Working with Files in C#
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.IOWorking with DirectoryInfo and FileInfo classesThe 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 classThe 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 1DirectoryInfo 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 ValuesWorking with Files under a DirectorySuppose 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 SubdirectoriesYou can easily create a subdirectory. Listing
fragment 4 describes how to create a subdirectory called MySub under
the Sub directory.
Listing 4DirectoryInfo 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 ClassWith 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 5FileInfo 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() MethodThe 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 6FileInfo 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 valuesValues | 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 valuesWriting to a Text File by Using the StreamWriter ClassYou 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 7FileInfo 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 FileYou 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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