How to convert errno in UNIX to corresponding string?

How to convert errno in UNIX to corresponding string?

unix errno

unix

Which systems define EAGAIN and EWOULDBLOCK as different values?

unix posix errno

unix

Difference between EACCES and EPERM

c unix language-agnostic posix errno

unix

Should I use system_category or generic_category for errno on Unix?

unix error-handling c++11 errno system-error

unix

SO_ERROR vs. errno

c sockets unix errno getsockopt

unix