CODEWITHSUNDEEP
c++memory-managementvoid-pointers
I am not smart
I am not smart

Reputation: 1441

How do I delete this Void Pointer?

#define ALIGNBUF(Length) Length % ALIGNSIZE ? \
              Length + ALIGNSIZE - (Length % ALIGNSIZE) : Length 

short NumCols;
long * ColLenArray, * OffsetArray;

ColLenArray = new long(NumCols * sizeof(long));
OffsetArray = new long(NumCols * sizeof(long));

// THIS CODE SHOULD NOT BE NEEDED TO UNDERSTAND THE PROBLEM
// BUT I HAVE INCLUDED IT JUST IN CASE
////////////////////////////////////////////////////////////
SQLColAttribute(hstmt, ((SQLUSMALLINT) i)+1, SQL_DESC_OCTET_LENGTH, NULL, 0, NULL, &ColLenArray[i]);
    ColLenArray[i] = ALIGNBUF(ColLenArray[i]);
    if (i)
        OffsetArray[i] = OffsetArray[i-1]+ColLenArray[i-1]+ALIGNBUF(sizeof(SQLINTEGER));
////////////////////////////////////////////////////////////

void **DataPtr = new void*[OffsetArray[NumCols - 1] + ColLenArray[NumCols - 1] + ALIGNBUF(sizeof(long))];

delete []DataPtr;

Don't think it can be done, have tried every way imaginable.

This code works, as in the program runs, I just can't deallocate the memory. Every time this code is called(not all code included as it isn't relevant) the memory gets bigger. I think that deletion is not happening properly and that the void * keeps growing.

I have also changed some of the code above based on recommendations here, but as this code is, the memory keeps growing.

Upvotes: 1

Views: 1887

Answers (3)

RobH
RobH

Reputation: 3338

You just want a block of memory that you can pass to some database library routines? Allocate thus:

char * buffer = new char[ len ];

len is the length of the buffer in bytes. To delete, simply do:

delete [] buffer;

You want a void* to pass to a function?

void * DataPtr = static_cast< void* >( buffer );

For extra merit points, use boost to manage deletion:

boost::scoped_array< char > buffer( new char[ len ] );

... then you don't have to worry about deletion. To get the buffer here, you need:

void * DataPtr = static_cast< void* >( buffer.get() );

Upvotes: 0

iammilind
iammilind

Reputation: 69988

You should try avoid mixing void* and new. In C++ actually, new is meant to automatically determine the type of the pointer; then why should not use it. At least you can use char*, if you are simply dealing with raw bytes.

Other point is new void*[SIZE] allocates void**. So you should change the declaration to void **DataPtr. Remove typecasting ahead of new. You can now delete[] DataPtr;.

Edit:

The code have some problems, the variables should be declared like below:

ColLenArray = new long[NumCols * sizeof(long)]; // declare as long[] (not long())
OffsetArray = new long[NumCols * sizeof(long)];

when you declare those variables as, new long(); it will simply initialize the value and assign a pointer to single long.

The memory corruption happens because, you are using ColLenArray[i], which is accessing wrong memory. Since you are going to use above variables as arrays, it should be new long[]. Then memory corruption will not happen. After usage, you should delete[] them.

Upvotes: 1

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272517

You can't invoke delete on a void *.

The solution is to not cast a pointer-to-void** (which is what new void*[...] will give you) to void*. I don't really know what your code is supposed to be doing, but have you tried changing the type of DataPtr to void **?

More generally, avoid void* as far as possible in C++. There are better solutions. If you edit your question to describe what you're trying to achieve, then we may be able to help suggest something.

Upvotes: 3

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