? Strange print behaviour

[Richard Ellis]

Firstly thanks to all who maintain and contribute to this site. I have learnt a lot from your efforts, so thanks again. Now to my problem. I have an application that is required to print some reports. I have done this by deriving a view from CView and using the MFC framework to do the printing for me. I have overwritten OnPreparePrinting, OnPrepareDC, OnBeginPrinting etc. Now everything has been working fine for quite a while now. Yesterday I came to do some minor modifications to the format of the report. I recompiled my application in debug and stepped into my code. I got an assertion failure in ...\mfc\src\viewprnt.cpp. It occurs in the function DoPreparePrinting(). pInfo has been created using default values etc - I don't try and do anything with it. I won't copy all the code for the function in here but basically it is an if..else statement. My code executes the else statement and I have marked the bit that fails. else { // otherwise, bring up the print dialog and allow user to change things // preset From-To range same as Min-Max range pInfo->m_pPD->m_pd.nFromPage = (WORD)pInfo->GetMinPage(); pInfo->m_pPD->m_pd.nToPage = (WORD)pInfo->GetMaxPage(); if (pApp->DoPrintDialog(pInfo->m_pPD) != IDOK) return FALSE; // do not print } ASSERT(pInfo->m_pPD != NULL); ***** ASSERT(pInfo->m_pPD->m_pd.hDC != NULL); **** This fails if (pInfo->m_pPD->m_pd.hDC == NULL) return FALSE; Now the things that bother me are that it worked in the past but not now. I have not changed the code that produces the report - only a small cosmetic change the the layout of the report. And further if I execute the program rather than step into it it works! I have done my best to wade through the documentation hand have searched the MSDN site and read the references I could find. I have stepped through this repeatedly and am most puzzled. From looking at the code in CView I can see that pInfo->m_pPD->m_pd.hDC seems to be created when CreatePrinterDC is called. However as I step through that statement is never called - it is in branches of code that my application doesn't execute. I don't really want to change what the user sees because I do want them to be able to change the default printer used. I have tried cutting and pasting CView's DoPreparePrinting function and inserting a CreatePrinterDC call but all this leads to is a crash when CView later on calls GetPortName because the pointer returned by ::GlobalLock(hDevnames) is NULL. If anyone has any ideas as to what might have happened