Question

If I write a program like the following one, g++ and visual studio have the courtesy of warning me that the local variable a is never used :

int main()
{
    int a; // An unused variable? Warning! Warning!
}

If I remove the unused variable (to make the compiler happy), it leaves me with the following program :

int main()
{
    // An empty main? That's fine.
}

Now, I am left with a useless program.

Maybe I am missing something, but, if an unused variable is bad enough to raise a warning, why would an empty program be ok?

The example above is pretty simple. But in real life, if I have a big program with an empty main (because I forgot to put anything in it). Then having a warning should be a good thing, isn’t it.

Maybe I am missing an option in g++ or visual studio that can raise a warning/error when the main is empty?

Answer 1

The reason for this is simple, if there is no return statement in main it implicitly returns EXIT_SUCCESS, as defined by the standard.

So an empty main is fine, no return needed, no function calls needed, nothing.

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To answer the question why GCC doesn’t warn you is because warnings are there to help you with common mistakes. Leaving a variable unused can lead to confusing errors, and code bloat.

However forgetting entirely to write a main function isn’t a common mistake by anything but a beginner and isn’t worth warning about (because it’s entirely legal as well).