NAME
perror, strerror,
strerror_r, sys_errlist,
sys_nerr —
system error messages
LIBRARY
library “libc”
SYNOPSIS
#include
<stdio.h>
void
perror(const char *s);
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
The
strerror(),
strerror_r(), and perror()
functions look up the 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 s is non-NULL
and does not point to the null 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.
If the error number is not recognized, these
functions return an error message string containing
“Unknown error: ” followed by
the error number in decimal. The
strerror()
and strerror_r() functions return
EINVAL as a warning. 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 strerror() and
perror() functions first appeared in
4.4BSD. The strerror_r()
function was implemented in FreeBSD 4.4 by
Wes Peters ⟨wes@FreeBSD.org⟩.
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.