Free Allocated Memory Generates Exception - C++

There is a function in my application in which memory is allocated for formatting a port name. CreateFile is called to open the port. At the end of the function free is called to attempt to free the allocated memory.

DWORD CSerialPort::Open( wchar_t * port )
    DCB dcb = {0};
    void * pvThreadData = NULL;
    wchar_t * pwcPortName = NULL;

    /* Validate parameters. */

    pwcPortName = (wchar_t *)malloc( wcslen( port ) + 6 );

    if ( pwcPortName == NULL )
        TRACE(_T("CSerialPort::Open : Failed to allocate memory for formatted serial port name.\r\n\tError: %d\r\n\tFile: %s\r\n\tLine: %d\r\n"), ERROR_NOT_ENOUGH_MEMORY, __WFILE__, __LINE__);

    memcpy( pwcPortName, L"\\\\.\\", 4 * 2 );
    memcpy( pwcPortName + 4, port, wcslen( port ) * 2 + 2 );

    // Get a handle to the serial port.
    _hSerialPort = CreateFile(
        pwcPortName,                    // Formatted serial port
        GENERIC_READ | GENERIC_WRITE,   // Access: Read and write
        0,                              // Share: No sharing
        NULL,                           // Security: None
        OPEN_EXISTING,                  // OM port already exists
        FILE_FLAG_OVERLAPPED,           // Asynchronous I/O
        NULL                            // No template file for COM port

    if ( _hSerialPort == INVALID_HANDLE_VALUE )
        TRACE(_T("CSerialPort::Open : Failed to get the handle to the serial port.\r\n\tError: %d\r\n\tFile: %s\r\n\tLine: %d\r\n"), ::GetLastError(), __WFILE__, __LINE__);
        return ::GetLastError();

    /* Initialize the DCB structure with COM port parameters with BuildCommDCB. */

    /* Set the serial port communications events mask with SetCommMask. */

    /* Set serial port parameters with SetCommState. */

    /* Set the serial port communications timeouts with SetCommTimeouts. */

    /* Create thread to handle received data with CreateThread. */

    free( pwcPortName );                 // <-- Exception thrown here.

    return dwRetVal;

Can anyone tell me what I'm doing wrong? Thanks.


malloc allocates bytes, but you are using the allocated memory to store wchar_t.

You have to change the malloc size parameter to match your existing memcpy usage:

pwcPortName = (wchar_t *)malloc( wcslen( port ) + 6 );

should be

pwcPortName = (wchar_t *)malloc( (wcslen( port ) + 6) * sizeof(wchar_t));

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