Why doesn't GCC show any errors on an anonymous variable?

Question

I read this question that explains how anonymous variables are invalid in C++.

But the following program compiles without any warning or errors on GCC 7.2 (even with -Wall) - demo:

int main() {
    int (*); // anonymous variable?
}

Here, this is apparently also an integer type anonymous variable. So, why GCC does not show any errors or warnings? Is this a GCC bug?

[This](https://godbolt.org/g/dV14P1) is indeed surprising. @Jayesh Write all relevant information in your question. — Passer By, Oct 31 '17 at 07:33
Indeed, with `-c -Wall -Wextra` the `g++-7` compiler says nothing but `clang++-5.0` gives an error: *expected expression* on the closing paren. Perhaps it might be some compiler bug (I don't know who is wrong). — Basile Starynkevitch, Oct 31 '17 at 07:37
It seems the "buggy" behaviour only appears when parentheses are used — Passer By, Oct 31 '17 at 07:39
@PasserBy - Parentheses with an asterisk. Removing the asterisk [produces a warning](https://godbolt.org/g/ENJsrb). — StoryTeller - Unslander Monica, Oct 31 '17 at 07:52
@StoryTeller Since its being parsed as creating a temporary `int`, I'd say its not the same thing — Passer By, Oct 31 '17 at 07:53
I didn't check this case at all, but gcc has weak heuristics to disable warnings in some cases: - has already been warned about, - is between parentheses, - is unnamed, etc. — Marc Glisse, Oct 31 '17 at 07:53
@PasserBy - Is it creating a temporary? `int()` is a function type. The plot thickens — StoryTeller - Unslander Monica, Oct 31 '17 at 07:53
@PasserBy - Furthermore, [forcing it to be a temporary (by replacing `()` with `{}`)](https://godbolt.org/g/dy3Krb), produces absolutely no diagnostic. — StoryTeller - Unslander Monica, Oct 31 '17 at 07:55
@StoryTeller I'm confused :) For argument's sake, since there should be no such thing as anonymous function declarations and hence it should be parsed as an expression statement. I have no idea what's going on with `{}` — Passer By, Oct 31 '17 at 08:00
@PasserBy - Well, I think GCC is confused as well. `int()` is a type, just like `int*` is a type. They should produce identical errors. And yet, they don't. `int{}` is just some added silliness. — StoryTeller - Unslander Monica, Oct 31 '17 at 08:01

Oliver Strong · Answer 1 · 2017-10-31T07:43:50.613

5

There have been bugs recorded with gcc and how it detects variables for example I was using it to compile a simple program and it gave an error saying variable may be uninitialized when it have been. It is just a bug in the compiler. For example see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55985

edited Oct 31 '17 at 07:43

answered Oct 31 '17 at 07:40

Oliver Strong

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The response was the issue has been fixed since at least gcc 5.3. OP's problem persists even for gcc 7.2 – Passer By Oct 31 '17 at 07:44
The problem does still persist as I have encountered this error in 7.2 the bug may have just been fixed in this individual case or something broke in a later update. – Oliver Strong Oct 31 '17 at 07:46

Why doesn't GCC show any errors on an anonymous variable?

1 Answers1