Boost 1.87.0: Construction of io_context throws std::out_of_range if errno=34 before call

[rndx21033]

Boost 1.87.0: Construction of io_context throws std::out_of_range if errno=34 before call:

---

#include
#include <boost/asio/io_context.hpp>
#include

int main()
{
errno=34; // this will result in the following call throwing an exception
boost::asio::io_context ctx(std::thread::hardware_concurrency());
}

The offending code is in "asio/impl/config.hpp". Calls to strtoull and strtoll are followed by a check for errno==ERANGE, but there is not check first that ensures that the errno is actually relevant and has been set by that call.

Due to ambiguity of whether a return of LONG_MIN/LLONG_MIN/LONG_MAX/LLONG_MAX is due to that value being parsed or due to under/overflow, it seems like the safest course is to set errno=0 before those calls. I have tested this and confirmed that it does avoid the issue.