Книга: C# 2008 Programmer

Working with Files Using the File and FileInfo Classes

Working with Files Using the File and FileInfo Classes

The .NET Framework class library contains two similar classes for dealing with files — FileInfoand File.

The File class provides static methods for creating, deleting, and manipulating files, whereas the FileInfo class exposes instance members for files manipulation.

Like the Directory class, the File class only exposes static methods and does not contain any properties.

Consider the following program, which creates, deletes, copies, renames, and sets attributes in files, using the File class:

static void Main(string[] args) {
 string filePath = @"C:temptextfile.txt";
 string fileCopyPath = @"C:temptextfile_copy.txt";
 string newFileName = @"C:temptextfile_newcopy.txt";
 try {
  //---if file already existed---
  if (File.Exists(filePath)) {
   //---delete the file---
   File.Delete(filePath);
  }
  //---create the file again---
  FileStream fs = File.Create(filePath);
  fs.Close();
  //---make a copy of the file---
  File.Copy(filePath, fileCopyPath);
  //--rename the file---
  File.Move(fileCopyPath, newFileName);
  //---display the creation time---
  Console.WriteLine(File.GetCreationTime(newFileName));
  //---make the file read-only and hidden---
  File.SetAttributes(newFileName, FileAttributes.ReadOnly);
  File.SetAttributes(newFileName, FileAttributes.Hidden);
 } catch (IOException ex) {
  Console.WriteLine(ex.Message);
 } catch (Exception ex) {
  Console.WriteLine(ex.Message);
 }
 Console.ReadLine();
}

This program first checks to see if a file exists by using the Exists() method. If the file exists, the program deletes it using the Delete() method. It then proceeds to create the file by using the Create() method, which returns a FileStream object (more on this in subsequent sections). To make a copy of the file, you use the Copy() method. The Move() method moves a file from one location to another. Essentially, you can use the Move() method to rename a file. Finally, the program sets the ReadOnly and Hidden attribute to the newly copied file.

In addition to the File class, you have the FileInfo class that provides instance members for dealing with files. Once you have created an instance of the FileInfo class, you can use its members to obtain more information about a particular file. Figure 11-1 shows the different methods and properties exposed by an instance of the FileInfo class, such as the Attributes property, which retrieves the attributes of a file, the Delete() method that allows you to delete a file, and so on.


Figure 11-1

Reading and Writing to Files

The File class contains four methods to write content to a file:

WriteAllText() — Creates a file, writes a string to it, and closes the file

AppendAllText() — Appends a string to an existing file

WriteAllLines() — Creates a file, writes an array of string to it, and closes the file

WriteAllBytes() — Creates a file, writes an array of byte to it, and closes the file

The following statements show how to use the various methods to write some content to a file:

string filePath = @"C:temptextfile.txt";
string strTextToWrite = "This is a string";
string[] strLinesToWrite = new string[] { "Line1", "Line2" };
byte[] bytesToWrite =
 ASCIIEncoding.ASCII.GetBytes("This is a string");
File.WriteAllText(filePath, strTextToWrite);
File.AppendAllText(filePath, strTextToWrite);
File.WriteAllLines(filePath, strLinesToWrite);
File.WriteAllBytes(filePath, bytesToWrite);

The File class also contains three methods to read contents from a file:

ReadAllText() — Opens a file, reads all text in it into a string, and closes the file

ReadAllLines() — Opens a file, reads all the text in it into a string array, and closes the file

ReadAllBytes() — Opens a file, reads all the content in it into a byte array, and closes the file

The following statements show how to use the various methods to read contents from a file:

string filePath = @"C:temptextfile.txt";
string strTextToRead = (File.ReadAllText(filePath));
string[] strLinestoRead = File.ReadAllLines(filePath);
byte[] bytesToRead = File.ReadAllBytes(filePath);

The beauty of these methods is that you need not worry about opening and closing the file after reading or writing to it; they close the file automatically after they are done.

StreamReader and StreamWriter Classes

When dealing with text files, you may also want to use the StreamReader and StreamWriter classes. StreamReader is derived from the TextReader class, an abstract class that represents a reader that can read a sequential series of characters.

You'll see more about streams in the "The Stream Class" section later in this chapter.

The following code snippet uses the StreamReader class to read lines from a text file:

try {
 using (StreamReader sr = new StreamReader(filePath)) {
  string line;
  while ((line = sr.ReadLine()) != null) {
   Console.WriteLine(line);
  }
 }
} catch (Exception ex) {
 Console.WriteLine(ex.ToString());
}

In addition to the ReadLine() method, the StreamReader class supports the following methods:

Read() — Reads the next character from the input stream

ReadBlock() — Reads a maximum of specified characters

ReadToEnd() — Reads from the current position to the end of the stream

The StreamWriter class is derived from the abstract TextWriter class and is used for writing characters to a stream. The following code snippet uses the StreamWriter class to write lines to a text file:

try {
 using (StreamWriter sw = new StreamWriter(filePath)) {
  sw.Write("Hello, ");
  sw.WriteLine("World!");
 }
} catch (Exception ex) {
 Console.WriteLine(ex.ToString());
}

BinaryReader and BinaryWriter Classes

If you are dealing with binary files, you can use the BinaryReader and BinaryWriter classes. The following example reads binary data from one file and writes it into another, essentially making a copy of the file:

string filePath = @"C:tempVS2008Pro.png";
string filePathCopy = @"C:tempVS2008Pro_copy.png";
//---open files for reading and writing---
FileStream fs1 = File.OpenRead(filePath);
FileStream fs2 = File.OpenWrite(filePathCopy);
BinaryReader br = new BinaryReader(fs1);
BinaryWriter bw = new BinaryWriter(fs2);
//---read and write individual bytes---
for (int i = 0; i <= br.BaseStream.Length - 1; i++)
 bw.Write(br.ReadByte());
//---close the reader and writer---
br.Close();
bw.Close();

This program first uses the File class to open two files — one for reading and one for writing. The BinaryReader class is then used to read the binary data from the FileStream, and the BinaryWriter is used to write the binary data to the file.

The BinaryReader class contains many different read methods for reading different types of data — Read(), Read7BitEncodedInt(), ReadBoolean(), ReadByte(), ReadBytes(), ReadChar(), ReadChars(), ReadDecimal(), ReadDouble(), ReadInt16(), ReadInt32(), ReadInt64(), ReadSByte(), ReadSingle(), ReadString(), ReadUInt16(), ReadUInt32(), and ReadUInt64().

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