I get always an error "exception thrown: read access violation. Isf was nullptr."

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I use isf (type: IShellFolder* defined in ShlObjDl_Core.h) to use ParseDisplayName because it's a nonstatic member of IShellFolder, so it must be relative to a specific object.
But, when I use that code:

C++

IShellFolder* isf;
LPITEMIDLIST lprnt = { 0 };
ULONG lngth;
isf->ParseDisplayName(hWnd, NULL, (LPWSTR)"C:", &lngth, &lprnt, NULL);

I get:

Exception thrown: read access violation. isf was nullptr.

What I'm doing wrong?

What I have tried:

I've tried:
1- adding * to IShellFolder* to become IShellFolder** but it didn't work.

And this question isn't like the previous question (about a function getting a structure passed at one of its arguments) but it is about a reference from an variable for a function.

Posted 1-Apr-23 1:46am

Member 15925018

Updated 1-Apr-23 22:10pm

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Richard MacCutchan · Answer 1 · 2023-04-01T01:57:00

Similar to your previous question at I get always an error "exception thrown: write access violation. Lpsh was nullptr."[^]. But in this case you create a pointer but you do not initialise it to point to anything. If you do not understand pointers and references then go back to your C reference for guidance.
For an example of using the IShellFolder interface see Getting Information About the Contents of a Folder - Win32 apps | Microsoft Learn[^].

[edit]
Also the following is incorrect in the call to ParseDisplayName;

C++

(LPWSTR)"C:"

You cannot use a cast to convert an ASCII string to Unicode. You need to generate the Unicode characters at compile time by using the L prefix to the string, thus:

C++

L"C:"

[/edit]

KarstenK · Answer 2 · 2023-04-01T22:10:00

As Richard already wrote, you are missing some basics. To kickstart read the Microsoft documentation.

Such stuff isnt a walk in the park, so you must understand the complex topic. Good luck.

Here is some interesting stuff on github. When reading that well written article you get a taste about the complexity of COM.

additional tip: in C# the most of that boring stuff is handled under the hood.

I get always an error "exception thrown: read access violation. Isf was nullptr."

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I get always an error "exception thrown: read access violation. Isf was nullptr."

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