buffer interface violates strict-aliasing rule

[Vinnie Falco <vinnie.falco@…>]

The buffer class interfaces can cause violations of the strict-aliasing rule. This example program emits this warning when compiled with optimizations on GCC 5.1.1:

#include <boost/asio/streambuf.hpp>
#include <boost/endian/buffers.hpp>
#include <cstdint>
#include <memory>

template<class Streambuf>
std::uint16_t
get(Streambuf& sb)
{
    using namespace boost::asio;
    using namespace boost::endian;
    std::uint8_t b[2];
    sb.consume(buffer_copy(buffer(b), sb.data()));
    return reinterpret_cast<big_uint16_buf_t const*>(&b[0])->value();
}

int main()
{
    using namespace boost::asio;
    streambuf sb;
    std::uint8_t b[2];
    memset(&b[0], 0, sizeof(b));
    sb.commit(buffer_copy(sb.prepare(sizeof(b)), buffer(b)));
    return get(sb);
}

Produces:

prog.cc: In instantiation of 'uint16_t get(Streambuf&)
[with Streambuf = boost::asio::basic_streambuf<>; uint16_t = short unsigned int]':
prog.cc:24:18:   required from here
prog.cc:14:67: warning: dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]
     return reinterpret_cast<big_uint16_buf_t const*>(&b[0])->value();

Link to program and output: ​http://melpon.org/wandbox/permlink/x7xQsxaU3jv0lOtD