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Subject: Re: [boost] [units] gcc warnings
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-06-15 13:03:42


Stewart, Robert wrote:
> Emil Dotchevski wrote:
>> On Tue, Jun 15, 2010 at 3:55 AM, Stewart, Robert
>> <Robert.Stewart_at_[hidden]> wrote:
>>> Jürgen Hunold wrote:
>>>> I start using Boost.Units for a new project and found some
>>>> annyoing warnings when compiling with "-Wall -Wextra" and
>>>> "-Wconversion"
>>>> /home/hunold/src/devel/boost/boost/units/io.hpp: In function 'int
>>>> boost::units::get_flags(std::ios_base&, int)':
>>>> /home/hunold/src/devel/boost/boost/units/io.hpp:163: warning:
>>>> conversion to
>>>> 'int' from 'long int' may alter its value [-Wconversion]
>>>> Patch using an explicit static_cast<int> for the return value
>>>> attached.
>>> Do you know that the long int value can never exceed the
>>> range of int? If not, the static_cast will simply mask the
>>> problem.
>> With or without the static_cast, if the long int value exceeds the
>> range of an int you're screwed. The only difference the cast makes is
>> that you won't get the warning.
> You snipped the part in which I suggested an exception to indicate the overflow. That leaves the error handling to the calling code.
>> The problem with using casts to silence warnings is that silencing the
>> warning is a side effect of altering of the behavior of what is
>> usually a correct program.
> I can't quite parse that, but I was advocating against the OP's plan to simply mask the conversion with a cast.
> I have to wonder if you actually meant to reply to the OP and not me.

Humph. Has anyone in this discussion actually looked at the
code in question?
a) There can be no overflow because the possible values are enumerated.
b) With the current code, the compiler will implicitly use a static_cast.

In Christ,
Steven Watanabe

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