Constexpr Functions vs. Constants: When Should You Choose One Over the Other?

Utility of Constexpr Functions vs. Constants

Despite the seemingly straightforward purpose of a function to execute code, C 11 introduces the concept of constexpr functions, which are functions that return constant values. This raises the question: when should one declare a constant instead of writing a constexpr function?

Benefits of Constexpr Functions

While it may seem logical to define a constant for simple value returns, constexpr functions offer several advantages:

• Complex Calculations: Functions can handle more complex calculations that constants cannot, such as operations involving multiple parameters.
• Readability: Functions provide better readability for code that performs more complex processing.
• Compile-Time Evaluation: Functions allow for compile-time evaluation of constant values, optimizing performance by avoiding runtime calculations.

Examples of Useful Cases

For example, consider the MeaningOfLife function:

constexpr int MeaningOfLife ( int a, int b ) { return a * b; }

Here, MeaningOfLife can be evaluated at compile time, even though it involves multiplication. Similarly, a DegreesToRadians function provides a convenient way to convert degrees to radians:

const float oneeighty = DegreesToRadians( 180.0f );

Comparison to Constants

Constants are useful for simple values that do not require computation. However, when dealing with more complex calculations, compile-time evaluations, or improved readability, constexpr functions offer a clear advantage.

Therefore, by understanding the capabilities and benefits of constexpr functions, developers can make informed decisions about when to declare constants or write constexpr functions in their code.

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