示例消息C结构：

struct Registration
{
char multicastGroup[24];
pid_t clientPid;
};

用于序列化struct的客户端代码段

struct Registration regn ;
regn.clientPid = getpid();
strcpy(regn.multicastGroup,"226.1.1.1");

printf("PID:%d\n",regn.clientPid);        
printf("MG:%s\n",regn.multicastGroup);
printf("Size:%d\n",sizeof(regn));           //Size is 28

data = (unsigned char*)malloc(sizeof(regn));
memcpy(data,&regn,sizeof(regn));
printf("Size:%d\n",sizeof(data));           //Size is 4.

用于反序列化数据的服务器代码

if(recvfrom(sd,recvBuf,recvBufSize,(struct sockaddr*)&clientAddr,&len) < 0)
{
       printf("Error receiving message from client\n");
}
else
{
       printf("Message received:%s\n",recvBuf);
       printf("Size :%d\n",strlen(recvBuf));
       memcpy(&regn,sizeof(regn));
       printf("PID:%d\n",regn.clientPid);
       printf("MG:%s\n",regn.multicastGroup);
}

将结构复制到unsigned char *后,数组的大小仅为4.
为什么数据没有完全复制到数组？

服务器无法从char数组重构结构.
请让我知道我做错了什么.