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

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.

perror — write error messages to standard error

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

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.

The perror() function shall not return a value.

Refer to fputc().

The following sections are informative.

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



fprintf(), fputc(), psiginfo(), strerror()

The Base Definitions volume of POSIX.1‐2017, <stdio.h>

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 .

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 .

2017 IEEE/The Open Group