unix网络编程readn,writen,readline包裹函数

一、Readn包裹函数

/* include readn */

#include "unp.h"
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);

}

二、Writen包裹函数

/* include writen */
#include "unp.h"

ssize_t /* Write "n" bytes to a descriptor. */
writen(int fd, const void *vptr, size_t n)
{
size_t nleft;
ssize_t nwritten;
const char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
if (nwritten < 0 && errno == EINTR)
nwritten = 0; /* and call write() again */
else
return(-1); /* error */
}
nleft -= nwritten;
ptr   += nwritten;
}
return(n);
}
/* end writen */
void
Writen(int fd, void *ptr, size_t nbytes)
{
if (writen(fd, ptr, nbytes) != nbytes)
err_sys("writen error");
}

三.Readline包裹函数

static int read_cnt;//刚开始可以置为一个负值（我的理解）
static char *read_ptr;
static char read_buf[MAXLINE];
static ssize_t
my_read(int fd, char *ptr)//每次最多读取MAXLINE个字符，调用一次，每次只返回一个字符
{
if (read_cnt <= 0) {
again:
if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {//如果读取成功，返回read_cnt=读取的字符if (errno == EINTR)
goto again;
return(-1);
} else if (read_cnt == 0)
return(0);
read_ptr = read_buf;
}
read_cnt--;//每次递减1，直到<0读完，才执行上面if的命令。
*ptr = *read_ptr++;//每次读取一个字符，转移一个字符
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);
}