将缓冲区复制到结构时缺少数据

我有一个接收 16 字节请求消息的 TCP 服务器套接字。请求消息将有几个字段，根据字段值，我需要继续执行不同的操作。

当我尝试将缓冲区复制到结构时，我可以看到丢失的数据。我尝试了所有可能的方法，但无法弄清楚我是否需要进行结构填充。

我的结构看起来像，

struct stRequestMsg {
    uint16_t startTag;
    uint32_t messageSize;
    uint16_t messageID;
    uint16_t sequenceNumber;
    uint16_t messageType;
    uint32_t reserved;
};

我所做的只是，

char buff[1024]
result = static_cast<int>(recv(sockDesc, buff, sizeof(stRequestMsg), 0));
    if (0 < result) {
        printf("n Actual value on buffer");
        for (int i = 0; i < result; i++)
        {
            printf("n buff[%d] = 0x%x", i,buff[i]);
        }
        reqMessage = *(stRequestMsg *)buff;
        printf("n RESULT of reqMessage = *(stRequestMsg *)buff;");
        printf("nstartTag : 0x%x", reqMessage.startTag);
    printf("nmessageSize : 0x%x", reqMessage.messageSize);
    printf("nmessageID : 0x%x", reqMessage.messageID);
    printf("nsequenceNumber : 0x%x", reqMessage.sequenceNumber);
    printf("nmessageType : 0x%x", reqMessage.messageType);
printf("nreserved : 0x%x", reqMessage.reserved);
        stRequestMsg hdr;
        std::copy(&hdr, &hdr + 1, reinterpret_cast<stRequestMsg*>(buff));
        printf("n RESULT of std::copy(&hdr, &hdr + 1, reinterpret_cast<stRequestMsg*>(buff));");
        printf("nstartTag : 0x%x", reqMessage.startTag);
    printf("nmessageSize : 0x%x", reqMessage.messageSize);
    printf("nmessageID : 0x%x", reqMessage.messageID);
    printf("nsequenceNumber : 0x%x", reqMessage.sequenceNumber);
    printf("nmessageType : 0x%x", reqMessage.messageType);
printf("nreserved : 0x%x", reqMessage.reserved);
        memcpy(&reqMessage, buff, sizeof(stRequestMsg));
        printf("n RESULT of std::copy(&hdr, &hdr + 1, reinterpret_cast<stRequestMsg*>(buff));");
        printf("nstartTag : 0x%x", reqMessage.startTag);
    printf("nmessageSize : 0x%x", reqMessage.messageSize);
    printf("nmessageID : 0x%x", reqMessage.messageID);
    printf("nsequenceNumber : 0x%x", reqMessage.sequenceNumber);
    printf("nmessageType : 0x%x", reqMessage.messageType);
printf("nreserved : 0x%x", reqMessage.reserved);
        reqMessage = *reinterpret_cast<stRequestMsg*>(buff);
        printf("n RESULT of reqMessage = *reinterpret_cast<stRequestMsg*>(buff);");
        printf("nstartTag : 0x%x", reqMessage.startTag);
    printf("nmessageSize : 0x%x", reqMessage.messageSize);
    printf("nmessageID : 0x%x", reqMessage.messageID);
    printf("nsequenceNumber : 0x%x", reqMessage.sequenceNumber);
    printf("nmessageType : 0x%x", reqMessage.messageType);
printf("nreserved : 0x%x", reqMessage.reserved);
    }

我可以看到buff上收到的值是正确的，但是当我尝试将整个缓冲区映射到结构时，我可以看到丢失的数据。我相信解决方案可能很简单，但我不知道问题出在哪里。

输出如下所示，

Actual value on buffer
 buff[0] = 0x50
 buff[1] = 0x0
 buff[2] = 0x1e
 buff[3] = 0x0
 buff[4] = 0x0
 buff[5] = 0x0
 buff[6] = 0x31
 buff[7] = 0x0
 buff[8] = 0x1
 buff[9] = 0x0
 buff[10] = 0x2
 buff[11] = 0x0
 buff[12] = 0x1
 buff[13] = 0x0
 buff[14] = 0x0
 buff[15] = 0x0
RESULT of reqMessage = *(stRequestMsg *)buff;
startTag : 0x50
messageSize : 0x310000
messageID : 0x1
sequenceNumber : 0x2
messageType : 0x1
reserved : 0x8a5c6da
RESULT of std::copy(&hdr, &hdr + 1, reinterpret_cast<stRequestMsg*>(buff));
startTag : 0x50
messageSize : 0x310000
messageID : 0x1
sequenceNumber : 0x2
messageType : 0x1
reserved : 0x8a5c6da
RESULT of memcpy(&reqMessage, buff, sizeof(stRequestMsg));
startTag : 0xf7ec
messageSize : 0x1e0050
messageID : 0x0
sequenceNumber : 0x31
messageType : 0x1
reserved : 0x1
RESULT of reqMessage = *reinterpret_cast<stRequestMsg*>(buff);
startTag : 0xf7ec
messageSize : 0x1e0050
messageID : 0x0
sequenceNumber : 0x31
messageType : 0x1
reserved : 0x1

但我所期望的是

startTag = 0x5000;
messageSize = 0x1E000000;
messageID = 0x3100;
sequenceNumber = 0x100;
messageType = 0x200;
reserved = 0x1000000;

编辑：我尝试更改消息大小的可变大小，并保留为uint16_t，通过这样做memcpy我收到了所有正确的信息。