t_errno - XTI error return value
t_errno is used by XTI functions to return error values.
XTI functions provide an error number in t_errno which has type int and is defined in <xti.h>. The value of t_errno will be defined only after a call to a XTI function for which it is explicitly stated to be set and until it is changed by the next XTI function call. The value of t_errno should only be examined when it is indicated to be valid by a function's return value. Programs should obtain the definition of t_errno by the inclusion of <xti.h>. The practice of defining t_errno in program as externin t_errno is obsolescent. No XTI function sets t_errno to 0 to indicate an error.
It is unspecified whether t_errno is a macro or an identifier with external linkage. It represents a modifiable lvalue of type int. If a macro definition is suppressed in order to access an actual object or a program defines an identifier with name t_errno, the behavior is undefined.
The symbolic values stored in t_errno by an XTI function are defined in the ERRORS sections in all relevant XTI function definition pages.