Week 5 - Streams

Do the Practical

In this topic, we will learn about streams in C#. A stream is a sequence of bytes that can be read from or written to. Streams are used to read and write data from and to files, network connections, and other sources in a sequential manner.

Directory and File I/O

Documenting the File System

The System.IO namespace contains classes that allow you to work with files and directories.

Checking for the Existence of a File or Directory

The File and Directory classes contain methods that allow you to check whether a file or directory exists.

For example, the following code checks whether the C:\Users\Public\Documents directory exists, then checks whether the C:\Users\Public\Documents\MyFile.txt file exists.

if (Directory.Exists("C:\Users\Public\Documents"))
{
    // Directory exists
    if (File.Exists("C:\Users\Public\Documents\MyFile.txt"))
    {
        // File exists
    }
    else
    {
        // File does not exist
    }
}
else
{
    // Directory does not exist
}

Information About a File or Directory

The Directory and File classes contain methods that allow you to get information about a file or directory.

For example, the following code gets the creation date and time of the C:\Users\Public\Documents directory, then gets the creation date and time of the C:\Users\Public\Documents\MyFile.txt file.

Console.WriteLine(Directory.GetCreationTime("C:\Users\Public\Documents"));
Console.WriteLine(File.GetCreationTime("C:\Users\Public\Documents\MyFile.txt"));

Listing Files and Directories

The Directory class contain methods that allow you to list files and directories.

For example, the following code lists all the files in the C:\Users\Public\Documents directory, then lists all the subdirectories in the C:\Users\Public\Documents directory.

foreach (string file in Directory.GetFiles("C:\Users\Public\Documents"))
{
    Console.WriteLine(file);
}

foreach (string directory in Directory.GetDirectories("C:\Users\Public\Documents"))
{
    Console.WriteLine(directory);
}

File Reading

To read from a file, you can use a StreamReader object.

The following code creates a StreamReader object to read from the C:\Users\Public\Documents\MyFile.txt, then displays each line of the file.

using (StreamReader reader = new StreamReader("C:\Users\Public\Documents\MyFile.txt"))
{
    string line;
    while ((line = reader.ReadLine()) != null)
    {
        Console.WriteLine(line);
    }
}

Alternatively, use !readline.EndOfStream to read through the file.

string path = "C:\Users\Public\Documents\MyFile.txt";
using (StreamReader reader = new StreamReader(path))
{
    string line = null;
    // Read through the whole file
    do
    {
        line = reader.ReadLine();
        Console.WriteLine(line);
    } while (!reader.EndOfStream);
}

Note that the using statement is used to ensure that the StreamReader object is disposed of correctly. If you do not use the using statement, you must call the StreamReader.Close() method to dispose of the object.

File Writing

To write to a file, you can use a StreamWriter object.

The following code creates a StreamWriter object to write to the C:\Users\Public\Documents\MyFile.txt, then writes the text “Hello World!” to the file. This will overwrite all the current content in the file.

string path = "C:\Users\Public\Documents\MyFile.txt";
using (StreamWriter writer = new StreamWriter(path))
{
    writer.WriteLine("Hello World!");
}

To append to the file instead, set the append parameter in the StreamWriter’s constructor to true:

using (StreamWriter writer = new StreamWriter(path, append: true))
{
    writer.WriteLine("Hello World!");
}

Command Line Arguments

The Main method of a C# program can accept command line arguments. These arguments are passed to the program as an array of strings.

For example, the following code displays the command line arguments passed to the program.

static void Main(string[] args)
{
    foreach (string arg in args)
    {
        Console.WriteLine(arg);
    }
}

In Visual Studio, you can pass command line arguments to a program by right-clicking the project in the Solution Explorer, then selecting Properties. In the Debug tab, enter the command line arguments in the Command line arguments box.