网络数据传输过程中接收到的缓冲区的访问冲突错误 [英] access violation error of a received buffer during network transfer of data

问题描述

我正在构建2个应用程序(服务器和客户端)，其中，在接受客户端连接后，服务器立即通过缓冲区发送数据库中存在的信息.虽然客户端收到了缓冲区，但是当我尝试访问缓冲区时，会显示访问冲突错误.

我在这里粘贴代码的发送和接收逻辑:

发送逻辑:

I am building 2 applications(a server & a client) where in, immediately after a client connection is accepted, the server send information present in the database through a buffer. Although the client receives the buffer, but when I am trying to access the buffer, an access violation error is shown.

I am pasting the sending and receiving logic of my code here:

sending logic:

if(LOWORD(lParam)==FD_ACCEPT)
    {
        BOOL b = m_ServerSocket.Accept(*m_pClientSocket);
        if(b==FALSE)
        {
            AfxMessageBox("Unable to accept client's connection");
        }
        else
        {
            AfxMessageBox("Client Connected");
            //send the database info immediately after accepting the clients connection.....
            m_database.Open("AVIFilesDSN");   //database object connecting to DSN
            CAVIFileRecordset* pAviFileRecordset; //pointer to the derived class of CRecordset.
            pAviFileRecordset = new CAVIFileRecordset(&m_database);
            pAviFileRecordset->Open();
            pstrArray = new CStringArray;  //pointer to CStringArray
            while(!pAviFileRecordset->IsEOF())
            {
                //m_FilePath variable(CString) pointing to a field in database table(containing filepaths),
                pstrArray->Add(pAviFileRecordset->m_FilePath);
                pAviFileRecordset->MoveNext();
            }            
            pAviFileRecordset->Close();
            delete pAviFileRecordset;
            m_pClientSocket->Send((void*)pstrArray,MAX_BUFFER_SIZE);
            //delete pstrArray;
        }

接收逻辑:

receiving logic:

int done;
char* pBuffer[MAX_BUFFER_SIZE];  //MAX_BUFFER_SIZE = 4096
pBuffer[MAX_BUFFER_SIZE] = new char;
CStringArray* pStrArray;
pStrArray = new CStringArray;
if(LOWORD(lParam)==FD_READ)
{
done = m_CSoc.Receive((void*)pBuffer,MAX_BUFFER_SIZE);
if(done==SOCKET_ERROR)
{
    AfxMessageBox("recv failed");
    return;
}
//receiving the database info
pStrArray = (CStringArray*)pBuffer;
nTemp1 = pStrArray->GetUpperBound();
nTemp = 0;
while(nTemp<=nTemp1)
{
         //displaying the contents of the string array on a list control
         m_FileListCtrl.InsertItem(nTemp,pStrArray->GetAt(nTemp)); //error occurring here
     nTemp++;
}
AfxMessageBox("Updated Files List");

}

我可以仅将CStringArray指针作为Receive函数中的第一个参数传递.使用CStringArray *转换接收到的缓冲区后，我可以看到数组上的元素数量和数据库中的项目数量相同.但是，当我尝试在列表控件上显示接收到的信息时，我收到了访问冲突错误.

Can I just pass the CStringArray pointer as the 1st argument in the Receive function. After casting the received buffer with CStringArray* I am able to see that the number of elements on the array and the number of items in the database are same. But when I am trying to show the received information on a list control, I am receiving the access violation error.

推荐答案

您不能使用动态分配的对象发送对象通过网络连接的内存.您必须通过访问缓冲区来发送数据并获取它们的实际大小，使用本地缓冲区接收它们，并将接收到的数据复制到新对象.

在您的情况下，您可以在发送方上分配一个缓冲区，将所有带有NULL终止符的字符串复制到此缓冲区，然后发送.在接收端，提取以NULL结尾的字符串，并将每个字符串附加到CString对象.但是，这需要一些其他代码来处理可变长度或使用缓冲区，该缓冲区可以容纳所有可能的字符串(最大字符串数乘以最大字符串长度再加上一个).

You can''t send objects using dynamically allocated memory over a network connection. You must send the data by accessing the buffers and get their actual size, receive them using a local buffer, and copy the received data to a new object.

In your case, you may allocate a buffer on the sender, copy all strings with NULL terminators to this buffer, and send it. On the receive side, extract the NULL terminated strings and append each to a CString object. However, this requires some additional code to handle the variable length or usage of a buffer that can hold all possible strings (max. number of strings multiplied by max. string length plus one).

在接收器端，该行

On the receiver side, the line

pBuffer[MAX_BUFFER_SIZE] = new char;

错误有两个原因:(a)它在无效位置访问数组(可用的最高索引为MAX_BUFFER_SIZE -1)，(b)"new char"分配一个"char"对象，该对象创建一个内存泄漏，完全没有必要.这不是C#:-)

如果要使用NULL字符初始化缓冲区的最后一个单元格，请使用

is wrong for two reasons: (a) It accesses the array at an invalid position (the highest index available is MAX_BUFFER_SIZE -1 ), (b) ''new char'' allocates a ''char'' object, which creates a memory leak and is totally unnecessary. This is not C# :-)

If you want to initialize the last cell of your buffer with a NULL character, then use

pBuffer[MAX_BUFFER_SIZE-1] = 0;

下一个错误是当您将缓冲区转换为CStringArray时:

The next error is when you cast your buffer into a CStringArray:

pStrArray = (CStringArray*)pBuffer;

您将必须解析缓冲区，并一一分配字符串数组的元素.简单地将char *转换为CStringArray *是行不通的.

You will have to parse your buffer and assign the elements of your string array one-by-one. Simply casting a char* into a CStringArray* doesn''t work.

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