Dynamically sized array at end of struct, C++ (vc++)

Dynamically sized array at end of struct

//Microsoft (R) C/C++ Optimizing Compiler Version 19.00.23506 for x64

#include <iostream>
#include <Windows.h>

struct MyStructPtr
{
    UINT  src;
    UINT  dst;
    UINT* pRects;
};

struct MyStructArr
{
    UINT  src;
    UINT  dst;
    UINT  pRects[1];
};

int main()
{
    MyStructPtr ptr = { };
    MyStructArr arr = { };
    
    // This causes the app to crash
    // ptr.pRects[0] = 1;
    
    arr.pRects[0] = 1;
    
    // This causes the app to crash
    // std::cout << ptr.pRects[0] << std::endl;
    
    std::cout << arr.pRects[0] << std::endl;
    
    const UINT sizePlusThreeSlots = sizeof(MyStructArr) + sizeof(UINT) * 3;
    MyStructArr* pArr = reinterpret_cast<MyStructArr*>(malloc(sizePlusThreeSlots));
    if (pArr != nullptr)
    {
        pArr->pRects[0] = 1;
        pArr->pRects[1] = 2;
        pArr->pRects[2] = 3;
        pArr->pRects[3] = 4;
        
        std::cout << pArr->pRects[0] << std::endl;
        std::cout << pArr->pRects[1] << std::endl;
        std::cout << pArr->pRects[2] << std::endl;
        std::cout << pArr->pRects[3] << std::endl;
        
        free(pArr);
    }
}


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