GetSaveFileName exception

This is a discussion on GetSaveFileName exception within the Windows Programming forums, part of the Platform Specific Boards category; I don't mean to annoy the readers, but I need some help with an exception problem with the function (I'm ...

  1. #1
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    GetSaveFileName exception

    I don't mean to annoy the readers, but I need some help with an exception problem with the function (I'm sure a lot of you have used this function, but I'm still inexperienced with it). Below is my code:

    Code:
    BOOL AskUser(IN HWND hDlg, 
    			 OUT PEXTDEVMODE pdevmode)
    {
    	OPENFILENAME fn;
    
    	// initialize OPENFILENAME structure
    	ZeroMemory(&fn, sizeof(fn));
    
    	fn.lStructSize = sizeof(OPENFILENAME);
    	fn.Flags = OFN_HIDEREADONLY;
    	fn.lpstrTitle = L"PDF SaveFile";
    	fn.hwndOwner = NULL;
    
    	// ???
    	fn.lpstrCustomFilter = NULL;
    	fn.nMaxCustFilter = 0;
    
    	// output format
    	fn.lpstrFilter = L"*.pdf";
    	fn.nFilterIndex = 0; //formatIdx+1;     // the index here is not zero-based
    
    	// output file name + path + ext
    	fn.lpstrFile = L"";
    	fn.nMaxFile = 1000;
    
    	// output file name + ext
    	fn.lpstrFileTitle = L"";
    	fn.nMaxFileTitle = 500;
    
    	// output folder
    	fn.lpstrInitialDir = NULL;
    
    	GetSaveFileName(&fn);
    
    	return TRUE;
    }
    I'm getting exception errors at run-time after I have pressed "OK" button on the Save File dialog box.
    Code:
    First-chance exception at 0x763b1ff8 (comdlg32.dll) in Savefile.exe: 0xC0000005: Access violation writing location 0x0041597c.
    Unhandled exception at 0x763b1ff8 (comdlg32.dll) in Savefile.exe: 0xC0000005: Access violation writing location 0x0041597c.
    After searching through the forum, there's a similar problem with an exception getting thrown (Troubles with GetOpenFileName()). However, I'm not sure 100% if this is the case. I'm not sure what is fundamentally wrong with how I've set up the openfilename structure as I have attempted to follow MSDN documentation as diligently as I could. The next step for me perhaps would be using a debugger such as windbg or Visual Studio debugger to look at the register values to get some clue about the exception, but I'm not sure how to make sense out of it. Any suggestions would be much appreciated. Thanks in advance.

  2. #2
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    I don't have much experience with OPENFILENAME either so I don't know how much help I will be, but where you have "output filename + path + ext" there is nothing for fn.lpstrFile. Do you need a valid path such as C:\ in order to save the file correctly?

  3. #3
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    No, I haven't included a filepath. I have the user specify the filepath, and the parameter being passed is acting both as an input and output.

  4. #4
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    No, I haven't included a filepath. I have the user specify the filepath, and the parameter being passed is acting both as an input and output.
    Yes, but that's exactly the problem:
    Code:
    	// output file name + path + ext
    	fn.lpstrFile = L"";
    	fn.nMaxFile = 1000;
    Now, nMaxFile:
    Quote Originally Posted by MSDN
    Specifies the size, in TCHARs, of the buffer pointed to by lpstrFile.
    First, you're passing a pointer to const memory (a string literal, which is const) that will be used as an output buffer. Then you tell windows that it has space for 1000 bytes. (It has space for exactly 1, and it's read-only.)

    You need to actually allocate memory, either in heap or stack, for lpstrFile, and pass the appropriate size of that memory to nMaxFile.
    Ditto for lpstrFileTitle, although this one is optional. Set it to NULL if you don't plan to use it.
    Finally, the string you are passing for lpstrFilter is incorrectly formatted. Read the documentation.
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  5. #5
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    Thanks for all your advices. After following your advices and rereading the documentation and more sample code, I have managed to achieve what I wanted to do to retrieve the filepath.

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