Exceptions in C#

An exception in C# is an object that represents an error that occurs during the execution of a program. When an exception occurs, the normal flow of the program is interrupted. Then a block called try-catch is searched for to capture (and handle) the error.

If there is no try-catch block to capture the exception, it goes “upward.” If no one handles it, the exception will reach the main function (the normal outcome is that the program terminates abruptly).

Throwing an exception

In C#, we can throw an exception ourselves using the throw keyword. By throwing an exception, we are indicating that an error has occurred and we want to notify the program.

throw new Exception("An error occurred");

Predefined exceptions

In C#, there are different types of exceptions that we can catch using the try-catch block. Some examples of common exceptions are:

string name = null;
int length = name.Length;  // Will throw NullReferenceException

int[] numbers = {1, 2, 3};
int value = numbers[5];  // Will throw IndexOutOfRangeException

int divisor = 0;
int result = 10 / divisor;  // Will throw DivideByZeroException

using (StreamReader reader = new StreamReader("non_existent_file.txt"))
{
    string content = reader.ReadToEnd();  // Will throw FileNotFoundException
}

void SetAge(int age)
{
    if (age < 0) throw new ArgumentException("Age cannot be negative.");
}
SetAge(-5);  // Will throw ArgumentException

List<int> list = new List<int>();
int value = list[0];  // Will throw InvalidOperationException if the list is empty

string number = "abc";
int value = int.Parse(number);  // Will throw FormatException

using (StreamWriter writer = new StreamWriter("file.txt"))
{
    writer.WriteLine("Hello World");  // Will throw IOException if there is a problem with the file
}

:::::::

TimeoutException: Occurs when an operation exceeds the allowed timeout. For example, in network or database operations:

// Simplified example
var client = new HttpClient();
client.Timeout = TimeSpan.FromSeconds(1);  // Short timeout for the example
var response = await client.GetAsync("https://www.example.com");  // Will throw TimeoutException if the timeout is exceeded

Creating your own exceptions in .NET

In addition to using predefined exceptions in .NET, it is possible to create our own custom exceptions. This allows us to be more specific when handling errors in your applications.

To create our own exceptions, we simply need to create a class that inherits from the base class Exception (then you can add any property or method you need to provide additional information about the error).

Here is an example of a custom exception class:

public class MyException : Exception
{
    public MyException(string message) : base(message) { }
    public MyException(string message, Exception innerException) : base(message, innerException) { }
}

Once you have your custom exception class, you can use it in your code just like you would use any other .NET exception. For example:

try
{
    // Code that may throw an exception
    throw new MyException("Error in my application");
}
catch (MyException ex)
{
    // Handling the custom exception
}