readn writen readline函数源代码

当从网络读写时，网络中的缓冲机构可能造成返回值小于所要求读写的字数[1]。因而需要加入相应的处理机制。
 
  
 
  
/* include readn */
 
  
 
  
#include 
#include 

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

	ptr = vptr;
	nleft = n;
	while (nleft > 0) {
		if ( (nread = read(fd, ptr, nleft)) < 0) {
			if (errno == EINTR)
				nread = 0;		/* and call read() again */
			else
				return(-1);
		} else if (nread == 0)
			break;				/* EOF */

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

ssize_t
Readn(int fd, void *ptr, size_t nbytes)
{
	ssize_t		n;

	if ( (n = readn(fd, ptr, nbytes)) < 0)
		err_sys("readn error");
	return(n);
}
 
  
ssize_t writen (int fd, const void *buf, size_t num)
{
ssize_t res;
size_t n;
const char *ptr;


n = num;
ptr = buf;
while (n > 0) {
/* 开始写*/ 
     if ((res = write (fd, ptr, n)) <= 0) {
      if (errno == EINTR)
       res = 0;
      else
       return (-1);
     }


     ptr += res;/* 从剩下的地方继续写     */ 
     n -= res;
}


return (num);
}
 
  
/* include readline */

static int	read_cnt;
static char	*read_ptr;
static char	read_buf[MAXLINE];

static ssize_t
my_read(int fd, char *ptr)
{

	if (read_cnt <= 0) {
again:
		if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {		if (errno == EINTR)
				goto again;
			return(-1);
		} else if (read_cnt == 0)
			return(0);
		read_ptr = read_buf;
	}

	read_cnt--;
	*ptr = *read_ptr++;
	return(1);
}

ssize_t
readline(int fd, void *vptr, size_t maxlen)
{
	ssize_t	n, rc;
	char	c, *ptr;

	ptr = vptr;
	for (n = 1; n < maxlen; n++) {
		if ( (rc = my_read(fd, &c)) == 1) {
			*ptr++ = c;
			if (c == '\n')
				break;	/* newline is stored, like fgets() */
		} else if (rc == 0) {
			*ptr = 0;
			return(n - 1);	/* EOF, n - 1 bytes were read */
		} else
			return(-1);		/* error, errno set by read() */
	}

	*ptr = 0;	/* null terminate like fgets() */
	return(n);
}

ssize_t
readlinebuf(void **vptrptr)
{
	if (read_cnt)
		*vptrptr = read_ptr;
	return(read_cnt);
}
/* end readline */

ssize_t
Readline(int fd, void *ptr, size_t maxlen)
{
	ssize_t		n;

	if ( (n = readline(fd, ptr, maxlen)) < 0)
		err_sys("readline error");
	return(n);
}
 
  
 
  
 
  
 
  
 
  
[1]UNIX网络编程卷1:53