Custom exceptions

Context: Custom exceptions allow you to define application-specific error types. They should inherit from Exception (or a derived class) and follow standard conventions: provide constructors that call the base constructors, implement serialization for cross‑domain scenarios, and add custom properties when needed. Custom exceptions make error handling more expressive and maintainable.

Usage Example

using System;

public class InsufficientFundsException : Exception
{
    public decimal Amount { get; }
    public decimal Balance { get; }

    public InsufficientFundsException() { }

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

    public InsufficientFundsException(string message, Exception inner) : base(message, inner) { }

    public InsufficientFundsException(decimal amount, decimal balance)
        : base($"Insufficient funds: requested {amount:C}, balance {balance:C}")
    {
        Amount = amount;
        Balance = balance;
    }
}

class BankAccount
{
    public decimal Balance { get; private set; }

    public void Withdraw(decimal amount)
    {
        if (amount > Balance)
            throw new InsufficientFundsException(amount, Balance);
        Balance -= amount;
    }
}

class Program
{
    static void Main()
    {
        var account = new BankAccount();
        try
        {
            account.Withdraw(100);
        }
        catch (InsufficientFundsException ex)
        {
            Console.WriteLine(ex.Message);
        }
    }
}

Output console

dotnet run
Insufficient funds: requested $100.00, balance $0.00

Important notes

Avoid inheriting from ApplicationException (it is no longer recommended).
Provide at least the three standard constructors.
Mark the exception as [Serializable] if you need cross‑AppDomain or cross‑process support.

Real-world usage example

Validation framework – Create ValidationException with a collection of validation errors.
See .NET docs on creating custom exceptions.

Custom exceptions

Usage Example

Output console

Important notes

Real-world usage example

Related sections