Memory leak implementing custom allocator in C++17 using std::vector
I'm stuck trying to I'm getting frustrated with I've looked through the documentation and I'm still confused about I'm stuck on something that should probably be simple... I'm working on a performance-sensitive application that utilizes C++17, and I implemented a custom allocator for `std::vector` to manage memory allocation more efficiently. However, I'm working with unexpected memory leak issues when I resize the vector, which I need to seem to debug. The custom allocator is derived from `std::allocator` and overrides the necessary methods. Here's a simplified version of my allocator: ```cpp #include <memory> #include <iostream> #include <vector> template <typename T> class CustomAllocator : public std::allocator<T> { public: using value_type = T; CustomAllocator() = default; template <typename U> CustomAllocator(const CustomAllocator<U>&) {} T* allocate(std::size_t n) { std::cout << "Allocating " << n << " elements" << std::endl; return static_cast<T*>(::operator new(n * sizeof(T))); } void deallocate(T* p, std::size_t n) { std::cout << "Deallocating " << n << " elements" << std::endl; ::operator delete(p); } }; int main() { std::vector<int, CustomAllocator<int>> myVec; myVec.push_back(1); myVec.push_back(2); myVec.resize(5); return 0; } ``` Despite implementing the `allocate` and `deallocate` functions, I noticed that after multiple resizes, the program reports a memory leak when profiling. The specific behavior I receive from Valgrind is: ``` ==12345== 32 bytes in 1 blocks are definitely lost in loss record 1 of 1 ``` I suspect the question is related to how I'm handling the memory in the `resize` method of `std::vector`. I remembered that `std::vector` first allocates a new memory block when increasing its size, then moves the elements and finally calls the `deallocate` method on the old memory block. However, I'm not sure if my allocator's `deallocate` method is being called properly during this process. I've tried adding additional logging in my `deallocate` method to confirm if it's being invoked, but I sometimes see mismatched allocation and deallocation counts. Could anyone shed some light on what might be going wrong with my custom allocator and how I can resolve these memory leaks? What am I doing wrong? My development environment is Linux. I'd really appreciate any guidance on this. I'm open to any suggestions. Any feedback is welcome! What are your experiences with this?