ERRNO(3)                   POSIX Programmer's Manual                  ERRNO(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       errno -- error return value

SSYYNNOOPPSSIISS
       #include <errno.h>

DDEESSCCRRIIPPTTIIOONN
       The lvalue _e_r_r_n_o is used by many functions to return error values.

       Many functions provide an error number in _e_r_r_n_o, which has type iinntt and
       is defined in _<_e_r_r_n_o_._h_>.  The value of _e_r_r_n_o 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 _e_r_r_n_o should only be examined when it
       is indicated to be valid by a function's return value. Applications
       shall obtain the definition of _e_r_r_n_o by the inclusion of _<_e_r_r_n_o_._h_>.  No
       function in this volume of POSIX.1-2017 shall set _e_r_r_n_o to 0. The
       setting of _e_r_r_n_o after a successful call to a function is unspecified
       unless the description of that function specifies that _e_r_r_n_o shall not
       be modified.

       It is unspecified whether _e_r_r_n_o 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 _e_r_r_n_o, the behavior is undefined.

       The symbolic values stored in _e_r_r_n_o are documented in the ERRORS
       sections on all relevant pages.

RREETTUURRNN VVAALLUUEE
       None.

EERRRROORRSS
       None.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       Previously both POSIX and X/Open documents were more restrictive than
       the ISO C standard in that they required _e_r_r_n_o to be defined as an
       external variable, whereas the ISO C standard required only that _e_r_r_n_o
       be defined as a modifiable lvalue with type iinntt.

       An application that needs to examine the value of _e_r_r_n_o to determine
       the error should set it to 0 before a function call, then inspect it
       before a subsequent function call.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _S_e_c_t_i_o_n _2_._3, _E_r_r_o_r _N_u_m_b_e_r_s

       The Base Definitions volume of POSIX.1-2017, <<eerrrrnnoo..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       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 .



IEEE/The Open Group                  2017                             ERRNO(3)
