ERRSTR(3) ERRSTR(3)
NAME
errstr, rerrstr, werrstr - description of last system call
error
SYNOPSIS
#include <u.h>
#include <libc.h>
int errstr(char *err, uint nerr)
void rerrstr(char *err, uint nerr)
void werrstr(char *fmt, ...)
DESCRIPTION
When a system call fails it returns -1 and records a null
terminated string describing the error in a per-process
buffer. Errstr swaps the contents of that buffer with the
contents of the array err. Errstr will write at most nerr
bytes into err; if the per-process error string does not
fit, it is silently truncated at a UTF character boundary.
The returned string is NUL-terminated. Usually errstr will
be called with an empty string, but the exchange property
provides a mechanism for libraries to set the return value
for the next call to errstr.
The per-process buffer is ERRMAX bytes long. Any error
string provided by the user will be truncated at ERRMAX-1
bytes. ERRMAX is defined in <libc.h>.
If no system call has generated an error since the last call
to errstr with an empty string, the result is an empty
string.
The verb r in print(3) calls errstr and outputs the error
string.
Rerrstr reads the error string but does not modify the per-
process buffer, so a subsequent errstr will recover the same
string.
Werrstr takes a print style format as its argument and uses
it to format a string to pass to errstr. The string returned
from errstr is discarded.
The error string is maintained in parallel with the Unix
error number errno. Changing errno will reset the error
string, and changing the error string via errstr or werrstr
will reset errno.
Page 1 Plan 9 (printed 12/22/24)
ERRSTR(3) ERRSTR(3)
SOURCE
/usr/local/plan9/src/lib9/errstr.c
DIAGNOSTICS
Errstr always returns 0.
SEE ALSO
intro(3), perror(3)
BUGS
The implementation sets errno to the (somewhat arbitrary)
constant 0x19283745 when the error string is valid. When
errno is set to other values, the error string is synthe-
sized using strerror(3).
Page 2 Plan 9 (printed 12/22/24)