#include <errno.h>#include <stdio.h>#include <string.h> #define	UPREFIX		"Unknown error: " /* * Define a buffer size big enough to describe a 64-bit signed integer * converted to ASCII decimal (19 bytes), with an optional leading sign * (1 byte); finally, we get the prefix and a trailing NUL from UPREFIX. */#define	EBUFSIZE	(20 + sizeof(UPREFIX)) /* * Doing this by hand instead of linking with stdio(3) avoids bloat for * statically linked binaries. */static voiderrstr(int num, char *buf, size_t len){	char *t;	unsigned int uerr;	char tmp[EBUFSIZE]; 	t = tmp + sizeof(tmp);	*--t = '\0';	uerr = (num >= 0) ? num : -num;	do {		*--t = "0123456789"[uerr % 10];	} while (uerr /= 10);	if (num < 0)		*--t = '-';	strlcpy(buf, UPREFIX, len);	strlcat(buf, t, len);} char *strerror(int num){	static char ebuf[EBUFSIZE]; 	if (num > 0 && num < sys_nerr)		return ((char *)sys_errlist[num]);	errno = EINVAL;	errstr(num, ebuf, sizeof(ebuf));	return (ebuf);}