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- Is errno thread-safe? 8 answers
If you are writing a multi-threaded application that uses system/library calls that make use of errno to indicate the error type, is there a safe way to use errno? If not, is there some other way to indicate the type of error that occurred rather than just that an error has occurred?
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.
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.
来源：https://stackoverflow.com/questions/449778/is-there-a-way-to-use-errno-safely-in-a-multi-threaded-application