CODEWITHSUNDEEP
c++memory-leaks
Matthew Hoggan
Matthew Hoggan

Reputation: 7594

MSVC _Crt* Macros Are not Safe to use in RAII Code

The code below produces a memory leak when there is none. Is it safe to say that Microsoft missed the mark on this one?

#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>

template <typename T>
class class_leak
{
private:
    T *p_;

public:
    class_leak(T *p) :
        p_(p)
    {}

    ~class_leak()
    {
        delete p_;
    }
};

int main(int /*argc*/, char * /*argv*/[]) {
    int *x = new int(10);
    class_leak<int> cl(x);
    _CrtDumpMemoryLeaks();
}

Prodcues:

Detected memory leaks!
Dumping objects ->
{56} normal block at 0x000D1540, 4 bytes long.
 Data: <    > 0A 00 00 00 
Object dump complete.
The program '[4584] unique_ptr.exe: Native' has exited with code 0 (0x0).

Upvotes: 0

Views: 69

Answers (1)

MSalters
MSalters

Reputation: 179930

The leak detection is indeed a bit simplistic. It checks just the current balance of allocations, not what memory can still be freed. Doesn't need RAII or even C++ to demonstrate that:

int *p = malloc(10);
_CrtDumpMemoryLeaks();
free(p);

Upvotes: 2

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