Working with Files

There's a parallel set of classes to Directory and DirectoryInfo that enables you to work with files File and FileInfo . The File class works with files in general, and the FileInfo class works with a specific file. Like Directory , File is a static class, and you can see the significant public methods of this class in Table 5.4, which let you create files, delete them, move them, and more.

Table 5.4. Significant Static Public File Methods

METHOD	PURPOSE
AppendText	Appends Unicode text to a file.
Copy	Copies a file to a new file.
Create	Creates a file using the given path .
CreateText	Creates or opens a file for writing.
Delete	Deletes the given file. (No exception is thrown if the given file does not exist.)
Exists	Determines whether the given file exists.
GetCreationTime	Returns the creation date and time of the given file or directory.
GetLastAccessTime	Returns the date and time the given file or directory was last accessed.
GetLastWriteTime	Returns the date and time the given file or directory was written to last.
Move	Moves a given file to a new location.
Open	Opens a file stream for a file.
OpenRead	Opens an existing file for reading.
OpenText	Opens an existing text file for reading.
OpenWrite	Opens an existing file for writing.
SetCreationTime	Sets the date and time the file was created.
SetLastAccessTime	Sets the date and time the given file was last accessed.
SetLastWriteTime	Sets the date and time that the given file was last written to.

You can see the significant public properties of the FileInfo class in Table 5.5 and its significant public methods in Table 5.6.

Table 5.5. Significant Public FileInfo Properties

PROPERTY	PURPOSE
CreationTime	Returns or sets the creation time of the current FileSystemInfo object.
Exists	Returns true if a file exists, false otherwise .
Extension	Returns the string representing the extension part of the file.
FullName	Returns the full path of the directory or file.
LastAccessTime	Returns or sets the time the current file or directory was last accessed.
LastWriteTime	Returns or sets the time when the current file or directory was written to last.
Length	Returns the size of a file.
Name	Returns the name of the file.

Table 5.6. Significant Public FileInfo Methods

METHOD	PURPOSE
AppendText	Appends text to the file.
CopyTo	Copies an existing file to a new one.
Create	Creates a file.
CreateText	Creates a StreamWriter object that writes a new text file.
Delete	Deletes a file.
MoveTo	Moves a given file to a new location.
Open	Opens a file.
OpenRead	Creates a read-only FileStream object.
OpenText	Creates a StreamReader that reads from an existing text file.
OpenWrite	Creates a write-only FileStream object.
Refresh	Refreshes the state of the object.

Here's an example using the FileInfo class to determine the name, length, and last modified date of all the files in the current directory. You can use the GetFiles method of a DirectoryInfo object to get an array of FileInfo objects. We loop over that array in ch05_02.cs, Listing 5.2, displaying the filenames and last-modified times.

Listing 5.2 Getting File Information (ch05_02.cs)

 using System.IO; class ch05_02 {   public static void Main()   {     string currentDirectory =       System.Environment.CurrentDirectory;     DirectoryInfo dir = new DirectoryInfo(currentDirectory);     FileInfo[] files = dir.GetFiles();  foreach (FileInfo file in files)   {   System.Console.WriteLine(   "{0} is {1} bytes long, last modified {2}.",   file.Name, file.Length, file.LastWriteTime);   }  } } 

Here's the kind of display you see when you run ch05_02.cs:

 C:\>ch05_02 ch05_02.cs is 518 bytes long, last modified 2/17 2:00:04 PM. ch05_02.exe is 3584 bytes long, last modified 2/17 2:00:06 PM. 

Here's another example, using the DirectoryInfo method CreateSubdirectory to create a new subdirectory named backup , and the FileInfo CopyTo method to copy all files in the current directory to the backup directory. You can see how this code works in ch05_03.cs, Listing 5.3.

Listing 5.3 Copying Files (ch05_03.cs)

 using System.IO; class ch05_03 {   public static void Main()   {     string currentDirectory =       System.Environment.CurrentDirectory;     DirectoryInfo dir = new DirectoryInfo(currentDirectory);  DirectoryInfo backupDirectory =   dir.CreateSubdirectory("backup");   FileInfo[] files = dir.GetFiles();   foreach (FileInfo file in files)   {   string newName = backupDirectory.FullName +   @"\" + file.Name;   file.CopyTo(newName);   }  } } 

As you can see, the Directory , DirectoryInfo , File , and FileInfo classes enable you to work with directories and files without actually handing the data inside a file. As such, they provide only external services when handling your data; to open files and access their contents directly, you use streams.