Linux网络编程-readn函数、writen函数、readline函数实现

readn函数功能：在网络编程的读取数据中，通常会需要用到一个读指定字节才返回的函数，linux系统调用中没有给出，需要自己封装。

readn实现代码：

int readn(int fd, void *vptr, size_t n)
{
    size_t          nleft = n;           //readn函数还需要读的字节数
    ssize_t         nread = 0;           //read函数读到的字节数
    unsigned char   *ptr = (char *)vptr; //指向缓冲区的指针

    while (nleft > 0)
    {
        nread = read(fd, ptr, nleft);
        if (-1 == nread)
        {
            if (EINTR == errno)
                nread = 0;
            else
                return -1;
        }
        else if (0 == nread)
        {
            break;
        }
        nleft -= nread;
        ptr += nread;
    }
    return n - nleft;
}

 

 

writen函数功能：读满n个字节才返回

writen代码实现：

 1 int writen(int fd, const void *vptr, size_t n)
 2 {
 3     size_t          nleft = n;  //writen函数还需要写的字节数
 4     ssize_t         nwrite = 0; //write函数本次向fd写的字节数
 5     const char*     ptr = vptr; //指向缓冲区的指针
 6 
 7     while (nleft > 0)
 8     {
 9         if ((nwrite = write(fd, ptr, nleft)) <= 0)
10         {
11             if (nwrite < 0 && EINTR == errno)
12                 nwrite = 0;
13             else
14                 return -1;
15         }
16         nleft -= nwrite;
17         ptr += nwrite;
18     }
19     return n;
20 }

 

 

readline函数功能：读到'\n'或者读满缓冲区才返回

readline函数实现：

 1 static ssize_t readch(int fd, char *ptr)
 2 {
 3     static int          count = 0;
 4     static char*        read_ptr = 0;
 5     static char         read_buf[1024*4] = {0};
 6 
 7     if (count <= 0)
 8     {
 9     again:
10         count = read(fd, read_buf, sizeof(read_buf));
11         if (-1 == count)
12             if (EINTR == errno)
13                 goto again;
14             else
15                 return -1;
16         else if (0 == count)
17             return 0;
18         read_ptr = read_buf;
19     }
20     count--;
21     *ptr = *read_ptr++;
22     return 1;
23 }
24 
25 ssize_t readline(int fd, void *vptr, size_t maxlen)
26 {
27     ssize_t         i = 0;
28     ssize_t         ret = 0;
29     char            ch = '\0';
30     char*           ptr = NULL;
31 
32     ptr = (char *)vptr;
33 
34     for (i = 1; i < maxlen; ++i)
35     {
36         ret = readch(fd, &ch);
37         if (1 == ret)
38         {
39             *ptr++ = ch;
40             if ('\n' == ch)
41                 break;
42         }
43         else if (0 == ret)
44         {
45             *ptr = 0;
46             return i-1;
47         }
48         else
49             return -1;
50     }
51     *ptr = 0;
52     return i;
53 }

 

posted on 2016-12-08 16:43  yqzheng  阅读(2503)  评论(0)  编辑  收藏  举报

导航