Why stl:vector put in CArray causes error

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Hi,
Recently i've found strange error;

class ca
{
public:
int m_a;
};

class cb
{
public:
vector<ca> m_v;
};

CArray<cb, cb&> my_arr;
ca ca_elem;
cb cb_elem;
my_arr.Add(cb_elem);
my_arr.Add(cb_elem);
my_arr[0].m_v.push_back(ca_elem);  //this line causes crash,

i can't catch here any kind of exception and i don't know why error occurs.
I suppose that this is related with vector's memory allocation but i don't understand why.

Error occurs only on release.
There is CArray because it is old project, now i try to use stl containers

Can anyone explain why this error occurs?

Regards

Posted 12-Jan-16 1:39am

J. Andrzej

Updated 12-Jan-16 20:07pm

v3

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Comments

CPallini 12-Jan-16 8:48am

As it stands, it cannot crash, in my opinion. What about posting the actual code?

Albert Holguin 12-Jan-16 15:03pm

Yep, I'll have to second CPallini... don't think that would crash as written in the post.

Sergey Alexandrovich Kryukov 12-Jan-16 10:45am

As to the exception, how did you try to catch it?
—SA

Aescleal 12-Jan-16 17:26pm

Does the code you've presented work when it's the only code in the program? i.e. wrap it in int main() with the relevant includes and see what happens.

What compiler are you using?

Are there any weird and wonderful macros kicking about that might confuse things (e.g. MS are very fond of redefining new in MFC in debug versions)?

Does adding an explicit copy constructor and assignment operator in the contained classes do anything?

Have you read the source code for CArray to see if you can get a handle on what's happening? (It's ghastly BTW)

Albert Holguin 12-Jan-16 23:23pm

...although the purpose of redefining new in debug mode is to prevent this type of crashing for debugging (detect overflows/ invalid memory access)... so I doubt that's the cause of a crash.

J. Andrzej 13-Jan-16 2:28am

I corrected source code in question. If i add cb_elem two times to CArray error occurs when i try to push_back ca_elem to vector.

I couldnt catch any kind of exception: std::exception& e, CException *, even (...) (program compiled with SEH Exceptions)

I've found something on msdn

Most methods that resize a CArray object or add elements to it use memcpy_s to move elements.This is a problem because memcpy_s is not compatible with any objects that require the constructor to be called.If the items in the CArray are not compatible with memcpy_s, you must create a new CArray of the appropriate size.You must then use CArray::Copy and CArray::SetAt to populate the new array because those methods use an assignment operator instead of memcpy_s.

Does it mean that copy constructor is ommited and in CArray we shouldn't use objects that needs copy constructor

Aescleal 13-Jan-16 6:10am

The rule is don't change the size of a CArray after an initial SetSize (implied or otherwise) with objects that have a non-trivial copy constructor. Have a look at the source code and you'll see the problem.

Actually the rule should be don't use collection classes written by a bunch of C programmers that prefer bit fiddling to making their code robust...

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