a problem of access violation

[jayjay60]

Hello everybody,

In a new application, which a dialog box application i have a message error which appears and which tell me:

" Unhandld exception in Fractal_v1_0.exe(MSVCRTD.DLL):0xC0000005:Access Violation"

(Fractal_v1_0 is the name of my project!)

So, i meet often the problem "Access Violation" caused by mistake in memory allocation for different pointers, but here i don't understand!

so if someone could help me!

thanks in advance for your answers

jayjay60

 

[MKuiper]

Do you mean you don't understand the error occurs in MSVCRTD.dll and not in your program? Well, for example try this: strcat ( NULL, NULL ); Access violation guaranteed, and it will occur in one of the C runtime libraries, because it is detected there. The real error however, is in your program. If you want help with this you must give us some code.

Marcel

 

[EORCandy]

Without seeing some code, the only thing I can think of is the following scenario:

I'll use a hypothetical function called theFunc that takes a CComboBox* as a parameter.

Assume you encounter documentation that says "pass a pointer to a CComboBox in the call to theFunc(CComboBox* pCB)"

Do NOT do the following, this more than likely will give you the cheery "Access Violation" message (This fails because the pointer is not pointing to a valid CComboBox):

CComboBox* pCB // Invalid CComboBox pointer;

theFunc(pCB); // Oops! pCB is pointing to garbage!


This is what you should do (This works because oCB will be passed in a pointer to a valid ComboBox via the address of (&) operator):

CComboBox oCB;

theFunc(&oCB);


The following will work as well. (Note the difference between this and the first example (and remember to call "delete pCB;" BEFORE pCB goes out of scope otherwise you will have a memory leak!));

CComboBox* pCB; // Invalid CComboBox pointer

pCB = new CComboBox(); // Storage is allocated here. pCB is
// now pointing to a valid CComboBox.
theFunc(pCB);



If the function truly does take a pointer and not a pointer to storage, the function should be documented as (again note the pointer to pointer declaration):

theFunc(CComboBox** pCB);



Be very careful of this type of error. It is really easy to make this mistake (and I speak from first-hand experience with this!)

Happy coding! Hope this helps.

*~-> EOR Candy <-~*