Boost C++ Libraries: Ticket #4946: Uninitialized variable warning in lexical_cast.hpp

attachment set

Tue, 07 Dec 2010 19:01:43 GMT

attachment → lexical_cast.hpp.diff

Tue, 07 Dec 2010 19:28:59 GMT

The attached patch will generate another self assignment warning.

owner, status changed

Antony Polukhin — Fri, 13 May 2011 09:56:48 GMT

owner changed from nasonov to Antony Polukhin
status new → assigned

Antony Polukhin — Sat, 14 May 2011 07:58:30 GMT

Some time ago, I saw that bug. But now I can not reproduce it.
If you still get this bug, please test the following patch, and write about the results

attachment set

Antony Polukhin — Sat, 14 May 2011 07:59:16 GMT

attachment → lexical_cast.diff

New fix

status changed; resolution set

Antony Polukhin — Thu, 08 Dec 2011 15:39:08 GMT

status assigned → closed
resolution → worksforme

A lot of things have changed in lexical_cast since 1.44 version. Now, I can not reproduce this warning.

status, version changed; resolution deleted

eduardorp1@… — Tue, 17 Jun 2014 19:06:36 GMT

status closed → reopened
version Boost 1.44.0 → Boost 1.55.0
resolution worksforme

Still happens on Mac OS X 10.9.

Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.2.0
In file included from /Users/epoyart/projects/(...)/main.cpp:15:
In file included from /opt/local/include/boost/program_options.hpp:15:
In file included from /opt/local/include/boost/program_options/options_description.hpp:13:
In file included from /opt/local/include/boost/program_options/value_semantic.hpp:14:
/opt/local/include/boost/lexical_cast.hpp:2377:24: warning: variable 'result' may be uninitialized when used here [-Wconditional-uninitialized]
                return result;
                       ^~~~~~
/opt/local/include/boost/lexical_cast.hpp:2543:29: note: in instantiation of member function 'boost::detail::lexical_cast_do_cast<int, std::__1::basic_string<char> >::lexical_cast_impl' requested here
        return caster_type::lexical_cast_impl(arg);
                            ^
In file included from /Users/epoyart/projects/(...)/main.cpp:15:
In file included from /opt/local/include/boost/program_options.hpp:15:
In file included from /opt/local/include/boost/program_options/options_description.hpp:13:
In file included from /opt/local/include/boost/program_options/value_semantic.hpp:418:
/opt/local/include/boost/program_options/detail/value_semantic.hpp:89:21: note: in instantiation of function template specialization 'boost::lexical_cast<int, std::__1::basic_string<char> >' requested here
            v = any(lexical_cast<T>(s));
                    ^
/opt/local/include/boost/program_options/detail/value_semantic.hpp:170:13: note: in instantiation of function template specialization 'boost::program_options::validate<int, char>' requested here
            validate(value_store, new_tokens, (T*)0, 0);
            ^
/opt/local/include/boost/program_options/detail/value_semantic.hpp:185:33: note: in instantiation of member function 'boost::program_options::typed_value<int, char>::xparse' requested here
        typed_value<T>* r = new typed_value<T>(v);
                                ^
/Users/epoyart/projects/(...)/main.cpp:39:24: note: in instantiation of function template specialization 'boost::program_options::value<int>' requested here
        ("num_images", value<int>(&numImages)->default_value(0), "number of images to convert; 0 = all")
                       ^
In file included from /Users/epoyart/projects/(...)/main.cpp:15:
In file included from /opt/local/include/boost/program_options.hpp:15:
In file included from /opt/local/include/boost/program_options/options_description.hpp:13:
In file included from /opt/local/include/boost/program_options/value_semantic.hpp:14:
/opt/local/include/boost/lexical_cast.hpp:2366:30: note: initialize the variable 'result' to silence this warning
                Target result;
                             ^
                              = 0
1 warning generated.

Maxim.Yanchenko@… — Tue, 09 Sep 2014 10:48:12 GMT

same in boost 1.56.0 compiled with gcc4.8.2, lexical_cast.hpp:2314:16:

    template <typename Target, typename Source>
    inline Target lexical_cast(const Source &arg)
    {
        Target result;     // <<<<< line 2314
        if (!boost::conversion::detail::try_lexical_convert(arg, result))
            BOOST_LCAST_THROW_BAD_CAST(Source, Target);
        return result;
    }

which I believe goes down to the line 2083:

            static inline bool try_convert(const Source& arg, Target& result) {
                i_interpreter_type i_interpreter;
                // Disabling ADL, by directly specifying operators.
                if (!(i_interpreter.operator <<(arg)))
                    return false;     // <<<<< line 2083

P.S. It looks like a GCC bug, to me, as I see in the preprocessed output that throw_exception is noreturn so GCC should see that the whole lexical_cast function is noreturn if try_convert returns false:

template<class E> __attribute__ ((__noreturn__)) inline void throw_exception( E const & e )

ytizikc@… — Thu, 14 May 2015 22:44:11 GMT

Interestingly I've been able to reproduce this for boost 1.56 on Linux running gcc 4.8.2 when using the -O0 -Og -g3 flags, but not when using just plain -O0 (not follows by -Og), nor with -O3 (naturally without -Og -g3) used.

yitzikc@… — Thu, 14 May 2015 22:53:34 GMT

Antony Polukhin — Fri, 25 Sep 2015 17:51:51 GMT

Another attempt to fix the issue in develop branch

anonymous — Fri, 22 Jul 2016 09:00:36 GMT

I'm also seeing this issue with gcc 4.8.4 and boost 1.56 but only when -Og is used.

For me the warnings are reported at the point where lexical cast is used rather than in the boost header, so our usual warning suppressions don't do anything. I've tried adding the suggested #pragma GCC diagnostic push stuff around our include of boost/lexical_cast.hpp but it also has no effect.

The only way I've found to get around it is to disable -Wuninitialized in debug builds.

martin.braun@… — Tue, 29 Nov 2016 02:25:44 GMT

Can still confirm with gcc 5.4.0 and Boost 1.58:

#include <boost/lexical_cast.hpp>
#include <iostream>
#include <vector>
#include <string>
int main(void)
{
    std::vector<int> v;
    std::string s("5");
    v.push_back(boost::lexical_cast<int>(s));
    return 0;
}

$ g++ -Og -Wall warning.cpp
warning.cpp: In function ‘int main()’:
warning.cpp:10:16: warning: ‘result’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     v.push_back(boost::lexical_cast<int>(s));

Martin — Tue, 13 Dec 2016 18:00:47 GMT

Is there a reason not to explicitly default-initialize 'result'? One of the earlier patches was to do just that. Basically, the safe equivalent of

Target result = Target();

status, milestone changed; resolution set

Antony Polukhin — Fri, 27 Jan 2017 18:58:35 GMT

status reopened → closed
resolution → fixed
milestone To Be Determined → Boost 1.61.0

Fixed in e6adec14, merged to master and released in Boost 1.61