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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
NAME
perror — write error messages to standard error
SYNOPSIS
#include <stdio.h> void perror(const char *s);
DESCRIPTION
The functionality described on this reference page is aligned with the ISO C standard. Any conflict
between the requirements described here and the ISO C standard is unintentional. This volume of
POSIX.1‐2017 defers to the ISO C standard.
The perror() function shall map the error number accessed through the symbol errno to a language-
dependent error message, which shall be written to the standard error stream as follows:
* First (if s is not a null pointer and the character pointed to by s is not the null byte), the string
pointed to by s followed by a <colon> and a <space>.
* Then an error message string followed by a <newline>.
The contents of the error message strings shall be the same as those returned by strerror() with argument
errno.
The perror() function shall mark for update the last data modification and last file status change
timestamps of the file associated with the standard error stream at some time between its successful
completion and exit(), abort(), or the completion of fflush() or fclose() on stderr.
The perror() function shall not change the orientation of the standard error stream.
On error, perror() shall set the error indicator for the stream to which stderr points, and shall set
errno to indicate the error.
Since no value is returned, an application wishing to check for error situations should call
clearerr(stderr) before calling perror(), then if ferror(stderr) returns non-zero, the value of errno
indicates which error occurred.
RETURN VALUE
The perror() function shall not return a value.
ERRORS
Refer to fputc().
The following sections are informative.
EXAMPLES
Printing an Error Message for a Function
The following example replaces bufptr with a buffer that is the necessary size. If an error occurs, the
perror() function prints a message and the program exits.
#include <stdio.h>
#include <stdlib.h>
...
char *bufptr;
size_t szbuf;
...
if ((bufptr = malloc(szbuf)) == NULL) {
perror("malloc"); exit(2);
}
...
APPLICATION USAGE
Application writers may prefer to use alternative interfaces instead of perror(), such as strerror_r() in
combination with fprintf().
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
fprintf(), fputc(), psiginfo(), strerror()
The Base Definitions volume of POSIX.1‐2017, <stdio.h>
COPYRIGHT
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 .