Can you construct and pass a variable argument list to a variadic function at run time in standard C, or must you instead use a va_list and call a corresponding v* function (such as vprintf)?

Introduction / Context:
The ellipsis “...” in C is a compile-time feature. Call sites fix the number and types of arguments syntactically; there is no portable facility to construct an argument pack at run time and pass it to an arbitrary variadic function. Instead, the standard pattern for forwarding is to use va_list with the v* versions of APIs.

Given Data / Assumptions:

• Variadic functions like printf(const char fmt, ...) have companions like vprintf(const char fmt, va_list ap).
• va_list encapsulates the traversal state for an existing variadic call.

Concept / Approach:
To “pass along” a variadic sequence, write your function as variadic too, create a va_list with va_start, and then call a v function, e.g., vprintf(fmt, ap). You cannot, in portable C, generate a fresh “...” argument list dynamically; ABIs and calling conventions prevent standardizing such behavior.

Step-by-Step Solution:
Define wrapper: void logf(const char fmt, ...).Inside: va_list ap; va_start(ap, fmt);Forward: vprintf(fmt, ap);Cleanup: va_end(ap).

Verification / Alternative check:
Inspect standard library: every variadic family has a v counterpart that accepts va_list (vfprintf, vsnprintf, etc.). That is the endorsed mechanism for run-time forwarding.

Why Other Options Are Wrong:
“Yes, synthesize ... dynamically” is nonportable/incorrect. Hardware width, integer-only limitations, or C++ do not change the C rule; even in C++ the recommended approach uses va_list or variadic templates (a different language feature).

Common Pitfalls:
Trying to cast a pointer to emulate arguments, or assuming you can create a fake stack frame; this is undefined behavior.

Final Answer:
No, you cannot build “...” at run time; use va_list with a v function