## Static Member Function Pointers as C API Callbacks: A Safety and Portability Dilemma?

Static Member Function Pointers as Callbacks in C APIs: A Safety and Portability Dilemma

Using static member function pointers as C API callbacks in C raises concerns about safety and portability. While such a practice may appear to function initially, as class-static functions frequently adopt the same calling convention as C functions, it is considered unsafe and inadvisable per the C standard.

According to the standard (3.5/10), "the types specified by all declarations referring to a given object or function shall be identical." However, if a static member function is employed as a callback target, the callback code using C language bindings will require a function with a different language linkage. As defined in the standard (7.5/1), "Two function types with different language linkages are distinct types even if they are otherwise identical."

Therefore, the static member function and the API callback must share the same language linkage. To ensure safety and portability, it is strongly recommended to declare C ABI callbacks as "extern "C"" in C code.

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