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@(#)strerror.3 8.1 (Berkeley) 6/9/93
$FreeBSD: head/lib/libc/string/strerror.3 84306 2001-10-01 16:09:29Z ru $
.Dd June 9, 1993 .Dt STRERROR 3 .Os .Sh NAME .Nm perror , .Nm strerror , .Nm sys_errlist , .Nm sys_nerr .Nd system error messages .Sh LIBRARY .Lb libc .Sh SYNOPSIS n stdio.h .Ft void .Fn perror "const char *string" .Vt extern const char * const sys_errlist[] ; .Vt extern const int sys_nerr ; n 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.
p The .Fn strerror function accepts an error number argument .Fa errnum and returns a pointer to the corresponding message string.
p The .Fn perror function finds the error message corresponding to the current value of the global variable .Va errno
q Xr intro 2 and writes it, followed by a newline, to the standard error file descriptor. If the argument .Fa string is
f 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
q Ql : ; otherwise, only the error message string is printed.
p If .Fa errnum is not a recognized error number, the error message string will contain .Dq Li "Unknown error: " followed by the error number in decimal.
p 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 x 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.
p Programs that use the deprecated .Va sys_errlist variable often fail to compile because they declare it inconsistently.