Can Valid Code in Both C and C Produce Different Output When Compiled?

Can Code Valid in Both C and C Exhibit Divergent Behavior When Compiled?

Despite numerous similarities, there are subtle differences between C and C . This raises the question: can code valid in both languages still produce different outcomes when compiled with their respective standard compilers?

Preconditions for a Fair Comparison

To ensure a meaningful comparison, let's establish certain conditions:

• Preprocessor directives (e.g., #ifdef) are excluded.
• Implementation-defined aspects are identical in both languages.
• Modern versions of the standards are compared (e.g., C90 or later and C 98).

A Behavioral Disparity

Consider the following code snippet:

#include <stdio.h>

struct f { int x; };

int main() {
    f();
}

int f() {
    return printf("hello");
}

In C , this code will result in no output, as a temporary f object is created and destroyed. However, in C90, it will print "hello" because functions can be invoked without prior declaration.

This variance arises from the distinct interpretations of f() in C and C . In C, f() is treated as a function call, while in C , it's considered a declaration of a struct.

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