Thread: Memory deallocated.

You can use platform-specific functions like _msize() to get the size of an allocated block.

But instead of writing your own leak detector, you could just use a leak detector library. There are various.

Originally Posted by scarecrow

Well yes, that's a given. But how can I determine how much is in fact deallocated?

How do you mean?

In your (presumably common) actual memory allocation and deallocation routines, you store the size of the allocation. Whether it is plain new or new [], when you deallocation with delete or delete [], you should get the same pointer back to the corresponding delete function. You should allocate a bit extra memory [to make sure that you don't get alignment problems, make sure that this extra memory is a multiple of 16 bytes], and keep a linked list of all your allocations. If you want to check for "bad delete", run through the list and check that the original pointer is in there [and perhaps mark whether it is new or new[] that created the allocation, and that it matches with the delete call made].

--
Mats

Originally Posted by scarecrow

And suddenly I realise how simple and stupid my problem actually was. Thanks for some perspective.

So would I always allocate exactly 16 bytes? Or should I weight this to increase more (in multiples as you said) for larger allocations?

What I meant was that if you put a "block at the start of the allocation", it should be 16, 32, 48, 64, etc bytes. That way you will be guaranteed that you are not breaking any C library alignment rules.

And here's an example:

Code:

struct allocation
{
    int id;
    struct allocation *next;
    size_t size;
    int line;
    char *file;
    union {
       int fill[3];   // we have 5 integers above, so add another 3 to make 8 => 32 bytes. 
       double filld;   // This makes sure your allocation is in itself aligned to 8 bytes. 
    };
}

..
void *mymalloc(size_t size, char *file, int line)
{
    struct allocation *a;
    size_t fullsize = sizeof(*a) + size;
    a = malloc(fullsize);
    a->id = 12345678;
    a->size = size;
    a->file = file;
    a->line = line;
    ... insert a into linked list or some such. 
    return (void *)&a[1];
}

--
Mats

With malloc/free it's pretty easy:

Code:

#define malloc(size) mymalloc(size, _LINE__, __FILE__)
#define free(ptr) myfree(ptr, _LINE__, __FILE__)

Of course, make sure those macros are NOT in place when you define your mymalloc/myfree.

I think with new/delete, you have to be a bit more imaginative. I can't come up with a simple solution right now. I will have a think about it tho'.

--
Mats

Ah, paraphrazing Elysias suggestion:

Code:

struct FileLine
{
    char *file;
    int line;
    FileLine(int l, char *f) : line(l), file(f) {};
};

#define new new(FileLine(__FILE__, __LINE__))

Or something similar, at least.

--
Mats