How to cast int to enum in C#?

To cast an integer to an enum in C#, you can use direct casting or helper methods like Enum.IsDefined for validation. Here’s a detailed guide:

1. Direct Casting

Use explicit casting if you’re certain the integer corresponds to a valid enum value:

public enum Status { Pending = 0, Active = 1, Inactive = 2 }

int value = 1;
Status status = (Status)value; // Status.Active

2. Validate the Integer First

Use Enum.IsDefined to check if the integer maps to a defined enum value:

int value = 3;
if (Enum.IsDefined(typeof(Status), value)) {
    Status status = (Status)value;
} else {
    // Handle invalid value (e.g., throw an error or assign a default)
    throw new ArgumentException($"Invalid value: {value}");
}

3. For Non-int Underlying Types

If the enum uses a non-int underlying type (e.g., byte), use Enum.ToObject:

public enum Priority : byte { Low = 1, Medium = 2, High = 3 }

int value = 2;
Priority priority = (Priority)Enum.ToObject(typeof(Priority), value); // Priority.Medium

4. Handling Undefined Values

Casting works even for undefined values, but the result won’t match a named enum member:

int value = 99;
Status status = (Status)value; // Valid, but no named enum member corresponds to 99
Console.WriteLine(status); // Output: 99

Key Notes

• Default Underlying Type: Enums default to int, but you can specify others (e.g., byte, long).
• Validation: Always validate untrusted input (e.g., user input) with Enum.IsDefined.
• Flags Enums: For [Flags] enums, integers can represent bitwise combinations of values.

Example Workflow

using System;

public enum Color { Red = 1, Green = 2, Blue = 3 }

public class Program {
    public static void Main() {
        int input = 2;

        if (Enum.IsDefined(typeof(Color), input)) {
            Color color = (Color)input;
            Console.WriteLine($"Color: {color}"); // Output: Green
        } else {
            Console.WriteLine("Invalid color value.");
        }
    }
}

When to Use Which

Method	Use Case
Direct Cast	Trusted values (e.g., hardcoded integers).
Enum.IsDefined	Validate untrusted input (e.g., user data).
Enum.ToObject	Non-int underlying types (e.g., byte).

By following these methods, you can safely convert integers to enums in C#!