1PERROR(3P)                 POSIX Programmer's Manual                PERROR(3P)
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PROLOG

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

12       perror — write error messages to standard error
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SYNOPSIS

15       #include <stdio.h>
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17       void perror(const char *s);
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DESCRIPTION

20       The functionality described on this reference page is aligned with  the
21       ISO C  standard.  Any  conflict between the requirements described here
22       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2017
23       defers to the ISO C standard.
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25       The  perror()  function shall map the error number accessed through the
26       symbol errno to a language-dependent  error  message,  which  shall  be
27       written to the standard error stream as follows:
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29        *  First (if s is not a null pointer and the character pointed to by s
30           is not the null byte), the string pointed to by  s  followed  by  a
31           <colon> and a <space>.
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33        *  Then an error message string followed by a <newline>.
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35       The  contents  of  the error message strings shall be the same as those
36       returned by strerror() with argument errno.
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38       The perror() function shall mark for update the last data  modification
39       and  last file status change timestamps of the file associated with the
40       standard error stream at some time between  its  successful  completion
41       and  exit(),  abort(),  or  the  completion  of fflush() or fclose() on
42       stderr.
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44       The perror() function shall not change the orientation of the  standard
45       error stream.
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47       On  error,  perror()  shall  set  the error indicator for the stream to
48       which stderr points, and shall set errno to indicate the error.
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50       Since no value is returned, an application wishing to check  for  error
51       situations  should  call clearerr(stderr) before calling perror(), then
52       if ferror(stderr) returns non-zero, the value of errno indicates  which
53       error occurred.
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RETURN VALUE

56       The perror() function shall not return a value.
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ERRORS

59       Refer to fputc().
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61       The following sections are informative.
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EXAMPLES

64   Printing an Error Message for a Function
65       The  following example replaces bufptr with a buffer that is the neces‐
66       sary size. If an error occurs, the perror() function prints  a  message
67       and the program exits.
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70           #include <stdio.h>
71           #include <stdlib.h>
72           ...
73           char *bufptr;
74           size_t szbuf;
75           ...
76           if ((bufptr = malloc(szbuf)) == NULL) {
77               perror("malloc"); exit(2);
78           }
79           ...
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APPLICATION USAGE

82       Application writers may prefer to use alternative interfaces instead of
83       perror(), such as strerror_r() in combination with fprintf().
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RATIONALE

86       None.
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FUTURE DIRECTIONS

89       None.
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SEE ALSO

92       fprintf(), fputc(), psiginfo(), strerror()
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94       The Base Definitions volume of POSIX.1‐2017, <stdio.h>
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97       Portions of this text are reprinted and reproduced in  electronic  form
98       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
99       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
100       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
101       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
102       event of any discrepancy between this version and the original IEEE and
103       The Open Group Standard, the original IEEE and The Open Group  Standard
104       is  the  referee document. The original Standard can be obtained online
105       at http://www.opengroup.org/unix/online.html .
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107       Any typographical or formatting errors that appear  in  this  page  are
108       most likely to have been introduced during the conversion of the source
109       files to man page format. To report such errors,  see  https://www.ker
110       nel.org/doc/man-pages/reporting_bugs.html .
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114IEEE/The Open Group                  2017                           PERROR(3P)
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