`const` vs. `constexpr` in C : When Should You Use Which?

const vs constexpr: A Comprehensive Comparison

Variables declared with the keywords const and constexpr both represent constants in C . However, there exist significant differences between the two that necessitate careful consideration when selecting the appropriate keyword for specific situations.

Compile-Time vs Run-Time Initialization

const variables can be initialized either at compile-time or run-time, while constexpr variables must be initialized at compile-time. This distinction is crucial since compile-time initialization ensures that the value is known before the program executes.

Usage in Contexts Requiring Compile-Time Constants

constexpr variables, but not const variables, can be used in contexts that demand compile-time constants. For example, constexpr variables can be used to define constexpr functions and template parameters, where compile-time values are required.

Error Reporting

Errors related to incorrect usage of const or constexpr are handled differently by the compiler. Errors involving constexpr variables are reported during compilation, while errors involving const variables may not be detected until run-time. This allows constexpr variables to identify potential issues early on, improving code quality and reliability.

Which Style Should Be Preferred?

The choice between const and constexpr depends on specific requirements. If initialization at compile-time is essential and the value must be utilized in compile-time contexts, constexpr should be employed. However, if run-time initialization is necessary, const remains the appropriate choice.

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