|ERRNO(3)||Library Functions Manual||ERRNO(3)|
#define errno <object of thread local storage duration>
At program startup, the runtime shall initialize errno to contain the value zero (the initial value in other threads is undefined). It is guaranteed that no function provided by the C standard library shall set the value of errno to zero; therefore, for functions which do not have a unique return value for indicating error, it is possible to determine whether an error occured by setting errno to zero before the call, then after the call seeing if an error value has been stored into errno.
In some historical versions of the POSIX standard, the prescribed method of using errno was to define extern int errno. This is no longer supported by the POSIX or C standards, and will not work on the majority of implementations, including this one.
|February 20, 2013||Fusion|