Visual Studio 22 - Diagnostic Tools - Memory Usage not showing memory leak

Question

I want to detect a simple memory leak using Visual Studio 22. I am using C++.

---

#include <iostream>

void leak(const unsigned numBytesToLeak)
{
    new char[numBytesToLeak];
}

int main()
{
    std::cout << "before" << std::endl; // breakpoint 1
    leak(646497);
    std::cout << "after" << std::endl; // breakpoint 2
}

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I am using the Debug build with optimizations set to /Od (off).

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I set two breakpoints around the line that causes the leak. I am running debugger and taking snapshots of my heap before and after the leak. What I think I should be seeing is an increase of the heap when I hit the second breakpoint. But I do not.

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Why is my memory leak not being detected?

Answer 1

Looking at the assembly when the program is compiled with /std:c++20 /W4 /O2 shows that the program indeed will leak, so the leak is not optimized away:

numBytesToLeak$ = 8
void leak(unsigned int) PROC                             ; leak, COMDAT
        mov     ecx, ecx
        jmp     void * operator new[](unsigned __int64)  ; operator new[]
void leak(unsigned int) ENDP                            ; leak

main    PROC                                            ; COMDAT
$LN6:
        sub     rsp, 40                                 ; 00000028H
        mov     ecx, 646497                             ; 0009dd61H
        call    void * operator new[](unsigned __int64) ; operator new[]
        xor     eax, eax
        add     rsp, 40                                 ; 00000028H
        ret     0
main    ENDP

However, VS2022 does not report this as a problem. Not even compiled with /fsanitize=address (which catches the leak in g++ and clang++ if compiled unoptimized) will it report the leak.

You'll most likely have to wait untill enough people have requested /fsanitize=leak to be added to Visual Studio too until such leaks will be caught.