根據代碼來看很容易理解，下面就是實際的代碼。
變長結構體的核心思想就是在結構體的最后一個數據結構為一個指針，這個指針指向的是這個結構體的末尾數據數組的首地址。

#include <stdlib.h>

typedef struct stru_zmq_server_msg
{
    int deviceId;
    int msgCode;
}TS_ZMQ_SERVER_MSG;

typedef struct stru_tcp_server_msg
{
    int msgLength;
    int msgBodyLen;
    TS_ZMQ_SERVER_MSG zmqMsgBody[1];
}TS_TCP_SERVER_MSG;


int main()
{
    int len = sizeof(TS_TCP_SERVER_MSG) + sizeof(TS_ZMQ_SERVER_MSG) * 2;
    TS_TCP_SERVER_MSG* tdata = (TS_TCP_SERVER_MSG*)malloc(len);
    tdata->msgLength = len;
    tdata->msgBodyLen = 2;
    TS_ZMQ_SERVER_MSG* data = (TS_ZMQ_SERVER_MSG*)tdata->zmqMsgBody;

    data[0].deviceId = 100;
    data[0].msgCode = 1;
    data[1].deviceId = 101;
    data[1].msgCode = 2;
    free(tdata);
    return 0;
}

轉載文章
https://www.cnblogs.com/dangerman/archive/2012/12/16/2820825.html