C++ UDP客户端未正确形成数据包

我正在尝试在Linux中创建一个客户端，以允许发送UDP数据包。到目前为止，程序似乎正确地组成了所有部分，但当我尝试发送数据时，程序无法发送数据包

，代码的示例输出如下所示：

jeremiah@ubuntu:~/Documents/Networking 2/Lab3/client$ sudo ./a.out 192.168.1.128 22222 great success Imperial Soviet Comrade: SVN -> sin_family: 2 Imperial Soviet Comrade: SVN -> sin_port: 52822 Imperial Soviet Comrade: SVN -> sin_addr: -2147374912 Attention Comrade: Enter Message: red Imperial Soviet Comrade: Data in packet dump ::::::::::::::::::::::::::::::::::::::::: start Imperial Soviet Comrade: the size of the UPC is 1576 Imperial Soviet Comrade: Socket: 3 Imperial Soviet Comrade: UPC -> flags: 1 Imperial Soviet Comrade: UPC -> offset: 0 Imperial Soviet Comrade: UPC -> length: 8 Imperial Soviet Comrade: UPC -> filename: red Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 00000000000000000000000000000000000000000000000000000000000000000000000000000000 Imperial Soviet Comrade: UPC -> data: 0000000000000000000000000000000000000000 Imperial Soviet Comrade: sizeof(UPC): 8 Imperial Soviet Comrade: sockaddr.sin_family: 2 Imperial Soviet Comrade: sockaddr.sin_port: 52822 Imperial Soviet Comrade: sockaddr.sin_addr.s_addr: -2147374912 Imperial Soviet Comrade: sizeof(sockaddr): 8 Imperial Soviet Comrade: Data in packet dump ::::::::::::::::::::::::::::::::::::::::::: end Imperial Soviet Comrade: size_sent: -1 Alert Comrade: Data not sent: Invalid argument jeremiah@ubuntu：~/Documents/Networking 2/Lab3/client$sudo./a.out 192.168.1.128 22222 巨大成功 帝国苏维埃同志：SVN->sin_家族：2 帝国苏维埃同志：SVN->sin\u港口：52822 帝国苏维埃同志：SVN->sin_地址：-2147374912 同志们注意：输入信息：红色 帝国苏维埃同志：数据包转储中的数据： 帝国苏维埃同志：UPC的规模是1576 苏维埃帝国同志：套接字：3 帝国苏维埃同志：UPC->旗帜：1 帝国苏维埃同志：UPC->偏移量：0 帝国苏维埃同志：UPC->长度：8 帝国苏维埃同志：UPC->filename:red 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：00000000000000000000000000000000000000000000000000000000 帝国苏维埃同志：UPC->数据：0000000000000000000000000000 苏维埃帝国同志：西泽夫（UPC）：8 苏维埃帝国同志：sockaddr.sin_家族：2 帝国苏维埃同志：sockaddr.sinu港口：52822 帝国苏维埃同志：sockaddr.sin_addr.s_addr:-2147374912 帝国苏维埃同志：西泽夫（索卡德尔）：8 帝国苏维埃同志：数据包转储中的数据： 帝国苏维埃同志：尺寸：1 警告同志：数据未发送：参数无效

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它完全编译无误，但printf函数中有来自casts的警告。如果能提供任何帮助，我们将不胜感激。

这确实令人怀疑：

int size_sent = sendto(SOCKET, UPC, sizeof(UPC)+2*MAX_MESSAGE, 0, 
                       (struct sockaddr*) &TARGET, sizeof(TARGET)+2*MAX_MESSAGE);

为什么要将2*MAX_消息添加到sockaddr结构的消息长度和大小中？ 最后一个很可能是您的

sendto（）

调用返回-1的原因

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还要记住，sizeof（UPC）将是4或8，而不是您想要的大小。

sendto（SOCKET，UPC，sizeof（UPC）+2*MAX_MESSAGE，0，（struct sockaddr*）

——当您真的想要发送一个3字节的数据报时，为什么要发送一个2803字节的数据报呢？这浪费了带宽，保证了任何“正常”情况下的IP碎片化链接，内核可能会选择扔掉这样的数据包（这可能是它不工作的原因）。还要注意的是，

select

与

recvfrom

结合使用有点傻。你可以只阻塞

recvfrom

，这样效率更高，效果也一样（顺便说一句，你也只收到你发送的一半--

recvfrom（SOCKET，buffer，MAX_MESSAGE，…）

）我真的有这些，因为我不确定它是否发送了我需要的大小。我确实删除了这两个，并且得到了完全相同的响应。这是因为sizeof（TARGET）也是错误的。目标是指针，而不是它所指向的结构。请注意，这也会使&TARGET错误。您希望发送到（…，TARGET，sizeof（struct sockaddr_in））；相反，您缺少了一个非常非常基本的C/C++概念——某个东西的大小与它包含的内容无关，只与它的类型有关。如果您对指针执行

sizeof

操作，您将得到该指针的大小。