1、warning: no newline at end of file
在文件最后一行加上回车键
解释：在《Rationale for the C99 standard》一文中，有C99的相关信息：
A backslash immediately before a newline has long been used to continue string literals, as well as preprocessing command lines. In the interest of easing machine generation of C, and of transporting code to machines with restrictive physical line lengths, the C89 Committee generalized this mechanism to permit any token to be continued by interposing a backslash/newline sequence.
c/c++代码的每一行后面有一个“结束符”，也就是newline。避免当被include的文件展开后，前一个文件的最后一行与后一个文件的第一行直接被连接成一行从而造成错误。
2、warning: comparison between pointer and integer
解释：integer与pointer比较
3、 warning: assignment discards qualifiers from pointer target type
解释：赋值时，取消了右值的限定。
4、 warning: passing argument 1 of 'send' makes pointer from integer without a cast
解释：函数send的第一个integer型参数没有强制转换为pointer型
5、warning: comparison is always true due to limited range of data type
解释：由于数据类型范围的限制，比较结果一直为真。
6、warning: initialization from incompatible pointer type
解释：不兼容指针类型的初始化
7、 warning: return makes pointer from integer without a cast
解释：return使integer转换为pointer，没有加强制类型转换。
8、warning: incompatible implicit declaration of built-in function 'printf'
解释：与内置的printf函数隐士声明不兼容。
11、warning: assignment from incompatible pointer type
13、warning: "protocol_type" redefined