Can Seemingly Inert C/C Code Behave Differently?

Can Seemingly Inert Code Behave Differently in C and C ?

In C and C , while the syntactic overlap is substantial, the nuances between the languages can lead to unexpected outcomes. Though code that adheres to both standards may seem innocuous, there are indeed scenarios where it can produce contrasting behavior when compiled under each language.

One striking example revolves around the subtle discrepancy between function calls and object declarations in C and C . In C90, functions can be invoked without prior declaration. However, in C , this practice is prohibited.

Consider the following snippet:

#include <stdio.h>

struct f { int x; };

int main() {
    f();
}

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

In C , this code remains silent because an ephemeral f object is created and subsequently destroyed, leaving no trace. However, in C90, the function f can be invoked due to its implicit declaration. As a result, "hello" is printed to the console.

This instance highlights the importance of understanding the subtle differences between C and C , even when the code appears to conform to both languages. By being aware of such nuances, programmers can avoid unexpected behavior and write code that functions seamlessly across different compilation environments.

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