NAME
perror, strerror,
strerror_r, sys_errlist,
sys_nerr —
system error messages
LIBRARY
library “libc”
SYNOPSIS
#include
<stdio.h>
void
perror(const
char *string);
#include
<errno.h>
extern const char * const sys_errlist[];
extern const int sys_nerr;
#include
<string.h>
char *
strerror(int
errnum);
int
strerror_r(int
errnum, char
*strerrbuf, size_t
buflen);
DESCRIPTION
Thestrerror(),
strerror_r(), and perror()
functions look up the language-dependent error message string corresponding to
an error number.
The
strerror()
function accepts an error number argument errnum and
returns a pointer to the corresponding message string.
The
strerror_r()
function renders the same result into strerrbuf for a
maximum of buflen characters and returns 0 upon
success.
The
perror()
function finds the error message corresponding to the current value of the
global variable errno
(intro(2)) and writes it, followed by a newline, to the standard error
file descriptor. If the argument string is
non-NULL and does not point to the nul character,
this string is prepended to the message string and separated from it by a
colon and space (“: ”);
otherwise, only the error message string is printed. Note that in most cases
the err(3) and warn(3) family of functions is preferable to
perror(); they are more flexible and also print the
program name.
If the error number is not recognized, these
functions pass an error message string containing
“Unknown error: ” followed by
the error number in decimal. To warn about this,
strerror()
sets errno to EINVAL, and
strerror_r() returns EINVAL.
Error numbers recognized by this implementation fall in the range 0 <
errnum < sys_nerr.
If insufficient storage is provided in
strerrbuf (as specified in
buflen) to contain the error string,
strerror_r()
returns ERANGE and strerrbuf
will contain an error message that has been truncated and
NUL terminated to fit the length specified by
buflen.
The message strings can be accessed directly using
the external array sys_errlist. The external value
sys_nerr contains a count of the messages in
sys_errlist. The use of these variables is deprecated;
strerror()
or strerror_r() should be used instead.
SEE ALSO
STANDARDS
The perror() and
strerror() functions conform to
ISO/IEC 9899:1999 (“ISO C99”).
The strerror_r() function conforms to
IEEE Std 1003.1-2001 (“POSIX.1”).
HISTORY
The perror() function first appeared in
Version 4 AT&T UNIX. The
strerror() function first appeared in
4.3BSD-Reno. The
strerror_r() function first appeared in
NetBSD 4.0.
BUGS
For unknown error numbers, the strerror()
function will return its result in a static buffer which may be overwritten
by subsequent calls.
The return type for strerror() is missing
a type-qualifier; it should actually be const char
*.
Programs that use the deprecated sys_errlist variable often fail to compile because they declare it inconsistently.