[optional] Warnings about uninitialized values

21 Jun 2014

      Hi,

When I use boost::optional I often see gcc warnings about using possibly 
uninitialized values. I've seen such warnings in my projects outside Boost but 
now I encountered them in Boost.Log. Building the current develop with gcc 4.8 
I see this:

./boost/date_time/constrained_value.hpp: In member function 
‘boost::shared_ptrboost::log::v2_mt_posix::sinks::sink 
boost::log::v2_mt_posix::
{anonymous}::default_text_file_sink_factory<CharT>::create_sink(const 
settings_section&) [with CharT = wchar_t; boost::log::v2_mt_posix::
{anonymous}::default_text_file_sink_factory<CharT>::settings_section = 
boost::log::v2_mt_posix::basic_settings_section]’:
./boost/date_time/constrained_value.hpp:76:7: warning: ‘*((void*)& day +2)’ 
may be used uninitialized in this function [-Wmaybe-uninitialized]
       value_ = value;
       ^
libs/log/src/init_from_settings.cpp:172:32: note: ‘*((void*)& day +2)’ was 
declared here
     optional< unsigned short > day;
                                ^
libs/log/src/init_from_settings.cpp:249:87: warning: ‘*((void*)& weekday +4)’ 
may be used uninitialized in this function [-Wmaybe-uninitialized]
         return sinks::file::rotation_at_time_point(weekday.get(), hour, 
minute, second);
                                                                                       ^
libs/log/src/init_from_settings.cpp:171:37: note: ‘*((void*)& weekday +4)’ was 
declared here
     optional< date_time::weekdays > weekday;
                                     ^
I attached the full log for convenience. The code in question is this 
function:

https://github.com/boostorg/log/blob/develop/src/init_from_settings.cpp#L171

Note that at line 248 and below I check that the optional is filled before 
using it, so there is no way I'll be accessing any uninitialized data (that 
is, if boost::optional behaves correctly).

I suspect this may be a compiler bug. I tried to create a minimal example to 
reproduce it but the warning doesn't show in a simple context. However, I'd 
like it to be worked around somehow (unless it's an actual bug in 
boost::optional).

Any suggestions? Am I missing a bug in my code?

Andrey Semashev

Adam Romanek

Andrey Semashev

Andrey Semashev

Andrzej Krzemienski

Andrey Semashev

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