Recipe 11.1 Creating, Copying, Moving, and Deleting a File

Problem

You need to create a new file, copy an existing file, move an existing file, or delete a file.

Solution

The System.IO namespace contains two classes to perform these actions: the File and FileInfo classes. The File class contains only static methods, while the FileInfo class contains only instance methods.

File 's static Create method returns an instance of the FileStream class, which you can use to read from or write to the newly created file. For example, the following code uses the static Create method of the File class to create a new file:

FileStream fileStream = null;
if (!File.Exists(@"c:\delete\test\test.txt"))
{
    fileStream = File.Create(@"c:\delete\test\test.txt");
}

The Create instance method of the FileInfo class takes no parameters. You should supply the path with a filename as the only parameter to the FileInfo class constructor. The method returns an instance of the FileStream class that you can use to read from or write to the newly created file. For example, the following code uses the Create instance method of the FileInfo class to create a new file:

FileInfo fileInfo = null;
FileStream fileStream = null;
if (!File.Exists (@"c:\delete\test\test.txt"))
{
    fileInfo = new FileInfo(@"c:\delete\test\test.txt");
    fileStream = fileInfo.Create( );
}

You can copy a file using the overloaded static File.Copy method that returns void. The third parameter of one of the overrides for this function allows you to pass true or false depending upon whether you want to overwrite an existing destination file, as shown in the following code, which uses the static Copy method of the File class to copy a file:

if (File.Exists(@"c:\delete\test\test.txt"))
{
    File.Copy(@"c:\delete\test\test.txt ", 
               Directory.GetCurrentDirectory( ) + @"\test.txt", true);
}

The overloaded CopyTo instance method returns a FileInfo object that represents the newly copied file. This method can also take a Boolean in one of the overrides to signify your intent to overwrite an existing file. For example, the following code uses the CopyTo instance method of the FileInfo class to copy a file:

FileInfo fileInfo = new FileInfo(@"c:\delete\test\test.txt");
fileInfo.CopyTo(@"c:\test.txt", true);

You can move a file using the static Move method of the File class, which returns void. For example, the following code uses the static Move method to move a file after checking for its existence:

if (!File.Exists(Directory.GetCurrentDirectory( ) + @"\test.txt"))
{
    File.Move(@"c:\delete\test\test.txt ", 
         Directory.GetCurrentDirectory( ) + @"\test.txt");
}

The MoveTo instance method returns void and is the way to move a file using the FileInfo class. For example, the following code moves a file using the MoveTo instance method of the FileInfo class after checking for the file's existence:

FileInfo fileInfo = new FileInfo(@"c:\delete\test\test.txt");
if (!File.Exists(@"c:\test.txt "))
{
    fileInfo.MoveTo(@"c:\test.txt ");
}

You can delete a file using the static Delete method of the File class that returns void. For example, the following code uses the static Delete method to delete a file:

if (File.Exists(Directory.GetCurrentDirectory( ) + @"\test.txt"))
{
    File.Delete(Directory.GetCurrentDirectory( ) + @"\test.txt", true);
}

The Delete instance method on the FileInfo class takes no parameters and returns void. For example, the following code uses the Delete instance method of the FileInfo class to delete a file:

if(File.Exists(@"c:\delete\test\test.txt")
{
    FileInfo fileInfo = new FileInfo(@"c:\delete\test\test.txt");
    fileInfo.Delete( );
}

Discussion

Whether you choose to call the static file operation methods or the instance file operation methods depends on what you are trying to accomplish. If you need a quick way of creating, moving, copying, or deleting a file, consider using the static methods. If you will be performing multiple operations on a file, such as creating, moving, and changing its attributes, you should consider the instance methods of the FileInfo class. Another consideration is that static methods on a class do not require an object to be created on the managed heap and subsequently destroyed by the garbage collector. Instance methods require an object to be created before the methods can be called. If you are trying to minimize the number of objects the garbage collector has to manage, consider using static methods.

A few items to note when using the file functions:

• If the directory doesn't exist, the method won't create it and you'll get an exception. See how to check whether a directory exists in Recipe 11.4.

• If no path is provided, the file will land in the current working directory. If the user does not have permission to write to the current working directory (such as the case of a normal user writing to the Program Files directory), this will result in an UnauthorizedAccessException.

• If a relative path is provided (for example, C:\dir1\dir2\..\..\file.txt), it will be evaluated properly.

• If an absolute path is provided, the method will succeed as expected.

When creating a new file, you should first determine whether that file already exists. This is a good idea since the default creation behavior of the file classes is to either overwrite the existing file silently or, if the file is read-only, to throw an exception. The File and FileInfo classes both contain a method, Exists, to perform this operation. Once it is determined that the file does not exist, we can create it using either the static or instance Create methods. Note that this does leave a small window open between the time you checked and the time that the creation starts, so it is not a replacement for proper exception and error handling of the Create call.

See Also

See the "File Class" and "FileInfo Class" topics in the MSDN documentation.