'warning C4709: comma operator within array index expression' - but no comma to be seen anywhere!

Question

Take this little example code:

struct Test{
    operator int() const{
        return 0;
    }
};

Test test(){
    return Test();
}

int main(){
    int arr[10];
    arr[test()] = 5;
}

Compiling under Visual Studio 2010 with /W4 generates said warning. Interestingly, if I add but a simple default constructor, the warning suddenly vanishes. Also, it only works in that constellation. If I remove the function call or don't return a user-defined type, the warning disappears. Also, as expected, GCC doesn't produce such a warning.

So, can I take this warning with the above code as a bug in Visual Studio or is there more to it than seems? Would be very surprising though, to say the least.

Edit: Created a bug report on Microsoft Connect.

I can reproduce this behavior on VC++ 2008. Although to be honest I have never run across this behavior in VC++ up to now, because I always define a constructor for my classes. — In silico, May 16 '11 at 00:17

score 5 · Accepted Answer · answered May 16 '11 at 00:08

5

Definitely it is a bug - misleading warning.

answered May 16 '11 at 00:08

c-smile

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'warning C4709: comma operator within array index expression' - but no comma to be seen anywhere!

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