Question

Could you guys help me decypher unknown exception that is thrown by boost::iostreams::mapped_file_sink ?

My configuration

• boost 1.51
• Visual Studio 2012 on Windows 7
• GCC 4.7 on Ubuntu

Here is the code I have

try
{
    boost::iostreams::mapped_file_params params_;
    boost::iostreams::mapped_file_sink sink_;
    params_.length = 0;
    params_.new_file_size = 1024;
    params_.path = "./test.bin";
    sink_.open(params_);
    sink_.close();
}
catch (std::ios::failure& ex)
{
    std::cout << "\t" << "what: " << ex.what() << "\n";
}
catch (std::system_error& ex)
{
    std::cout << "\t" << "code: " << ex.code() << "  what: " << ex.what() << "\n";
}
catch (std::runtime_error& ex)
{
    std::cout << "\t" << ex.what() << "\n";
}
catch (boost::archive::archive_exception& ex)
{
    std::cout << "\t" << ex.what() << "\n";
}
catch (boost::exception& ex)
{
    std::cout << "blah\n";
}
catch (std::exception& ex)
{
    std::cout << "\t" << ex.what() << " --- " << typeid(ex).name() << "\n";
}

It always works in Windows.

In Ubuntu it creates empty file of given size but throws exception on open(). Subsequent execution of the code if exists doesn’t cause exception.

The worst part is that I can’t see the reason of the exception. I can only catch std::exception whose what() returns meaningless “std::exception”.

In desperate attempt to find out what’s wrong I output typeid(ex).name() which shows

N5boost16exception_detail10clone_implINS0_19error_info_injectorISt9exception

which according to Google means: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::exception> >

Any ideas what’s wrong?

Answer 1

After 50 mins of guessing I found out that problem was in length field. The documentation doesn’t say that but its default value has to be -1 as stated in source code

BOOST_STATIC_CONSTANT(size_type, max_length = static_cast<size_type>(-1));

I intuitively assumed that if I set new_file_size to be more than zero it would ignore length.