Invalid Pointer Operation - Delphi XE

Question

I can\'t seem to figure this one out. My program compiles and runs successfully, but during debugging only it pops up a message box saying \"Invalid Pointer Operation\" when

Answer 1

Invalid pointer operations occur when you tell the Delphi memory manager to release memory that doesn't belong to it. There are three ways that might happen:

• Freeing a pointer or object that has already been freed.
• Using FreeMem to free something that was allocated by some other memory manager (such as GlobalAlloc or CoTaskMemAlloc).
• Freeing an uninitialized pointer. (This is distinct from freeing a null pointer, which is completely safe.)

Somewhere in your program, you are doing one of those things. The debugger has detected the exception thrown by the memory manager, so do some debugging. From the stack trace, you should be able to see which variable you're trying to free. Check the rest of your program for other ways that variable is used.

Tools like MadExcept and Eureka Log can help you find double-free errors. They can keep track of where the pointer in question got allocated and where it was freed the first time, and that is sometimes enough information to figure out your mistake and stop freeing things multiple times.

Answer 2

I have been caught out by this type of "indicated error" during Delphi debugging.

Check if you have any watched variables with "Allow Function Calls" enabled or watches that try to show other variables in the same unit (or global) that might be uninitialised. When stopping on a breakpoint this can cause Delphi's debugger to attempt to display the value via a function call that accesses an uninitialised Pointer or variable. The actual variable that causes the AV my not even be on your watch list.

Answer 3

A 4th reason an invalid pointer operation can occur. I had two pointers that where array[0..1000] of real and a third pointer that was an array[1..200] of real. All 3 pointers where initialized with for i := 0 to 1000 do begin ptr1^[i]:=0;ptr2^[i]:=0;ptr3^[i]:=0; end; While this poor programing did not bother Pascal in Delphi a call to Dispose any of the 3 pointers resulted in an Invalid Pointer Operation. The fix was simply to initialize the 3rd pointer correctly.

Answer 4

An Invalid Pointer exception is thrown by the memory manager when it tries to free invalid memory. There are three ways this can happen.

The most common is because you're trying to free an object that you've already freed. If you turn on FastMM's FullDebugMode, it will detect this and point you directly to the problem. (But make sure to build a map file so it will have the information it needs to create useful stack traces from.)

The second way is if you're trying to free memory that was allocated somewhere other than the memory manager. I've seen this a few times when passing a string from a Delphi EXE to a Delphi DLL that wasn't using the shared memory manager feature.

And the third way involves messing around with pointers directly and probably doesn't apply to you. If you try to FreeMem or Dispose a bad pointer that doesn't refer to an actual block of memory allocated by FastMM, you'll get this error.

It's most likely the first one. Use FullDebugMode and you'll find the source of the problem easily.