id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
13554	NULL deference exception in boost::asio::ip::tcp::resolver::results_type	giacomopoz@…	chris_kohlhoff	"boost::asio::ip::tcp::resolver::results_type type triggers a NULL dereference exception when calling empty() on a default-initialized instance.

How to reproduce:
- instantiate a new boost::asio::ip::tcp::resolver::results_type class instance with the default parameterless constructor
- call the empty() method, it should return true
- notice the access violation crash triggered

Code example:
{{{#!c++
#include <boost/asio/ip/tcp.hpp>

int main(int /*argc*/, char** /*argv*/)
{
  boost::asio::ip::tcp::resolver::results_type test = boost::asio::ip::tcp::resolver::results_type();
  if (test.empty())
    printf(""ok"");
}
}}}

Boost version: 1.66 Windows x64 vc141

Issue analysis: empty() is implemented as 
{{{#!c++
bool empty() const BOOST_ASIO_NOEXCEPT
{
  return this->values_->empty();
}
}}}
but this->values_ returns NULL when the class is empty. A possible fix could be to NULL-check this->values_ and then call ->empty() (if still needed at all)
{{{#!c++
bool empty() const BOOST_ASIO_NOEXCEPT
{
  return !this->values_ || this->values_->empty();
}
}}}

Current workaround: I would suggest not to use .empty() at all currently but to rely on .begin() == .end() .

Note that even if the code example above looks quite meaningless, .empty() crashes causes issue for example when checking if an address can be resolved using ip::basic_resolver::resolve function. The documentation states ""An empty range is returned if an error occurs"" so one expects to be able to check if the range is empty.

P.S.: I had links to sources and documentation but the tracker kept saying ""Akismet says content is spam"". Please fix your tracker."	Bugs	new	To Be Determined	asio	Boost 1.66.0	Problem