readn.c

该代码为unix环境高级编程的源代码

#include	"ourhdr.h"

ssize_t						/* Read "n" bytes from a descriptor. */
readn(int fd, void *vptr, size_t n)
{
	size_t	nleft, nread;
	char	*ptr;

	ptr = vptr;
	nleft = n;
	while (nleft > 0) {
		if ( (nread = read(fd, ptr, nleft)) < 0)
			return(nread);		/* error, return < 0 */
		else if (nread == 0)
			break;				/* EOF */

		nleft -= nread;
		ptr   += nread;
	}
	return(n - nleft);		/* return >= 0 */
}