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Errata

Errors always pop up where you least expect them. This page describes errors contained in the book.
  

Page 78 - Attempting to call SysFreeString() with an unset pointer.

Thanks to Tomas Palmer for pointing this out. Here is a code snippet identifying the problem.
BOOL MyCheckingAccount::Init(const CString& name,
                             const CString& serverName,
                             CString& errmsg)
{
    Reset();

    // Create server info.
    COSERVERINFO  serverInfo;
    COSERVERINFO* pServerInfo;
    if ( serverName.IsEmpty() )
    {
        // Use local server.
        pServerInfo = NULL;
    }
    else
    {
        serverInfo.dwReserved1 = 0;
        serverInfo.dwReserved2 = 0;
        serverInfo.pwszName    = serverName.AllocSysString();
        serverInfo.pAuthInfo   = NULL;
        pServerInfo = &serverInfo;
    }

    // Create MULTI_QI array to get all pertinent interfaces.
    MULTI_QI mqi[] =
    {
        {&IID_IAccount,         NULL, 0},
        {&IID_IAccountInit,     NULL, 0},
        {&IID_ICheckingAccount, NULL, 0},
    };

    // Create a server object instance.
    HRESULT hr;
    hr = CoCreateInstanceEx
            (CLSID_Ch3CheckingAccount, NULL,
             CLSCTX_LOCAL_SERVER | CLSCTX_REMOTE_SERVER,
             pServerInfo, 3, mqi);

    ::SysFreeString(serverInfo.pwszName);   // ****** ERROR ******
Notice that if the serverName argument to Init() is an empty string, serverInfo.pwszName never gets set. To correct the problem, a check needs to be made before calling ::SysFreeString(). For example, the check could be written as shown here:
    if ( !serverName.IsEmpty() )
    {
        ::SysFreeString(serverInfo.pwszName);
    }

 

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Last modified: August 12, 2003