o.z o.z - 2 months ago 17
C++ Question

boost log non-const bitfield compilation error (backward compatibility issue)

I took the example from http://www.boost.org/doc/libs/1_61_0/libs/log/example/doc/tutorial_trivial_flt.cpp and added a bitfield print:

#include <boost/log/core.hpp>
#include <boost/log/trivial.hpp>
#include <boost/log/expressions.hpp>

namespace logging = boost::log;

//[ example_tutorial_trivial_with_filtering
void init()
{
logging::core::get()->set_filter
(
logging::trivial::severity >= logging::trivial::info
);
}


struct BF {
unsigned int b : 8;
BF() : b(0) {}
};


int main(int, char*[])
{
init();

BF bf;
BOOST_LOG_TRIVIAL(info) << "An informational severity message " << bf.b;

return 0;
}
//]


With boost 1.61 I got a compilation error:


cannot bind bitfield 'bf.BF::b' to 'unsigned int&'


With boost 1.57 the code is compiled and run (prints: [2016-09-19 20:21:33.018112] [0x000007fd1d5be672] [info] An informational severity message 0)

notice that:


  1. cout of-course can handle this (so I think it is not just a backward compatibility issue, but a bug)

  2. boost 1.61 can handle const bitfield, e.g
    BOOST_LOG_TRIVIAL(info) << "An informational severity message " << BF().b;



I'm searching for workaround.
Suggestions?

o.z o.z
Answer

I found a workaround - overloading operator<< for record_ostream of all unsigned integers:

#include <sys/types.h>

namespace logging = boost::log;

typedef logging::basic_formatting_ostream<  logging::record_ostream::char_type > formatting_ostream_type;

logging::record_ostream& operator << (logging::record_ostream& strm, u_int8_t value) {
    static_cast< formatting_ostream_type& >(strm) << value;
    return strm;
}

logging::record_ostream& operator << (logging::record_ostream& strm, u_int16_t value) {
    static_cast< formatting_ostream_type& >(strm) << value;
    return strm;
}

logging::record_ostream& operator << (logging::record_ostream& strm, u_int32_t value) {
    static_cast< formatting_ostream_type& >(strm) << value;
    return strm;
}

logging::record_ostream& operator << (logging::record_ostream& strm, u_int64_t value) {
    static_cast< formatting_ostream_type& >(strm) << value;
    return strm;
}

The integers got copied (are taken by value) so there is no bind issue