Does constexpr Imply Inline in C ?

Inline Implication of Constexpr: An Analysis

In the realm of C syntax, the constexpr and inline specifiers play significant roles in function declarations. The question arises: whether the constexpr specifier carries the same implications as the inline specifier?

Inline Specifier

The inline specifier suggests to the compiler that a function should be expanded inline, minimizing the overhead of function calls.

Constexpr Specifier

The constexpr specifier, introduced in C 11, serves a dual purpose: it guarantees that a function can be evaluated at compile-time and that it will return a constant expression.

Does constexpr Imply Inline?

Yes, according to the C 11 standard ([dcl.constexpr]): "constexpr functions and constexpr constructors are implicitly inline (7.1.2)."

Compiler Behavior

While constexpr implies inline, it's worth noting that the inline specifier has limited influence on a compiler's inlining decisions. However, it does affect the one definition rule, ensuring that constexpr functions are treated similarly to inline functions.

Evolution of Constexpr

Although constexpr initially implied functions suitable for inlining, its rules have expanded in subsequent C versions, allowing its application to more complex functions.

Conclusion

In summary, constexpr implies inline in the sense that the compiler can potentially inline a constexpr function as if the inline specifier were explicitly present. However, factors beyond constexpr's implication may influence a compiler's decision to inline a function.

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