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@(#)strerror.3 8.1 (Berkeley) 6/9/93
$FreeBSD: head/lib/libc/string/strerror.3 136432 2004-10-12 14:52:52Z keramida $
.Dd October 12, 2004 .Dt STRERROR 3 .Os .Sh NAME .Nm perror , .Nm strerror , .Nm strerror_r , .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" .Ft int .Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen" .Sh DESCRIPTION The .Fn strerror , .Fn strerror_r 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 strerror_r function renders the same result into .Fa strerrbuf for a maximum of .Fa buflen characters and returns 0 upon success.
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 Dq Li ": " ; otherwise, only the error message string is printed.
p If the error number is not recognized, these functions return an error message string containing .Dq Li "Unknown error: " followed by the error number in decimal. The .Fn strerror and .Fn strerror_r functions return .Er EINVAL as a warning. Error numbers recognized by this implementation fall in the range 0 < .Fa errnum < .Fa sys_nerr .
p If insufficient storage is provided in .Fa strerrbuf (as specified in .Fa buflen ) to contain the error string, .Fn strerror_r returns .Er ERANGE and .Fa strerrbuf will contain an error message that has been truncated and .Dv NUL terminated to fit the length specified by .Fa buflen .
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 or .Fn strerror_r should be used instead. .Sh SEE ALSO .Xr intro 2 , .Xr psignal 3 .Sh STANDARDS The .Fn perror and .Fn strerror functions conform to .St -isoC-99 . The .Fn strerror_r function conforms to .St -p1003.1-2001 . .Sh HISTORY The .Fn strerror and .Fn perror functions first appeared in x 4.4 . The .Fn strerror_r function was implemented in .Fx 4.4 by .An Wes Peters Aq wes@FreeBSD.org . .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 The return type for .Fn strerror is missing a type-qualifier; it should actually be .Vt const char * .
p Programs that use the deprecated .Va sys_errlist variable often fail to compile because they declare it inconsistently.