Is there a way to use errno safely in a multi-threaded application? [duplicate]

Answer 1

man errno says:

errno is defined by the ISO C standard to be a modifiable lvalue of type int, and must not be explicitly declared; errno may be a macro. errno is thread-local; setting it in one thread does not affect its value in any other thread.

Answer 2

If your standard library is multithread aware, then it probably has a #define that changes errno into a function call that returns a thread-local error return value. However, to use this you generally must include <errno.h>, rather than relying on an extern declaration.

I found an article Thread-safety and POSIX.1 which addresses this very question.