Linux 2.6 - man page for errno (linux section 3posix)
|Linux & Unix Commands - Search Man Pages
ERRNO(P) POSIX Programmer's Manual ERRNO(P)
errno - error return value
The lvalue errno is used by many functions to return error values.
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 defini-
tion of errno by the inclusion of <errno.h>. No function in this volume of
IEEE Std 1003.1-2001 shall set errno to 0.
It is unspecified whether errno is a macro or an identifier declared with external link-
age. 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
The following sections are informative.
Previously both POSIX and X/Open documents were more restrictive than the ISO C standard
in that they required errno to be defined as an external variable, whereas the ISO C stan-
dard required only that errno be defined as a modifiable lvalue with type int.
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.
Error Numbers , the Base Definitions volume of IEEE Std 1003.1-2001, <errno.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 ERRNO(P)
All times are GMT -4. The time now is 09:21 PM.