Difference: enum and enum class in C++

Explanation of enum and enum class in C++ with Examples

1. enum (Traditional Enumeration)

enum is a user-defined type that allows assigning names to integral constants, making the code more readable. Traditional enum types are implicitly converted to integers, which can sometimes lead to unexpected behavior.

Example of enum

#include <iostream>

enum Color {
    RED,    // Implicitly assigned 0
    GREEN,  // Implicitly assigned 1
    BLUE    // Implicitly assigned 2
};

int main() {
    Color myColor = GREEN;  // Assigning the enum value

    if (myColor == 1) { // This works because `GREEN` is implicitly 1
        std::cout << "Color is GREEN." << std::endl;
    }

    return 0;
}

Explanation:

• The enum Color defines three named constants: RED, GREEN, and BLUE.
• These constants are automatically assigned integer values starting from 0.
• The implicit conversion allows you to compare myColor with an integer, which can be a downside as it may lead to bugs when used incorrectly.

Issues with enum:

• It allows implicit conversion to integers, which can lead to type safety issues.
• Different enums can have overlapping values, leading to potential conflicts.

2. enum class (Scoped Enumeration)

enum class (also called “strongly typed enumerations”) was introduced in C++11 to address some of the issues with traditional enums. It provides better type safety and scope management.

Example of enum class

#include <iostream>

enum class Color {
    RED,    // Implicitly assigned 0
    GREEN,  // Implicitly assigned 1
    BLUE    // Implicitly assigned 2
};

int main() {
    Color myColor = Color::GREEN;  // Using scoped enumeration

    // if (myColor == 1) { } // This will cause a compilation error

    if (myColor == Color::GREEN) {
        std::cout << "Color is GREEN." << std::endl;
    }

    return 0;
}

Explanation:

• enum class defines a scoped enumeration where the enumerators (RED, GREEN, BLUE) are scoped under the enumeration name (Color).
• This means you need to use Color::GREEN to access the value.
• Implicit conversion to integers is not allowed, so comparisons like myColor == 1 will cause a compilation error, enhancing type safety.

Benefits of enum class:

• Strong typing: enum class values do not implicitly convert to integers.
• Scoped: The names of the enumeration values are scoped within the enumeration, reducing the chance of naming conflicts.

Summary

Feature	enum	enum class
Implicit Conversion	Yes	No
Scoped Names	No	Yes
Type Safety	Low	High
Usage Syntax	RED	Color::RED

Using enum class is generally preferred in modern C++ as it offers better type safety and avoids the pitfalls of traditional enumerations.