|ERRNO(3P)||POSIX Programmer's Manual||ERRNO(3P)|
Many functions provide an error number in errno, which has type int and is defined in <errno.h>. The value of errno shall be defined only after a call to a function for which it is explicitly stated to be set and until it is changed by the next function call or if the application assigns it a value. The value of errno should only be examined when it is indicated to be valid by a function's return value. Applications shall obtain the definition of errno by the inclusion of <errno.h>. No function in this volume of POSIX.1‐2008 shall set errno to 0. The setting of errno after a successful call to a function is unspecified unless the description of that function specifies that errno shall not be modified.
It is unspecified whether errno is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual object, or a program defines an identifier with the name errno, the behavior is undefined.
The symbolic values stored in errno are documented in the ERRORS sections on all relevant pages.
The following sections are informative.
An application that needs to examine the value of errno to determine the error should set it to 0 before a function call, then inspect it before a subsequent function call.
The Base Definitions volume of POSIX.1‐2008, <errno.h>
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
|2013||IEEE/The Open Group|