Re: [boost] [xpressive] Significant compiler warning

Subject: Re: [boost] [xpressive] Significant compiler warning
From: Eric Niebler (eric_at_[hidden])
Date: 2009-11-25 21:06:57

Ian Emmons wrote:
> I have a program that uses Boost.Xpressive.  When compiling this code on the Macintosh with the darwin-4.2.1 toolset, I get the following compiler warning:
> 
>     .../boost_1_41_0/boost/xpressive/traits/cpp_regex_traits.hpp:84:
>     warning: left shift count >= width of type
> 
> Here is the offending line of code:
> 
>     umaskex_t const highest_bit = 1
>         << (sizeof(umaskex_t) * CHAR_BIT - 1);
> 
> The problem (if my thinking cap is screwed on correctly) is that the 1 that is being shifted is of type int, and is not converted to the target type of umaskex_t until after the shift operation.  I believe that this should be changed to the following to avoid highest_bit being set to zero:
> 
>     umaskex_t const highest_bit = static_cast<umaskex_t>(1)
>         << (sizeof(umaskex_t) * CHAR_BIT - 1);

Seems right to me. I'll make the change. Thanks.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com