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 = ;           //read函数读到的字节数
    unsigned char   *ptr = (char *)vptr; //指向缓冲区的指针
 
    while (nleft > )
    {
        nread = read(fd, ptr, nleft);
        if (- == nread)
        {
            if (EINTR == errno)
                nread = ;
            else
                return -;
        }
        else if ( == 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：

 int writen(int fd, const void *vptr, size_t n)
 {
     size_t          nleft = n;  //writen函数还需要写的字节数
     ssize_t         nwrite = ; //write函数本次向fd写的字节数
     const char*     ptr = vptr; //指向缓冲区的指针
 
     while (nleft > )
     {
         if ((nwrite = write(fd, ptr, nleft)) <= )
         {
             if (nwrite <  && EINTR == errno)
                 nwrite = ;
             else
                 return -;
         }
         nleft -= nwrite;
         ptr += nwrite;
     }
     return n;
 }

readline函数功能：读到'\n'或者读满缓冲区才返回

readline函数实现：

 static ssize_t readch(int fd, char *ptr)
 {
     static int          count = ;
     static char*        read_ptr = ;
     static char         read_buf[*] = {};
 
     if (count <= )
     {
     again:
         count = read(fd, read_buf, sizeof(read_buf));
         if (- == count)
             if (EINTR == errno)
                 goto again;
             else
                 return -;
         else if ( == count)
             return ;
         read_ptr = read_buf;
     }
     count--;
     *ptr = *read_ptr++;
     return ;
 }
 
 ssize_t readline(int fd, void *vptr, size_t maxlen)
 {
     ssize_t         i = ;
     ssize_t         ret = ;
     char            ch = '\0';
     char*           ptr = NULL;
 
     ptr = (char *)vptr;
 
     for (i = ; i < maxlen; ++i)
     {
         ret = readch(fd, &ch);
         if ( == ret)
         {
             *ptr++ = ch;
             if ('\n' == ch)
                 break;
         }
         else if ( == ret)
         {
             *ptr = ;
             return i-;
         }
         else
             return -;
     }
     *ptr = ;
     return i;
 }