The name of this file is: \"" + fleLoan->Name + "\"");

This string simply identifies a file.

The Extension of a File

With the advent of Windows 95 and later, the user doesn't have to specify the extension of a file when creating it. Because of the type of confusion that this can lead to, most applications assist the user with this detail. Some applications allow the user to choose among various extensions. For example, using Notepad, a user can open a text, a PHP, a script, or an HTML file.

When you access a file or when the user opens one, to know the extension of the file, you can access the value of the FileSystemInfo::Extension property. Here is an example:

Console::WriteLine(L"File Extension: " + fleLoan->Extension);

The Size of a File

One of the routine operations the operating system performs consists of calculating the size of files it holds. This information is provided in terms of bits, kilobits, or kilobytes. To get the size of a file, the FileInfo class is quipped with the Length property. Here is an example of accessing it:

Console::WriteLine(L"File Size: " + fleLoan::Length.ToString());

The Path to a File

Besides the name of the file, it must be located somewhere. The location of a file is referred to as its path or directory. The FileInfo class represents this path as the DirectoryName property. Therefore, if a file has already been created, to get its path, you can access the value of the FileInfo::DirectoryName property.

Besides the FileInfo::Directoryname, to know the full path to a file, you can access its FileSystemInfo::FullName property.

The Attributes of a File

Attributes are characteristics that apply to a file, defining what can be done or must be disallowed on it. The Attributes are primarily defined by, and in, the operating system, mostly when a file is created. When the user accesses or opens a file, to get its attributes, you can access the value of its FileSystemInfo::Attributes property. This property produces a FileAttributes object.

When you create or access a file, you can specify or change some of the attributes. To do this, you can a FileAttributes object and assign it to the FileSystemInfo.Attributes property.

FileAttributes is an enumerator with the following members: Archive, Compressed, Device, Directory, Encrypted, Hidden, Normal, NotContentIndexed, Offline, ReadOnly, ReparsePoint, SparseFile, System, and Temporary.

Directories

 

Introduction

A directory is a section of a medium (floppy disc, flash drive, hard drive, CD, DVD, etc) used to delimit a group of files. Because it is a "physical" area, it can handle operations not available on files. In fact, there are many fundamental differences between both:

  • A file is used to contain data. A directory doesn't contain data
  • A directory can contain one or more files and not vice-versa
  • A directory can contain other directories
  • A file can be moved from one directory to another. This operation is not possible vice-versa since a file cannot contain a directory

The similarities of both types are:

  • A directory or a file can be created. One of the restrictions is that two files cannot have the same name inside of the same directory. Two directories cannot have the same name inside of the same parent directory.
  • A directory or a file can be renamed. If a directory is renamed, the "path" of its file(s) changes
  • A directory or a file can be deleted. If a directory is deleted, its files are deleted also
  • A directory or a file can be moved. If a directory moves, it "carries" all of its files to the new location
  • A directory or a file can be copied. A file can be copied from one directory to another. If a directory is copied to a new location, all of its files are also copied to the new location

Practical LearningPractical Learning: Introducing Directories

  1. Start Microsoft Visual C++ 2005 Professional or Microsoft Visual C++ 2005 Express Edition
  2. To create a new application, on the main menu, click File -> New -> Project...
  3. In the Templates list, click Windows Forms Application
  4. Set the name to WattsALoan2 and click OK
  5. To be able to use the Visual Basic library, in the Solution Explorer, right-click WattsALoan2 and click References...
  6. Click Add New Reference...
  7. In the .NET property page, click Microsoft.VisualBasic
     
  8. Click OK and OK
  9. In the Common Controls section of the Toolbox, click ToolTip and click the form
  10. Design the form as follows:
     
    Watts' A Loan
    Control Name Text ToolTip on toolTip1
    Label   If this is a new loan, enter a new account number and the name of the customer who is requesting the loan  
    Label   To open a previously prepared loan, enter its account number and press Tab  
    Label   Acnt #:  
    Label   Customer Name:  
    Label   Customer:  
    TextBox txtAccountNumber   Account number of the customer requesting the loan
    TextBox txtCustomerName   Name of the customer requesting the loan
    Label   Empl #:  
    Label   Employee Name:  
    Label   Prepared By:  
    TextBox txtEmployeeNumber   Employee number of the clerk preparing the loan
    TextBox txtEmployeeName   Name of the clerk preparing the loan
    Button btnNewEmployee   Used to add a new employee to the company
    Button btnNewCustomer   Used to create an account for a new customer
    Label   Loan Amount:  
    TextBox txtLoanAmount   Amount of loan the customer is requesting
    Label   Interest Rate:  
    TextBox txtInterestRate   Annual percentage rate of the loan
    Label   %  
    Label   Periods  
    TextBox   txtPeriods The number of months the loan is supposed to last
    Button btnCalculate Calculate Used to calculate the monthly payment
    Label   Monthly Payment:  
    TextBox txtMonthlyPayment   The minimum amount the customer should pay every month
    Button btnClose Close Used to close the form
  11. Double-click the Calculate button and implement its event as follows:
     
    System::Void btnCalculate_Click(System::Object^  sender, System::EventArgs^  e)
    {
        double LoanAmount, InterestRate, Periods, MonthlyPayment;
    
        try {
    	 LoanAmount = double::Parse(txtLoanAmount->Text);
        }
        catch(FormatException ^)
        {
    	 MessageBox::Show(L"Invalid Loan Amount");
        }
    				 
        try {
    	 InterestRate = double::Parse(txtInterestRate->Text);
        }
        catch(FormatException ^)
        {
    	 MessageBox::Show(L"Invalid Interest Rate");
        }
    				 
        try {
    	 Periods = double::Parse(txtPeriods->Text);
        }
        catch(FormatException ^)
        {
    	 MessageBox::Show(L"Invalid Periods Value");
        }
    				 
        try {
    	 MonthlyPayment =
    	     Microsoft::VisualBasic::Financial::Pmt(InterestRate / 12 / 100,
    		                                Periods,
    						-LoanAmount,
    						0 ,
    				Microsoft::VisualBasic::DueDate::BegOfPeriod);
    	 txtMonthlyPayment->Text = MonthlyPayment.ToString(L"F");
        }
        catch(FormatException ^)
        {
    	 MessageBox::Show(L"Invalid Periods Value");
        }
    }
  12. Return to the form and double-click the Close button to implement its event as follows:
     
    System::Void btnClose_Click(System::Object^  sender, System::EventArgs^  e)
    {
        Close();
    }
  13. Scroll up completely and, under the other using lines, type using namespace System::IO;
  14. To create a new form, on the main menu, click Project -> Add New Item...
  15. In the Templates list, click Windows Form
  16. Set the Name to NewEmployee and click Add
  17. Design the form as follows:
     
    Control Text Name
    Label Employee #:
    TextBox txtEmployeeNumber
    Label Employee Name:
    TextBox txtEmployeeName
    Button Create btnCreate
    Button Close btnClose
  18. Double-click the Close button
  19. In the top section of the file, under the using using lines, type
    using namespace System::IO;
  20. Implement its event as follows:
     
    System::Void btnClose_Click(System::Object^  sender, System::EventArgs^  e)
    {
    	 Close();
    }
  21. Access the Form1 form
  22. Double-click the New button
  23. In the top section of the file, under the #pragma once line, type
     
    #include "NewEmployee.h"
  24. Scroll down and implement the event as follows:
     
    System::Void btnNewEmployee_Click(System::Object^  sender, System::EventArgs^  e)
    {
        NewEmployee ^ frmNewEmployee = gcnew NewEmployee;
    
        frmNewEmployee->ShowDialog();
    }
  25. Return to the form

Directory Creation

Before using a directory, you must first have it. You can use an existing directory if the operating system or someone else had already created one. You can also create a new directory. Directories are created and managed by various classes but the fundamental class is Directory. Directory is an abstract and sealed class. All of its methods are static, which means you will never need to declare an instance of the Directory class in order to use it.

Besides the Directory class, additional operations of folders and sub-folders can be performed using the DirectoryInfo class.

To create a directory, you can call the CreateDirectory() method of the Directory class. This method is available in two versions. One of the versions uses the following syntax:

public:
    static DirectoryInfo ^ CreateDirectry(String ^path);

This method takes as argument the (complete) path of the desired directory. Here is an example:

E:\Programs\Business Orders\Customer Information

When this method is called:

  1. It first checks the parent drive, in this case E.
    If the drive doesn't exist, because this method cannot create a drive, the compiler would throw a DirectoryNotFoundException exception
  2. If the drive (in this case E) exists, the compiler moves to the first directory part of the path; in this case this would be the Programs folder in the E drive.
    If the folder doesn't exist, the compiler would create it. If that first director doesn't exist, this means that the other directory(ies), if any, under the first don't exist. So, the compiler would create it/them
  3. If the first directory exists and if there is no other directory under that directory, the compiler would stop and would not do anything further.
  4. If the directory exists and there is a sub-directory specified under it, the compiler would check the existence of that directory.
    If the sub-directory exists, the compiler would not do anything further and would stop.
    If the sub-directory doesn't exist, the compiler would create it
  5. The compiler would repeat step 4 until the end of the specified path

The Directory::CreateDirectory() method returns a DirectoryInfo object that you can use as you see fit.

 

Practical LearningPractical Learning: Creating a Directory

  1. On the (main) form, double-click an unoccupied area of its body
  2. Implement its Load event as follows:
     
    System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e)
    {
    	 String ^ strDirectory = L"C:\\Watts A Loan";
    
    	 if( !Directory::Exists(strDirectory) )
    		 Directory::CreateDirectory(strDirectory);
    
    	 String ^ strFilename = strDirectory + L"\\Employees.wal";
    
    	 FileInfo ^ fiEmployees = gcnew FileInfo(strFilename);
    
    	 // If the employees file was not created already,
    	 // then create it
    	 if( !fiEmployees->Exists )
    	 {
    	     StreamWriter ^ stwEmployees = fiEmployees->CreateText();
    
    	     // And create a John Doe employee
    	    try {
    		 stwEmployees->WriteLine(L"00-000");
    		 stwEmployees->WriteLine(L"John Doe");
    	    }
    	    finally
    	    {
    		 stwEmployees->Close();
    	    }
    	 }
    }
  3. Display the NewEmployee form and double-click its Create button
  4. Implement its Click event as follows:
     
    System::Void btnCreate_Click(System::Object^  sender, System::EventArgs^  e)
    {
    	 String ^ strFilename = L"C:\\Watts A Loan\\Employees.wal";
    	 FileInfo ^ fiEmployees = gcnew FileInfo(strFilename);
    	 StreamWriter ^ stwEmployees = nullptr;
    
    	 // Normally, we should have the file already but just in case...
    	 if( !fiEmployees->Exists )
    		 stwEmployees = fiEmployees->CreateText();
    	 else // If the file exists already, then we will only add to it
    		 stwEmployees= fiEmployees->AppendText();
    				 
    	 try {
    		 stwEmployees->WriteLine(txtEmployeeNumber->Text);
    		 stwEmployees->WriteLine(txtEmployeeName->Text);
    	 }
    	 finally
    	 {
    		 stwEmployees->Close();
    	 }
    
    	 txtEmployeeNumber->Text = L"";
    	 txtEmployeeName->Text = L"";
    	 txtEmployeeNumber->Focus();
    }
  5. Return to the (main) form

Checking for a Directory Existence

Before using or creating a directory, you can first check if it exists. This is because, if a directory already exists in the location where you want to create it, you would be prevented from creating one with the same name. In the same way, if you just decide to directly use a directory that doesn't exist, the operation you want to perform may fail because the directory would not be found.

To check whether a directory exists or not, you can call the Directory::Exists() Boolean static method. Its syntax is:

public:
    static bool Exists(String ^path);

This method receives the (complete) path of the directory. If the path exists, the method returns true. If the directory doesn't exist, the method returns false.

To create a directory, you can call the CreateDirectory() method of the Directory class.

Locating a File

One of the most routine operations performed in a directory consists of looking for a file. Both Microsoft Windows operating systems and the user's intuition have different ways of addressing this issue. The .NET Framework also provides its own means of performing this operation, through various techniques. You can start by checking the sub-directories and files inside of a main directory.

To look for files in a directory, the DirectoryInfo class can assist you with its GetFiles() method, which is overloaded with three versions.

Practical LearningPractical Learning: Using Directories and Files

  1. In the combo box on top of the Properties window, select txtAccountNumber
  2. In the Events section, double-click Leave and implement the event as follows:
     
    System::Void txtAccountNumber_Leave(System::Object^  sender, System::EventArgs^  e)
    {
        String ^ strPath = L"C:\\Watts A Loan";
    
        DirectoryInfo ^ diLoans =
             gcnew DirectoryInfo(strPath);
        array<FileInfo ^> ^ aryLoans = diLoans->GetFiles(L"*",
    		SearchOption::AllDirectories);
    
        String ^ strFilename = txtAccountNumber->Text + L".wal";
    	String ^ strFullname = strPath + L"none.wal";
        bool found = false;
    
        for each(FileInfo ^ fle in aryLoans)
        {
            if( fle->Name == strFilename )
            {
                found = true;
                strFullname = fle->FullName;
            }
        }
    
        if( found == true )
        {
            FileStream ^ stmLoans =
    			File::Open(strFullname,
                            FileMode::Open,
                            FileAccess::Read);
            BinaryReader ^ bnrLoans = gcnew BinaryReader(stmLoans);
    
    		txtAccountNumber->Text = bnrLoans->ReadString();
        txtCustomerName->Text = bnrLoans->ReadString();
        txtEmployeeNumber->Text = bnrLoans->ReadString();
        txtEmployeeName->Text = bnrLoans->ReadString();
        txtLoanAmount->Text = bnrLoans->ReadString();
        txtInterestRate->Text = bnrLoans->ReadString();
        txtPeriods->Text = bnrLoans->ReadString();
        txtMonthlyPayment->Text = bnrLoans->ReadString();
    
    	bnrLoans->Close();
    	stmLoans->Close();
        }
    }
  3. In the combo box on top of the Properties window, select txtEmployeeNumber
  4. On the Properties window, click the Events button and double-click Leave
  5. Implement the event as follows:
     
    System::Void txtEmployeeNumber_Leave(System::Object^  sender, System::EventArgs^  e)
    {
        String ^ strFilename = L"C:\\Watts A Loan\\Employees.wal";
        FileInfo ^ fiEmployees = gcnew FileInfo(strFilename);
    
        if(fiEmployees->Exists )
        {
    	 if( txtEmployeeNumber->Text == L"" )
    	 {
    		 txtEmployeeName->Text = L"";
    		 return;
    	 }
    	 else
    	 {
    		 StreamReader ^ strEmployees = fiEmployees->OpenText();
    		 String ^ strEmployeeNumber, ^ strEmployeeName;
    		 bool found = false;
    
    		 try {
    			 while( strEmployeeNumber = strEmployees->ReadLine() )
    			 {
    	  		     if( strEmployeeNumber == txtEmployeeNumber->Text )
    			     {
    				 strEmployeeName   = strEmployees->ReadLine();
    				 txtEmployeeName->Text = strEmployeeName;
    				 found = true;
    			     }
    			 }
    
    			 // When the application has finished checking the file
    		// if there was no employee with that number, let the user know
    			 if( found == false )
    			 {
    			 MessageBox::Show(L"No employee with that number was found");
    				 txtEmployeeName->Text = L"";
    				 txtEmployeeNumber->Focus();
    			 }
    		 }
    		 finally
    		 {
    			 strEmployees->Close();
    		 }
    	 }
        }
    }
  6. Return to the form and double-click the Save button
  7. Implement the event as follows:
     
    System::Void btnSave_Click(System::Object^  sender, System::EventArgs^  e)
    {
        String ^ strPath = L"C:\\Watts A Loan\\" + txtAccountNumber->Text + L".wal";
    
        FileStream ^ stmLoan = File::Create(strPath);
        BinaryWriter ^ bnwLoan =
                    gcnew BinaryWriter(stmLoan);
    
        bnwLoan->Write(txtAccountNumber->Text);
        bnwLoan->Write(txtCustomerName->Text);
        bnwLoan->Write(txtEmployeeNumber->Text);
        bnwLoan->Write(txtEmployeeName->Text);
        bnwLoan->Write(txtLoanAmount->Text);
        bnwLoan->Write(txtInterestRate->Text);
        bnwLoan->Write(txtPeriods->Text);
        bnwLoan->Write(txtMonthlyPayment->Text);
    
    	txtAccountNumber->Text = L"";
        txtCustomerName->Text = L"";
        txtEmployeeNumber->Text = L"";
        txtEmployeeName->Text = L"";
        txtLoanAmount->Text = L"";
        txtInterestRate->Text = L"";
        txtPeriods->Text = L"";
        txtMonthlyPayment->Text = L"";
    
    	txtAccountNumber->Focus();
    
    	bnwLoan->Close();
    	stmLoan->Close();
    }
  8. Execute the application to test it
  9. First create a few employees as follows:
     
    Employee # Employee Name
    42-806 Patricia Katts
    75-148 Helene Mukoko
    36-222 Frank Leandro
    42-808 Gertrude Monay
  10. Process a few loans
     
    Watts A Loan - Loan Preparation
     
    Watts A Loan - Loan Result
  11. Close the application
 
 

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