readn.c

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 */
}