Exception Handling

Syntax

try {\n  // risky code\n} catch (ExceptionType e) {\n  // handle it\n} finally {\n  // always runs\n}

Examples

try
{
    int result = 10 / int.Parse("0");
}
catch (DivideByZeroException e)
{
    Console.WriteLine($"Error: {e.Message}");
}

Console.WriteLine("Program continues running");

void Process(string input)
{
    try
    {
        int number = int.Parse(input);
        int result = 100 / number;
        Console.WriteLine(result);
    }
    catch (FormatException)
    {
        Console.WriteLine($"Not a valid number: {input}");
    }
    catch (DivideByZeroException)
    {
        Console.WriteLine("Cannot divide by zero");
    }
}

Process("abc");  // Not a valid number: abc
Process("0");     // Cannot divide by zero
Process("5");     // 20

void ReadFile()
{
    Console.WriteLine("Opening file...");
    try
    {
        throw new InvalidOperationException("File not found");
    }
    catch (InvalidOperationException e)
    {
        Console.WriteLine($"Error: {e.Message}");
    }
    finally
    {
        Console.WriteLine("Closing file...");  // always runs
    }
}

ReadFile();

public class InsufficientFundsException : Exception
{
    public InsufficientFundsException(string message) : base(message) { }
}

public class BankAccount
{
    private double _balance;
    public BankAccount(double balance) => _balance = balance;

    public void Withdraw(double amount)
    {
        if (amount > _balance)
            throw new InsufficientFundsException("Not enough funds for this withdrawal");
        _balance -= amount;
    }
}

BankAccount account = new BankAccount(100);
try
{
    account.Withdraw(200);
}
catch (InsufficientFundsException e)
{
    Console.WriteLine($"Transaction failed: {e.Message}");
}

Best practices

• Catch specific exception types rather than a broad catch (Exception e), so unrelated bugs are not accidentally silenced
• Use finally (or better, a using statement/declaration) for cleanup code that absolutely must run, like closing files or database connections
• Create custom exception classes, deriving from Exception, for domain-specific errors that callers should be able to catch distinctly
• Don't use exceptions for routine control flow when a simple if check (or TryParse-style pattern) would do - they carry real performance overhead

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation