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unable to delete Dll memory from an executable

Posted on 2008-06-18
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Last Modified: 2013-12-14
Hi,
Following is the situation:
I have a dynamic library which has a static method and creates and returns a pointer to the class  object.
I load this library from an executable, call the static method and try deleting the pointer. It complains with the following:
Debug assertion failed.
Expression: _CrtValidHeapPointer(pUserData)

I need to know why is this happening?
Please guide to me any relevant article which might be useful for understanding this topic.

cheers,
tushar.


// Header file for my library : mylib.h
 
#ifndef MYLIB_H
#define MYLIB_H
 
#ifdef MYLIB_EXPORTS
	#define DllExport __declspec(dllexport)
#else
	#define DllExport __declspec(dllimport)
#endif // MYLIB_EXPORTS
 
 
class MyLib
	{
	public:
		DllExport static MyLib* New();
		DllExport ~MyLib();
	private:
		DllExport MyLib();
	};
 
 
//Implementation of mylib.cpp//
DllExport MyLib* MyLib::New()
	{
	MyLib* mylib = new MyLib();
	return mylib;
	}
 
MyLib::MyLib()
	{}
 
MyLib::~MyLib()
	{}
 
// Executable implementation
#include "mylib.h"
 
int main()
{
MyLib* mylib = MyLib::New();
delete mylib; // this delete gives problem
}

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Question by:tusharganguli
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Accepted Solution

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evilrix earned 250 total points
ID: 21820235
You can only delete heap in the module it was allocated. This is because each module has its own heap. Uf you've allocated the heap in the DLL the DLL should also expose a function to allow pointer to the heap to be pass back in so it can be released.

http://blogs.msdn.com/oldnewthing/archive/2006/09/15/755966.aspx
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Author Closing Comment

by:tusharganguli
ID: 31468671
Thanks a lot for the explanation, and apologies for not aceepting this solution earlier, just have lost touch with EE for a long while now :-). Although I did understand the run time concept of memory allocation, but if you could still provide some links for understanding why is there such a discrepancy? what exactly do we mean by runtime being different? is this a phenomena only with windows dll or even linux libraries have these problems?
Would appreciate any further links or recommendation of books, I am eager to know what exactly is happening here.
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