errstr, rerrstr, werrstr - description of last system call error #include <u.h>

#include <libc.h>

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 <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 (2) 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.

/sys/src/libc/9syscall

/sys/src/libc/9sys/werrstr.c

Errstr always returns 0. intro (2), perror (2)