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ERRSTR(2) System Calls Manual ERRSTR(2)
errstr, rerrstr, werrstr - description of last system call error
int errstr(char *err, uint nerr)
void rerrstr(char *err, uint nerr)
void werrstr(char *fmt, ...)
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
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(2) calls errstr and outputs the error string.
Rerrstr reads the error string but does not modify the per-process buf‐
fer, so a subsequent errstr will recover the same string.
Werrstr takes a print style format as its argument and uses it to for‐
mat a string to pass to errstr. The string returned from errstr is
Errstr always returns 0.