Checking for Constant Expressions in C: A Macro Approach

This article explores various methods for creating a C macro that detects if an expression is a constant expression. The author investigates several techniques, including C23's static compound literals, GNU extension `__builtin_constant_p`, `static_assert`, `sizeof` combined with compound literal arrays, `sizeof` with enum constants, and the comma operator. Each method has its pros and cons; C23 support is limited, `__builtin_constant_p` relies on GNU extensions, `static_assert` and `sizeof` methods might alter the expression's type, and the comma operator generates warnings. The author concludes that a perfect solution is elusive, and the best choice depends on specific needs and the C standard version.