How to Implement Flag Enums in C without External Libraries?

Customizing Flag Enums in C

In C , enumerations (enums) are powerful tools for representing discrete values. However, the standard enum syntax lacks a built-in mechanism for treating them as flags. This article explores how to implement flag-like enums in C without relying on external libraries.

Problem:

Consider the following example:

enum AnimalFlags {
    HasClaws = 1,
    CanFly = 2,
    EatsFish = 4,
    Endangered = 8
};

int seahawkFlags = CanFly | EatsFish | Endangered;

When you attempt to assign bitwise OR values to an enum, the compiler raises errors due to int/enum conversion mismatches.

Solution:

The solution lies in defining bitwise operators for the enum:

enum AnimalFlags {
    HasClaws = 1,
    CanFly = 2,
    EatsFish = 4,
    Endangered = 8
};

inline AnimalFlags operator|(AnimalFlags a, AnimalFlags b) {
    return static_cast<AnimalFlags>(static_cast<int>(a) | static_cast<int>(b));
}

// Define other operators as needed

int seahawkFlags = animalFlags::CanFly | AnimalFlags::EatsFish | AnimalFlags::Endangered;

By providing bitwise operators, the enum can be manipulated in a flag-like manner. Additionally, the use of type safety ensures that only valid flag combinations are assigned to the enum variable.

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