Stack corruption

[miteshpandey]

I have a following member function prototype.

Dtk_Int32 ConvertToGeom(Geometric_set_select_entity **res = NULL) const;

If NULL is passed to the above function it returns the size of the output array;

I tried the following sets of code but I am getting stack corruption around the "entity" variable in each case when the function returns. If I remove the code altogether then there is no corruption and everything works fine.

Set 1:

Dtk_Int32 size = pLeaderPointer->ConvertToGeom(NULL);
Geometric_set_select_entity *entity = new Geometric_set_select_entity[size];
pLeaderPointer->ConvertToGeom(&entity);

Aussuming that I don't have to do the allocation and the function will:

Set 2:

Geometric_set_select_entity *entity = NULL;
Dtk_Int32 size = pLeaderPointer->ConvertToGeom(&entity);

The corruption again happens.

So I am in a doubt whether I am doing something wrong or the "ConvertToGeom" function is itself buggy.

Please help.

[Lindley]

What's the documentation on ConvertToGeom say it expects?

[miteshpandey]

The documentation is not upto the mark.

Here is what it says:

Dtk_Int32 Dtk_Leader::ConvertToGeom ( Geometric_set_select_entity ** res = NULL ) const

Converts the Dtk_Leader to geometrical elements.


Parameters:
outGeomsArray Geometrical elements array - or NULL -

Returns:
The number of geometrical elements.
Remarks:
If ConvertToGeom is used with NULL parameter, it only retrieves the number of geometrical elements.

And the most frustrating thing is that we don't have any of its usage example

Thanks,

[Lindley]

The suspicious thing is that the parameter is a **. That, to me, implies either that the function intends to reallocate its argument to size (as you deduced), or that it takes a 2D array. I don't know whether that would make any sense, however.

Do you happen to know if Geometric_set_select_entity is a POD class or not? If so, it's *possible* the function is expecting an array created with malloc, not new. I'd consider that unlikely, but you never know.

[Paul McKenzie]

I tried the following sets of code but I am getting stack corruption around the "entity" variable in each case when the function returns. If I remove the code altogether then there is no corruption and everything works fine.

Set 1:

Dtk_Int32 size = pLeaderPointer->ConvertToGeom(NULL);
Geometric_set_select_entity *entity = new Geometric_set_select_entity[size];
pLeaderPointer->ConvertToGeom(&entity);

The issue with your code above is that you've only allocated the "rows", and not the columns. It should look similar to the way you build a 2d array of ints or doubles. The problem is that the function doesn't return you the size of each row along with the number of rows.

However, I have never seen a function that takes a "T**", and have the user only allocate the rows alone. All the examples I know of requires the user to build the whole thing, rows and columns (starting with a T**).

You should contact whoever wrote the function to actually provide examples. Just having a "**" parameter doesn't convey any information by itself, as the author thought it intended.

Regards,

Paul McKenzie