Chương 3-Bài 10. Xử lý Đọc/Ghi File trong C#

Workflow FileStream

Giải thích Buffer là gì?

Quá trình đọc file lấy luồng dữ liệu

A file is a collection of data stored in a disk with a specific name and a directory path. When a file is opened for reading or writing, it becomes a stream.

The stream is basically the sequence of bytes passing through the communication path. There are two main streams: the input stream and the output stream. The input stream is used for reading data from file (read operation) and the output stream is used for writing into the file (write operation).

C# I/O Classes

The System.IO namespace has various classes that are used for performing numerous operations with files, such as creating and deleting files, reading from or writing to a file, closing a file etc.

The following table shows some commonly used non-abstract classes in the System.IO namespace −

The FileStream Class

The FileStream class in the System.IO namespace helps in reading from, writing to and closing files. This class derives from the abstract class Stream.

You need to create a FileStream object to create a new file or open an existing file. The syntax for creating a FileStream object is as follows −

FileStream <object_name> = new FileStream( <file_name>, <FileMode Enumerator>,
   <FileAccess Enumerator>, <FileShare Enumerator>);

For example, we create a FileStream object F for reading a file named sample.txt as shown −

FileStream F = new FileStream("sample.txt", FileMode.Open, 
   FileAccess.Read, FileShare.Read);

Example

The following program demonstrates use of the FileStream class −

using System;
using System.IO;

namespace FileIOApplication {
   class Program {
      static void Main(string[] args) {
         FileStream F = new FileStream("test.dat", FileMode.OpenOrCreate, 
            FileAccess.ReadWrite);
         
         for (int i = 1; i <= 20; i++) {
            F.WriteByte((byte)i);
         }
         F.Position = 0;
         for (int i = 0; i <= 20; i++) {
            Console.Write(F.ReadByte() + " ");
         }
         F.Close();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 -1

Advanced File Operations in C#

The preceding example provides simple file operations in C#. However, to utilize the immense powers of C# System.IO classes, you need to know the commonly used properties and methods of these classes.

C# - Reading from and Writing to Text Files

The StreamReader and StreamWriter classes are used for reading from and writing data to text files. These classes inherit from the abstract base class Stream, which supports reading and writing bytes into a file stream.

The StreamReader Class

The StreamReader class also inherits from the abstract base class TextReader that represents a reader for reading series of characters. The following table describes some of the commonly used methods of the StreamReader class −

Example

The following example demonstrates reading a text file named Jamaica.txt. The file reads −

Down the way where the nights are gay
And the sun shines daily on the mountain top
I took a trip on a sailing ship
And when I reached Jamaica
I made a stop

using System;
using System.IO;

namespace FileApplication {
   class Program {
      static void Main(string[] args) {
         try {
            // Create an instance of StreamReader to read from a file.
            // The using statement also closes the StreamReader.
            using (StreamReader sr = new StreamReader("c:/jamaica.txt")) {
               string line;

               // Read and display lines from the file until 
               // the end of the file is reached. 
               while ((line = sr.ReadLine()) != null) {
                  Console.WriteLine(line);
               }
            }
         } catch (Exception e) {
            // Let the user know what went wrong.
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
         }
         Console.ReadKey();
      }
   }
}

Guess what it displays when you compile and run the program!

The StreamWriter Class

The StreamWriter class inherits from the abstract class TextWriter that represents a writer, which can write a series of character.

The following table describes the most commonly used methods of this class −

For a complete list of methods, please visit Microsoft's C# documentation.

Example

The following example demonstrates writing text data into a file using the StreamWriter class −

using System;
using System.IO;

namespace FileApplication {
   class Program {
      static void Main(string[] args) {
         string[] names = new string[] {"Zara Ali", "Nuha Ali"};
         
         using (StreamWriter sw = new StreamWriter("names.txt")) {

            foreach (string s in names) {
               sw.WriteLine(s);
            }
         }
         
         // Read and show each line from the file.
         string line = "";
         using (StreamReader sr = new StreamReader("names.txt")) {
            while ((line = sr.ReadLine()) != null) {
               Console.WriteLine(line);
            }
         }
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Zara Ali
Nuha Ali

Reading from and Writing into Binary files

The BinaryReader and BinaryWriter classes are used for reading from and writing to a binary file.

The BinaryReader Class

The BinaryReader class is used to read binary data from a file. A BinaryReader object is created by passing a FileStream object to its constructor.

The following table describes commonly used methods of the BinaryReaderclass.

The BinaryWriter Class

The BinaryWriter class is used to write binary data to a stream. A BinaryWriter object is created by passing a FileStream object to its constructor.

The following table describes commonly used methods of the BinaryWriter class.

For a complete list of methods, please visit Microsoft C# documentation.

Example

The following example demonstrates reading and writing binary data −

using System;
using System.IO;

namespace BinaryFileApplication {
   class Program {
      static void Main(string[] args) {
         BinaryWriter bw;
         BinaryReader br;
         
         int i = 25;
         double d = 3.14157;
         bool b = true;
         string s = "I am happy";
         
         //create the file
         try {
            bw = new BinaryWriter(new FileStream("mydata", FileMode.Create));
         } catch (IOException e) {
            Console.WriteLine(e.Message + "\n Cannot create file.");
            return;
         }
         
         //writing into the file
         try {
            bw.Write(i);
            bw.Write(d);
            bw.Write(b);
            bw.Write(s);
         } catch (IOException e) {
            Console.WriteLine(e.Message + "\n Cannot write to file.");
            return;
         }
         bw.Close();
         
         //reading from the file
         try {
            br = new BinaryReader(new FileStream("mydata", FileMode.Open));
         } catch (IOException e) {
            Console.WriteLine(e.Message + "\n Cannot open file.");
            return;
         }
         
         try {
            i = br.ReadInt32();
            Console.WriteLine("Integer data: {0}", i);
            d = br.ReadDouble();
            Console.WriteLine("Double data: {0}", d);
            b = br.ReadBoolean();
            Console.WriteLine("Boolean data: {0}", b);
            s = br.ReadString();
            Console.WriteLine("String data: {0}", s);
         } catch (IOException e) {
            Console.WriteLine(e.Message + "\n Cannot read from file.");
            return;
         }
         br.Close();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Integer data: 25
Double data: 3.14157
Boolean data: True
String data: I am happy

C# - Windows File System

C# allows you to work with the directories and files using various directory and file related classes such as the DirectoryInfo class and the FileInfoclass.

The DirectoryInfo Class

The DirectoryInfo class is derived from the FileSystemInfo class. It has various methods for creating, moving, and browsing through directories and subdirectories. This class cannot be inherited.

Following are some commonly used properties of the DirectoryInfo class −

Following are some commonly used methods of the DirectoryInfo class −

For a complete list of properties and methods, please visit Microsoft's C# documentation.

The FileInfo Class

The FileInfo class is derived from the FileSystemInfo class. It has properties and instance methods for creating, copying, deleting, moving, and opening of files, and helps in the creation of FileStream objects. This class cannot be inherited.

Following are some commonly used properties of the FileInfo class −

Following are some commonly used methods of the FileInfo class −

For complete list of properties and methods, please visit Microsoft's C# documentation.

Example

The following example demonstrates the use of the above-mentioned classes −

using System;
using System.IO;

namespace WindowsFileApplication {
   class Program {
      static void Main(string[] args) {
         //creating a DirectoryInfo object
         DirectoryInfo mydir = new DirectoryInfo(@"c:\Windows");
         
         // getting the files in the directory, their names and size
         FileInfo [] f = mydir.GetFiles();
         foreach (FileInfo file in f) {
            Console.WriteLine("File Name: {0} Size: {1}", file.Name, file.Length);
         }
         
         Console.ReadKey();
      }
   }
}

When you compile and run the program, it displays the names of files and their respective sizes in the Windows directory.