Visual Studio 2015 strange failure in debug mode

Question

Hi,
I installed the latest vs 2015 on windows 7 (vmware) to test it compiling and running a set of applications (desktop) I have.
The compilation is ok but when I try to run one of those apps, I get this error (running the debug version):
Please note that if I run in release mode, there is no error at all!?
Following the call stack, it seems that it fails somewhere in the STL releasing a temporary string or something like that. Unfortunately, I cannot create just a small example showing the failure.
Any ideas of why will this failure be in debug mode only? Note that the call stack shows that this code:
    ~_String_alloc() _NOEXCEPT
        {    // destroy the object
        _Free_proxy();
is run from xstring and it fails calling "_Free_proxy();". Also note that this is called ONLY when _ITERATOR_DEBUG_LEVEL is defined. No such code is run in release mode.
Thanks,
G.

Answer 1

Hi,
I think I found the issue and here are some details, hopping that it will help others running in the same problem(s).
First, I did not have just the issue starting this thread, there was another issue related.
I have created a C++ DLL exporting common functions I used in various applications. Most of the time I used this DLL from console programs (servers). However I had two GUI programs where I also used this DLL, one based on MFC and the other on WTL.
These two programs have the issues as follows:
   When the MFC program is run in debug mode under the IDE, at exist the IDE will show a memory leak. This happened with both vs 2013 and vs 2015. This is a debug mode only issue.
   When the WTL program was run in debug mode under the IDE, it showed no problems at all when using vs 2013 but had the issue described at the starting of this thread under vs 2015. This is also a debug mode only issue.
It turned out that mfc issue was caused by a known bug in MFC where the termination code of the mfc app, is run BEFORE the termination of code of the DLL. This way the IDE give a false memory leak!! There were actually no memory leaks, just the false alarm!
I am not sure exactly what is going on in the WTL but the issue seems somehow similar in the sense that something not loaded in time from the DLL caused the problem.
The solution: For both projects in fact it was very easy to fix this issue by setting the option to delay load the DLL. That in turn will force the MFC to wait to first unload the DLL and then
there is no false leakage info! This also as I said fixed the WTL issue but I am not sure why? Anyway the WTL is no longer maintained (too bad!!) so who know?!
Bottom line: if you use DLLs from WTL or from MFC, delay load your DLLs! Otherwise you may get this nasty false flags in debug mode and the assert issue.
G.