It seems that when I have one mysql_real_query() function in a continuous while loop, the query will get executed OK.

However, if multiple mysql_real_query() are inside the while loop, one right after the other. Depending on the query, sometimes neither the first query nor second query will execute properly.

This seems like a threading issue to me. I'm wondering if the mysql c api has a way of dealing with this? Does anyone know how to deal with this? mysql_free_result() doesn't work since I am not even storing the results.

//keep polling as long as stop character '-' is not read
while(szRxChar != '-')
{
    // Check if a read is outstanding
    if (HasOverlappedIoCompleted(&ovRead))
    {
        // Issue a serial port read
        if (!ReadFile(hSerial,&szRxChar,1,
                &dwBytesRead,&ovRead))
        {
            DWORD dwErr = GetLastError();
            if (dwErr!=ERROR_IO_PENDING)
                return dwErr;
        }
    }

    // Wait 5 seconds for serial input
    if (!(HasOverlappedIoCompleted(&ovRead)))
    {
        WaitForSingleObject(hReadEvent,RESET_TIME);
    }

    // Check if serial input has arrived
    if (GetOverlappedResult(hSerial,&ovRead,
            &dwBytesRead,FALSE))
    {
        // Wait for the write
        GetOverlappedResult(hSerial,&ovWrite,
            &dwBytesWritten,TRUE);

        //load tagBuffer with byte stream
        tagBuffer[i] = szRxChar;
        i++;
        tagBuffer[i] = 0; //char arrays are \0 terminated

        //run query with tagBuffer
        if( strlen(tagBuffer)==PACKET_LENGTH )
        {
            sprintf(query,"insert into scan (rfidnum) values ('");
            strcat(query, tagBuffer);
            strcat(query, "')");
            mysql_real_query(&mysql,query,(unsigned int)strlen(query));

            i=0;
        }

        mysql_real_query(&mysql,"insert into scan (rfidnum) values ('2nd query')",(unsigned int)strlen("insert into scan (rfid) values ('2nd query')"));

        mysql_free_result(res);
    }
}