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new operator .

Posted on 2000-04-28
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Last Modified: 2010-04-02
I use VC++ 5.0
I define a class like that
class FACT
{ char * content}
after that I init an array
 arr=new FACT[3];
but it allocate 4 elements each 32 bits.
the first elements contain number of elements in the array(3),and then "Debug assertion failed" because of arr point to the second elements so it can't free the mem .
How can I allocate only 3 elements by new operator.
Thanks.
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Question by:tungsim
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nietod earned 50 total points
ID: 2760554
>> but it allocate 4 elements each 32 bits.
In VC (and most C++ implimentations as well) when you allocate an array with new [] operator it alocates a little extra space for recording the number of items in the array.  this extra space if for the "private" use of the  c++ implimentation.  In particular, it is is for the use of the delete [] operator.  You should not be concerd about this extra memory.  it is necessary, not a problem, and not something for you to fool with.  Note that the memory is an extra integer (or some size integral) amount. it is not an entire extra element in the array beign allocated.  Like if you allocate an array of 10 big objects, it won't allocate space for 11 objects, just space for 10 plus a little extra  (4 bytes in VC).

continues
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LVL 22

Expert Comment

by:nietod
ID: 2760567
>> "Debug assertion failed"
Now where do you get this error?  is it when you delete?   do you delete using "delete" or using delete []"?  If you allocate with new []" you must delete with "delete []"  Like

arr=new FACT[3];
delete [] arr;

not

delete arr; // this is an error.

Let me know if you have any questions.
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Author Comment

by:tungsim
ID: 2761469
Thanks nietod .
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