.\" Copyright (c) 1980, 1991, 1993
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.\" the American National Standards Committee X3, on Information
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.\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD$
.\"
.Dd June 9, 1993
.Dt STRERROR 3
.Os BSD 4
.Sh NAME
.Nm perror ,
.Nm strerror ,
.Nm sys_errlist ,
.Nm sys_nerr
.Nd system error messages
.Sh SYNOPSIS
.Fd #include <stdio.h>
.Ft void
.Fn perror "const char *string"
.Vt extern const char * const sys_errlist[];
.Vt extern const int sys_nerr;
.Fd #include <string.h>
.Ft char *
.Fn strerror "int errnum"
.Sh DESCRIPTION
The
.Fn strerror
and
.Fn perror
functions look up the error message string corresponding to an
error number.
.Pp
The
.Fn strerror
function accepts an error number argument
.Fa errnum
and
returns a pointer to the corresponding
message string.
.Pp
The
.Fn perror
function finds the error message corresponding to the current
value of the global variable
.Va errno
.Pq Xr intro 2
and writes it, followed by a newline, to the
standard error file descriptor.
If the argument
.Fa string
is
.Pf non- Dv 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
.Pq Ql \&:\ \& ;
otherwise, only the error message string is printed.
.Pp
If
.Fa errnum
is not a recognized error number,
the error message string will contain
.Dq Li "Unknown error:\0
followed by the error number in decimal.
.Pp
The message strings can be accessed directly using the external
array
.Va sys_errlist .
The external value
.Va sys_nerr
contains a count of the messages in
.Va sys_errlist .
The use of these variables is deprecated;
.Fn strerror
should be used instead.
.Sh SEE ALSO
.Xr intro 2 ,
.Xr psignal 3
.Sh HISTORY
The
.Fn strerror
and
.Fn perror
functions first appeared in
.Bx 4.4 .
.Sh BUGS
For unknown error numbers, the
.Fn strerror
function will return its result in a static buffer which
may be overwritten by subsequent calls.
.Pp
Programs that use the deprecated
.Va sys_errlist
variable often fail to compile because they declare it
inconsistently.