Re: position.hh compile error C4146 (VisualStudio 2017)

[Akim Demaille]

Hi!

> Le 18 août 2018 à 07:36, 長田偉伸 <address@hidden> a écrit :
> 
> [Description]
> 
>    I used flex to generate the source code.
>    After that, when I compiled using VisualStudio 2017, an error of
> C4146 occurred.
> 
>    I modified the file containing the error as follows.
> 
>        # (original) position.hh:111
>              return (0 < rhs || -static_cast<unsigned int>(rhs) < lhs
> 
>        # (edited) position.hh:111
>              return (0 < rhs || -1 * static_cast<unsigned int>(rhs) < lhs
> 
>    I compiled it again and confirmed that no error occurred
> 
> 
> [Environment]
>    OS: Windows10
>        Visual Studio 2017 (C++)
> 
>    Version: bison (GNU Bison) 3.0.5
> 
> 
> Thank you,

Amazing…

According to http://www.externsoft.ch/media/swf/cpp11-iso.html,
we have in the grammar of C++ (with focus on what matters here):

unary_expression:
        • postfix_expression
        • unary_operator cast_expression

cast_expression 
        • unary_expression
        • '(' type_id ')' cast_expression

unary_operator:
        • '+'
        • '-'

postfix_expression:
        • 'dynamic_cast' '<' type_id '>' '(' expression ')'
        • ‘static_cast' '<' type_id '>' '(' expression ')'

So it is my reading that Visual Studio is wrong here.

I don’t like the -1 *, could you please rather check that parens would suffice?

             return (0 < rhs || -(static_cast<unsigned int>(rhs)) < lhs

Thanks!