SUMMARY
This step-by-step article shows you how to do six basic
file input/output (I/O) operations in Microsoft Visual C# 2005 or in Microsoft Visual C# .NET. If you are new to the Microsoft .NET Framework,
you will find that the object model for file operations in .NET is similar to
the
FileSystemObject (FSO) that is popular with many Microsoft Visual Studio 6.0 developers. To
make the transition easier, the functionality that is demonstrated in this
article is based on the following Microsoft Knowledge Base article:
186118 How to use FileSystemObject with Visual Basic
You can still use the
FileSystemObject in .NET. Because the
FileSystemObject is a Component Object Model (COM) component, .NET requires that
access to the object be through the Interop layer. .NET generates a wrapper for
the component for you if you want to use it. However, the
File,
FileInfo,
Directory,
DirectoryInfo classes, and other related classes in the .NET Framework, offer
functionality that is not available with the FSO, without the overhead of the
Interop layer.
Requirements
The following list outlines the recommended hardware, software, network infrastructure, and service packs that you need:
- Visual C# 2005 or Visual C# .NET
Demonstrated file I/O operations
The examples in this article describe basic file I/O operations.
The "Step-by-Step Example" section describes how to create a sample program
that demonstrates the following file I/O operations:
- Read a Text File
- Write a Text File
- View File Information
- List Disk Drives
- List Folders
- List Files
Note If you want to use the following code samples directly, be aware
of the following:
- You must include the System.IO namespace, as follows:
using System.IO;
- Declare the winDir variable as follows:
string winDir=System.Environment.GetEnvironmentVariable("windir");
- The addListItem function is declared as follows:
private void addListItem(string value)
{
this.listbox1.Items.Add(value);
}
Note Instead of declaring and using the addListItem function, you can use the following statement directly:
this.listbox1.Items.Add(value);"
Read a Text File
The following sample code uses a
StreamReader class to read the System.ini file. The contents of the file are
added to a
ListBox control. The
try...catch block is used to alert the program if the file is empty. There
are many ways to determine when the end of the file is reached; this sample
uses the
Peek method to examine the next line before reading it.
StreamReader reader=new StreamReader(winDir + "\\system.ini");
try
{
do
{
addListItem(reader.ReadLine());
}
while(reader.Peek() != -1);
}
catch
{
addListItem("File is empty");}
finally
{
reader.Close();
}
Write a Text File
This sample code uses a
StreamWriter class to create and write to a file. If you have an existing
file, you can open it in the same way.
StreamWriter writer = new StreamWriter("c:\\KBTest.txt");
writer.WriteLine("File created using StreamWriter class.");
writer.Close();
this.listbox1.Items.Clear();
addListItem("File Written to C:\\KBTest.txt");
View File Information
This sample code uses a
FileInfo object to access a file's properties. Notepad.exe is used in this
sample. The properties appear in a
ListBox control.
FileInfo FileProps =new FileInfo(winDir + "\\notepad.exe");
addListItem("File Name = " + FileProps.FullName);
addListItem("Creation Time = " + FileProps.CreationTime);
addListItem("Last Access Time = " + FileProps.LastAccessTime);
addListItem("Last Write TIme = " + FileProps.LastWriteTime);
addListItem("Size = " + FileProps.Length);
FileProps = null;
List Disk Drives
This sample code uses the
Directory and
Drive classes to list the logical drives on a system. For this sample,
the results appear in a
ListBox control.
string[] drives = Directory.GetLogicalDrives();
foreach(string drive in drives)
{
addListItem(drive);
}
List Subfolders
This sample code uses the
GetDirectories method of the
Directory class to get a list of folders.
string[] dirs = Directory.GetDirectories(winDir);
foreach(string dir in dirs)
{
addListItem(dir);
}
List Files
This sample code uses the
GetFiles method of the
Directory class to get a listing of files.
string[] files= Directory.GetFiles(winDir);
foreach (string i in files)
{
addListItem(i);
}
Many things can go wrong when a user gains access to files. The files
may not exist, the files may be in use, or users may not have rights on the
files or folders that they are trying to access. It is important to consider
these possibilities when you write code and to handle the exceptions that may
be generated.
Step-by-step example
- In Visual C# .NET or in Visual C# 2005, create a new Windows Application. By
default, Form1 is created.
- Open the code window for Form1.
- Delete all of the code in the Code-Behind
Editor.
- Paste the following code in the Code-Behind Editor window:
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.IO;
namespace fso_cs
{
/// <summary>
/// Summary description for Form1.
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.Button button1;
private System.Windows.Forms.Button button2;
private System.Windows.Forms.Button button3;
private System.Windows.Forms.Button button4;
private System.Windows.Forms.Button button5;
private System.Windows.Forms.Button button6;
string winDir=System.Environment.GetEnvironmentVariable("windir");
private System.Windows.Forms.ListBox listbox1;
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.Container components = null;
public Form1()
{
//
// Required for Windows Form Designer support.
//
InitializeComponent();
//
// TO DO: Add any constructor code after InitializeComponent call.
//
}
/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.button2 = new System.Windows.Forms.Button();
this.button3 = new System.Windows.Forms.Button();
this.listbox1 = new System.Windows.Forms.ListBox();
this.button4 = new System.Windows.Forms.Button();
this.button5 = new System.Windows.Forms.Button();
this.button6 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(216, 32);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(112, 23);
this.button1.TabIndex = 1;
this.button1.Text = "button1";
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// button2
//
this.button2.Location = new System.Drawing.Point(216, 64);
this.button2.Name = "button2";
this.button2.Size = new System.Drawing.Size(112, 23);
this.button2.TabIndex = 2;
this.button2.Text = "button2";
this.button2.Click += new System.EventHandler(this.button2_Click);
//
// button3
//
this.button3.Location = new System.Drawing.Point(216, 96);
this.button3.Name = "button3";
this.button3.Size = new System.Drawing.Size(112, 23);
this.button3.TabIndex = 3;
this.button3.Text = "button3";
this.button3.Click += new System.EventHandler(this.button3_Click);
//
// listbox1
//
this.listbox1.Location = new System.Drawing.Point(24, 24);
this.listbox1.Name = "listbox1";
this.listbox1.Size = new System.Drawing.Size(176, 199);
this.listbox1.TabIndex = 0;
//
// button4
//
this.button4.Location = new System.Drawing.Point(216, 128);
this.button4.Name = "button4";
this.button4.Size = new System.Drawing.Size(112, 23);
this.button4.TabIndex = 4;
this.button4.Text = "button4";
this.button4.Click += new System.EventHandler(this.button4_Click);
//
// button5
//
this.button5.Location = new System.Drawing.Point(216, 160);
this.button5.Name = "button5";
this.button5.Size = new System.Drawing.Size(112, 23);
this.button5.TabIndex = 5;
this.button5.Text = "button5";
this.button5.Click += new System.EventHandler(this.button5_Click);
//
// button6
//
this.button6.Location = new System.Drawing.Point(216, 192);
this.button6.Name = "button6";
this.button6.Size = new System.Drawing.Size(112, 23);
this.button6.TabIndex = 6;
this.button6.Text = "button6";
this.button6.Click += new System.EventHandler(this.button6_Click);
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(360, 273);
this.Controls.AddRange(new System.Windows.Forms.Control[] {
this.button6,
this.button5,
this.button4,
this.button3,
this.button2,
this.button1,
this.listbox1});
this.Name = "Form1";
this.Text = "Form1";
this.Load += new System.EventHandler(this.Form1_Load);
this.ResumeLayout(false);
}
#endregion
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.Run(new Form1());
}
private void button6_Click(object sender, System.EventArgs e)
{
//How to obtain list of files (example uses Windows folder).
this.listbox1.Items.Clear();
string[] files= Directory.GetFiles(winDir);
foreach (string i in files)
{
addListItem(i);
}
}
private void button1_Click(object sender, System.EventArgs e)
{
//How to read a text file.
//try...catch is to deal with a 0 byte file.
this.listbox1.Items.Clear();
StreamReader reader=new StreamReader(winDir + "\\system.ini");
try
{
do
{
addListItem(reader.ReadLine());
}
while(reader.Peek() != -1);
}
catch
{
addListItem("File is empty");}
finally
{
reader.Close();}
}
private void Form1_Load(object sender, System.EventArgs e)
{
this.button1.Text = "Read Text File";
this.button2.Text = "Write Text File";
this.button3.Text = "View File Information";
this.button4.Text = "List Drives";
this.button5.Text = "List Subfolders";
this.button6.Text = "List Files";
}
private void button5_Click(object sender, System.EventArgs e)
{
//How to get a list of folders (example uses Windows folder).
this.listbox1.Items.Clear();
string[] dirs = Directory.GetDirectories(winDir);
foreach(string dir in dirs)
{
addListItem(dir);
}
}
private void button4_Click(object sender, System.EventArgs e)
{
//Demonstrates how to obtain a list of disk drives.
this.listbox1.Items.Clear();
string[] drives = Directory.GetLogicalDrives();
foreach(string drive in drives)
{
addListItem(drive);
}
}
private void button3_Click(object sender, System.EventArgs e)
{
//How to retrieve file properties (example uses Notepad.exe).
this.listbox1.Items.Clear();
FileInfo FileProps =new FileInfo(winDir + "\\notepad.exe");
addListItem("File Name = " + FileProps.FullName);
addListItem("Creation Time = " + FileProps.CreationTime);
addListItem("Last Access Time = " + FileProps.LastAccessTime);
addListItem("Last Write TIme = " + FileProps.LastWriteTime);
addListItem("Size = " + FileProps.Length);
FileProps = null;
}
private void addListItem(string value)
{
this.listbox1.Items.Add(value);
}
private void button2_Click(object sender, System.EventArgs e)
{
//Demonstrates how to create and write to a text file.
StreamWriter writer = new StreamWriter("c:\\KBTest.txt");
writer.WriteLine("File created using StreamWriter class.");
writer.Close();
this.listbox1.Items.Clear();
addListItem("File Written to C:\\KBTest.txt");
}
}
}Note
You must change the code in Visual Studio 2005. By default, Visual C# adds one form to the project when you create a Windows Forms project. The form is named Form1. The two files that represent the form are named Form1.cs and Form1.designer.cs. You write the code in the Form1.cs file. The Windows Forms Designer writes the code in the Form1.designer.cs file.
For more information about the Windows Forms Designer in Visual C# 2005, visit the following Microsoft Developer Network (MSDN) Web site: - Press F5 to build and then run the program. Click the
buttons to view the different actions. When you view the sample code, you may
want to collapse the area named Windows Form Designer Generated Code to hide
this code.