Why You shouldn't mix microsoft dynamic runtimes in your applications

This sample illustrates the flaw you expose your native application
when linking against multiple Microsoft dynamic runtimes

The sample is composed of two dynamic libraries : malloc-vs8_debug.dll and malloc-vs9_debug.dll
and an executable.
malloc-vs8_debug.dll is linked against msvcr80d.dll and malloc-vs9_debug.dll is linked against msvcr90d.dll
the test_crt executable can be linked either against Microsft Debug 8.0 CRTs (msvcr80d) or Microsft Debug 9.0 CRTs (msvcr90d) dlls :

This sample is using Microsoft compilers and linker tools, meanwhile do not focus on this:
the __declspec is a compiler specific langage extension , dont focus on this neither:

malloc-vs9_debug.dll source :

#include <stdlib.h>

__declspec(dllexport) void *malloc_vs9(size_t sz)
{
	return malloc(sz);
}

__declspec(dllexport) void free_vs9(void *mem)
{
	free(mem);
}


and malloc-vs8_debug.dll source is:

#include <stdlib.h>

__declspec(dllexport) void *malloc_vs8(size_t sz)
{
	return malloc(sz);
}

__declspec(dllexport) void free_vs8(void *mem)
{
	free(mem);
}

while test_crt.exe is :


#pragma comment(lib,"malloc-vs9_debug.lib")
 
#pragma comment(lib,"malloc-vs8_debug.lib")
 

__declspec(dllimport) void *malloc_vs8(size_t sz);
__declspec(dllimport) void free_vs8(void *mem);
__declspec(dllimport) void *malloc_vs9(size_t sz);
__declspec(dllimport) void free_vs9(void *mem);

int main()
{
	void *mem = malloc_vs8(1);
	free_vs9(mem);
 //res = _CrtCheckMemory ();
	return 0; // if getting there return 0 we passed: check your compiler settings
}

test_crt will assert as follows:

HEAP[test_crt.exe]: Invalid Address specified to RtlValidateHeap( ..., ...)
This may be due to a corruption of the heap, and indicates a bug in test_crt.exe or any of the DLLs it has loaded. 

when calling free from free_vs9




A correct version might be:

__declspec(dllimport) void *malloc_vs8(size_t sz);
__declspec(dllimport) void free_vs8(void *mem);


int main()
{
	
	void *mem_vs8 = malloc_vs8(1);
	free_vs8(mem_vs8);
 //res = _CrtCheckMemory ();
	return 0;
}

Note that : 

__declspec(dllimport) void *malloc_vs8(size_t sz);
__declspec(dllimport) void free_vs8(void *mem);
__declspec(dllimport) void *malloc_vs9(size_t sz);
__declspec(dllimport) void free_vs9(void *mem);

int main()
{
	
 void *mem_vs9;
	void *mem_vs8 = malloc_vs8(1);
	free_vs8(mem_vs8);
	
	mem_vs9 = malloc_vs9(1);
	free_vs9(mem_vs9); //res = _CrtCheckMemory ();
	return 0;
}

is correct.




Meanwhile, don't be disappointed if you are not familiar with the above :
Compare it with the following situation :
You get credit from one bank ,
and pay back the loan to another one :
The second banker should (you must read must) advise you 
about your mistake and abort the transaction.  
In the above , the software will stop functionning,
meanwhile there are several ways to handle such failures.
Best practices should avoid such situations.

 
You have been warned you can go to either: GIMPVS Home Page

or: GTK+ SDK Quick Start Guide

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