Working with Files in C#

Working with Files in C#(转)

In this article, you will learn how to manipulate directories and files in your system. Further, we will discuss how to read from and write to a file by using the powerful .NET classes.

The Namespace

System.IO provides all the necessary classes, methods, and properties for manipulating directories and files. Table 1 elaborates the main classes under this namespace.

Class	Purpose/Use
Binary Reader and Writer	Read and write primitive data types
Directory, File, DirectoryInfo, and FileInfo	Create, delete, and move files and directories. Get specific information about the files by making use of the properties defined in these classes.
FileStream	Access the files in a random fashion
MemoryStream	Access data stored in memory
StreamWriter and StreamReader	Read and write textual information
StringReader and StringWriter	Read and write textual Information from a string buffer

Table 1—Classes under System.IO

Working with DirectoryInfo and FileInfo classes

The base class of DirectoryInfo and FileInfo is FileSystemInfo. This is an abstract class, meaning you can't instantiate this class. But you can use the properties defined by this class. Table 2 elaborates its properties and methods.

Properties	Purpose/Use
Attributes	Returns attributes associated with a file. Takes FileAttributes enumeration values
CreationTime	Returns the time of creation of the file
Exists	Checks whether a supplied file is a directory or not
Extension	Returns the file extension
LastAccessTime	Returns last accessed time of the file
FullName	Returns the full path of the file
LastWriteTime	Returns the time of last written activity to the file
Name	Returns the name of a given file
Delete()	Deletes a file. Be careful when using this method.

Table 2—Members of FileSystemInfo class

The DirectoryInfo class provides methods for creating, moving, and deleting directories. To make use of the above properties, create an object of the DirectoryInfo class as shown in Listing 1:

Listing 1

DirectoryInfo dir1 = new DirectoryInfo(@"F:\WINNT");

You then can access the properties by using the object dir1, as shown in the code fragment in Listing 2:

Listing 2

Console.WriteLine("Full Name is : {0}", dir1.FullName);
Console.WriteLine("Attributes are : {0}",
                   dir1.Attributes.ToString());

You can also apply the values of FileAttributes enumeration. Its values are shown in Table 3.

Properties	Purpose/Use
Archive	Returns the file's Archive status
Compressed	Returns whether the file is compressed or not
Directory	Returns whether the file is a directory or not
Encrypted	Returns whether the file is encrypted or not
Hidden	Returns whether the file is hidden or not
Offline	Signifies that the data is not available
ReadOnly	Indicates that the file is read only
System	Indicates that the file is a System file (probably a file under the Windows folder)

Table 3—FileAttributes Enumeration Values

Working with Files under a Directory

Suppose that you want to list all BMP files under the f:\Pictures directory. You can write a code as shown in the code snippet given in Listing 3:

Listing 3

DirectoryInfo dir = new DirectoryInfo(@"F:\WINNT");
FileInfo[] bmpfiles = dir.GetFiles("*.bmp);
Console.WriteLine("Total number of bmp files", bmpfiles.Length);
Foreach( FileInfo f in bmpfiles)
{
  Console.WriteLine("Name is : {0}", f.Name);
  Console.WriteLine("Length of the file is : {0}", f.Length);
  Console.WriteLine("Creation time is : {0}", f.CreationTime);
  Console.WriteLine("Attributes of the file are : {0}",
                     f.Attributes.ToString());
}

Creating Subdirectories

You can easily create a subdirectory. Listing fragment 4 describes how to create a subdirectory called MySub under the Sub directory.

Listing 4

DirectoryInfo dir = new DirectoryInfo(@"F:\WINNT");
try
{
  dir.CreateSubdirectory("Sub");
  dir.CreateSubdirectory(@"Sub\MySub");
}
catch(IOException e)
{
  Console.WriteLine(e.Message);
}

Creating Files by Using the FileInfo Class

With the FileInfo class, you can create new files, access information about the files, delete, and move files. This class also provides methods for opening, reading from, and writing to a file. Listing 5 shows how to create a text file and access its information like its creation time, full name, and so forth.

Listing 5

FileInfo fi = new FileInfo(@"F:\Myprogram.txt");
FileStream fstr = fi.Create();
Console.WriteLine("Creation Time: {0}",f.CreationTime);
Console.WriteLine("Full Name: {0}",f.FullName);
Console.WriteLine("FileAttributes: {0}",f.Attributes.ToString());

//Way to delete Myprogram.txt file.

Console.WriteLine("Press any key to delete the file");
Console.Read();
fstr.Close();
fi.Delete();

Understanding the Open() Method

The FileInfo class defines a method named Open() with which you can create files by applying the values of the FileMode and FileAccess enumerations. The code snippet in Listing 6 describes its usage:

Listing 6

FileInfo f = new FileInfo("c:\myfile.txt");
FileStream s = f.Open(FileMode.OpenorWrite, FileAccess.Read);

You then can read from and write to a file by using the object 's'. In the overloaded Open() method, permission is given only for reading from a file. If you want to write to a file, you have to apply the ReadWrite value of FileAccess enumeration. Tables 4 and 5 describe the values of the FileMode and FileAccess enumerations.

Values	Purpose/Use
Append	Opens the file and adds data. This should be used with the FileAccess Write Enumeration value.
Create	Creates a new file. Overwrites any existing file.
CreateNew	Creates a new file. If the file already exists, IOException is thrown.
Open	Opens an existing file
OpenOrCreate	Opens a new file. If there is no file, it creates a new file.
Truncate	Truncates an existing file

Table 4—FileMode Enumeration values

Values	Purpose/Use
Read	Data can be read (retrieved) from the file
ReadWrite	Data can be added to and retrieved from the file
Write	Data can be added to the file

Table 5—FileAccess Enumeration values

Writing to a Text File by Using the StreamWriter Class

You can easily write texts or other information to a file by using the CreateText() method of the FileInfo class. However, you have to obtain a valid StreamWriter. It's this StreamWriter reference that provides the required functionalities for writing to a file. To illustrate, Listing 7 writes a series of texts to the Mytext.txt file.

Listing 7

FileInfo f = new FileInfo("Mytext.txt")
StreamWriter w = f.CreateText();
w.WriteLine("This is from");
w.WriteLine("Chapter 6");
w.WriteLine("Of C# Module");
w.Write(w.NewLine);
w.WriteLine("Thanks for your time");
w.Close();

Reading from a Text File

You can read from a Text file by using the StreamReader class. For this, you have to specify the file name using the static OpenText() method of the File class. Listing 8 reads the contents that we have written in Listing 7:

Listing 8

Console.WriteLine("Reading the contents from the file");
StreamReader s = File.OpenText("Mytext.txt");
string read = null;
while ((read = s.ReadLine()) != null)
{
  Console.WriteLine(read);
}
s.Close();

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About the Author

Anand Narayanaswamy works as a freelance Web/Software developer and technical writer. He runs and maintains learnxpress.com, and provides free technical support to users. His areas of interest include Web development, Software development using Visual Basic, and in the design and preparation of courseware, technical articles, and tutorials.

Working with Files in C#