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.\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
.\"
.TH STRERROR 3 "22 December 1997" GNO "Library Routines"
.SH NAME
.BR perror ,
.BR strerror ,
.BR sys_errlist ,
.BR sys_nerr ,
.BR _errnoText
\- system error messages
.SH SYNOPSIS
#include <stdio.h>
.sp 1
void
\fBperror\fR(const char *\fIstring\fR);
.sp 1
extern const char * const \fBsys_errlist\fR[];
.br
extern const int \fBsys_nerr\fR;
.sp 1
#include <string.h>
.sp 1
char *
\fBstrerror\fR(int \fIerrnum\fR);
.SH DESCRIPTION
The
.BR strerror 
and
.BR perror 
functions look up the error message string corresponding to an
error number.
.LP
The
.BR strerror 
function accepts an error number argument
.I errnum
and
returns a pointer to the corresponding
message string.
.LP
The
.BR perror 
function finds the error message corresponding to the current
value of the global variable
.IR errno
(see
.BR intro (2))
and writes it, followed by a newline, to the
standard error file descriptor.
If the argument
.I string
is non-NULL,
it is prepended to the message
string and separated from it by
a colon and space.
If
.I string
is
.BR NULL ,
only the error message string is printed.
.LP
If
.I errnum
is not a recognized error number,
the error message string will contain
.BR "unknown error:" ,
followed by the error number in decimal.
.LP
The message strings can be accessed directly using the external
array
.IR sys_errlist .
The external value
.IR sys_nerr
contains a count of the messages in
.IR sys_errlist .
For backwards compatibility with older versions of GNO,
.BR sys_errlist
can also be referenced through the variable 
.BR _errnoText ,
which has identical type.
The use of these variables is deprecated;
.BR strerror 
should be used instead.
.SH SEE ALSO
.BR intro (2),
.BR psignal (3)
.SH HISTORY
The
.BR strerror 
and
.BR perror 
functions first appeared in 4.4BSD.
.SH BUGS
For unknown error numbers, the
.BR strerror 
function will return its result in a static buffer which
may be overwritten by subsequent calls.
.LP
Programs that use the deprecated
.IR sys_errlist
variable often fail to compile because they declare it
inconsistently.