C varargs across functions: identify the incorrect usage when forwarding varargs and misusing va_start. #include <stdio.h> #include <stdarg.h> void display(char *s, ...); void show(char *t, ...); int main() { display("Hello", 4, 12, 13, 14, 44); return 0; } void display(char s, ...) { show(s, ...); / attempt to forward ellipsis directly */ } void show(char t, ...) { int a; va_list ptr; va_start(ptr, s); / wrong anchor, should be 't' */ a = va_arg(ptr, int); printf("%f", a); }

Introduction / Context:
Forwarding variable arguments between functions requires care. You cannot “pass” ... directly; instead you must rebuild the call with explicit arguments or use va_list/va_copy. Moreover, va_start must reference the last named parameter in the definition's parameter list.

Given Data / Assumptions:

• display attempts show(s, ...), which is not valid C syntax for forwarding varargs.
• show calls va_start(ptr, s) even though its last named parameter is t, not s.
• printf("%f", a) prints an int with a %f specifier, which is also mismatched.

Concept / Approach:
The error most centrally tested is in show: va_start must be invoked as va_start(ptr, t), because t is the last named parameter. Additionally, forwarding from display requires building a va_list inside display and then either consuming it there or using va_copy to pass to show. Writing show(s, ...) is invalid.

Step-by-Step Solution:
Fix display to accept va_list forwarding: e.g., have show accept va_list or reconstruct arguments.In show, replace va_start(ptr, s) with va_start(ptr, t).Match printf format with type: use %d for int.

Verification / Alternative check:
Correct patterns include: void vshow(char *t, va_list ap); and calling it from display with va_start/va_copy.

Why Other Options Are Wrong:
Invalid function display() call is also problematic but the more concrete, immediate error flagged is within show (wrong va_start anchor and format mismatch). No error and other distractors ignore these standard violations.

Common Pitfalls:
Trying to forward ... literally, using the wrong identifier in va_start, and mismatching printf formats.

Final Answer:
Error: invalid function show() call