MSVC & MinGW
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Hello everyone,
I recently spend an ungodly amount of time searching for an memory access violation error that only accured when compiled with MSVC2015.
Turns out I forgot to set a Pointer back to
NULLafter deleting the object ... Silly me.Somehow this was not a problem with MinGW. Does the MinGW compiler automatically set the Pointer to NULL if you call
deleteLater()? That would explain a lot.
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Q: What does it do?
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Hello everyone,
I recently spend an ungodly amount of time searching for an memory access violation error that only accured when compiled with MSVC2015.
Turns out I forgot to set a Pointer back to
NULLafter deleting the object ... Silly me.Somehow this was not a problem with MinGW. Does the MinGW compiler automatically set the Pointer to NULL if you call
deleteLater()? That would explain a lot.No. Such behavior would violate C++ standard and cannot be expected from any reasonable compiler.
What you are probably seeing is use-after-free, which in case of MinGW somehow works because old memory hasn't been overwritten yet, and in case of MSVC it gets overwritten fast enough to reveal the bug
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Thanks for the clarification!
That is actually more in line with my original reasoning: "This is just happenstance." ;-)I'll mark it as sloved, thanks again.
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Hello everyone,
I recently spend an ungodly amount of time searching for an memory access violation error that only accured when compiled with MSVC2015.
Turns out I forgot to set a Pointer back to
NULLafter deleting the object ... Silly me.Somehow this was not a problem with MinGW. Does the MinGW compiler automatically set the Pointer to NULL if you call
deleteLater()? That would explain a lot.@J.Hilk said in MSVC & MinGW:
I recently spend an ungodly amount of time searching for an memory access violation error
A debugger would have found the source of the error fairly quickly.
- For MinGW, use GDB (already included in the copy of MinGW that's bundled with Qt).
- For MSVC, use CDB (installed separately)
If you're working on a *nix machine, Valgrind is a tool designed specifically to detect memory errors like this.
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@J.Hilk said in MSVC & MinGW:
I recently spend an ungodly amount of time searching for an memory access violation error
A debugger would have found the source of the error fairly quickly.
- For MinGW, use GDB (already included in the copy of MinGW that's bundled with Qt).
- For MSVC, use CDB (installed separately)
If you're working on a *nix machine, Valgrind is a tool designed specifically to detect memory errors like this.
@JKSH
I actually used a debugger, the problem was, my program was halted not on the right spot but at random places in my code.
I halted on*List.clear().List is a list of pointers andListitself is a class, member and allocated on the stack. So I checked everything that was connected to the list and the objects it pointed to.
The error itself that I later fixed was 10-20 lines above this entry...
Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct
Q: What's that?
A: It's blue light.
Q: What does it do?
A: It turns blue. -
@JKSH
I actually used a debugger, the problem was, my program was halted not on the right spot but at random places in my code.
I halted on*List.clear().List is a list of pointers andListitself is a class, member and allocated on the stack. So I checked everything that was connected to the list and the objects it pointed to.
The error itself that I later fixed was 10-20 lines above this entry...@J.Hilk said in MSVC & MinGW:
@JKSH
I actually used a debugger, the problem was, my program was halted not on the right spot but at random places in my code.
I halted on*List.clear().List is a list of pointers andListitself is a class, member and allocated on the stack. So I checked everything that was connected to the list and the objects it pointed to.
The error itself that I later fixed was 10-20 lines above this entry...Then a memory checker is our friend.
I mentioned Valgrind in my previous post. It's not available on Windows, but Dr. Memory looks promising: http://www.drmemory.org/ (I haven't used this myself, though)
