Introduction

It is important to understand what happens when we cast numeric values in .NET, the result might not be what you are expecting. Here, I am showing how to use OverflowException to prevent unexpected behaviors.

The Default Behavior

When writing code in C#, if we cast a numeric value to another type that doesn't not have enough bits to represent it, the compiler will truncate the number to the maximum value supported.

For example:

using System;

class Program
{
  static void Main(string[] args)
  {
    long longValue = long.MaxValue;
    Console.WriteLine((byte)longValue);
  }
}

// Output: 255

Validate using OverFlowExceptions

In order to ensure that the cast will not silently change the value, we need to wrap the code into a check block.

using System;

class Program
{
  static void Main(string[] args)
  {
    long longValue = long.MaxValue;
    try
    {
      checked
      {
        Console.WriteLine((byte)longValue);
      }
    }
    catch (OverflowException)
    {
      Console.WriteLine($"Unable to cast {longValue} to byte.");
    }
  }
}

// Output: Unable to cast 9223372036854775807 to byte.

Wrapping the code inside a check block will ensure that it will throw an exception if the value is too big for the target type. For more information, check out the official documentation.