Can I force std::vector to leave a memory leak?

Question

Can I force std::vector to not deallocate its memory after the vector goes out of scope?

For example, if I have

Answer 1

This is a bad idea, but possible by creating a custom allocator that does not deallocate as said in other answers.

For example : (boilerplate mostly from cppref)

#include 
#include 
#include 

template 
struct LeakingAllocator 
{
  using value_type = T;
  LeakingAllocator() = default;

  template  constexpr LeakingAllocator(const LeakingAllocator&) noexcept {}

  T* allocate(std::size_t n) 
  {
    if(n > std::size_t(-1) / sizeof(T)) throw std::bad_alloc(); // check for overflow

    if(auto p = static_cast(std::malloc(n*sizeof(T)))) return p; // return p if malloc returns a valid object
    throw std::bad_alloc(); // otherwise just throw.
  }

  void deallocate(T* p, std::size_t) noexcept { /*leak intentionally*/ }
};


template 
bool operator==(const LeakingAllocator&, const LeakingAllocator&) { return true; }
template 
bool operator!=(const LeakingAllocator&, const LeakingAllocator&) { return false; }

template 
using LeakingVector = std::vector>;

Then code like

int* ret()
{
    LeakingVector a;
    a.resize(10);
    return &a[0];
}

int main()
{
    auto ptr = ret();
    *ptr = 10;
    std::cout << *ptr;
}

becomes valid.