readn.c

来自「unix环境编程」· C语言 代码 · 共 24 行

#include "apue.h"

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

	nleft = n;
	while (nleft > 0) {
		if ((nread = read(fd, ptr, nleft)) < 0) {
			if (nleft == n)
				return(-1); /* error, return -1 */
			else
				break;      /* error, return amount read so far */
		} else if (nread == 0) {
			break;          /* EOF */
		}
		nleft -= nread;
		ptr   += nread;
	}
	return(n - nleft);      /* return >= 0 */
}