C++ Memory Guidelines

1. Prefer stack allocation when possible

2. malloc() is usually fast, except when it isn’t

3. Prefer third party heap implementation on Windows

4. Reserve finaly container size when known rather than rely on geometric growth

5. Avoid using reserve() with constant delta in loops

6. Prefer output parameters to returns for containers

7. Reuse previous allocations when possible

8. Prefer memberwise .clear() over assignment to empty struct

9. Avoid using alloca() because it is likely to overflow the stack

10. Consider monotonic allocators when resources can be scoped and budgeted

11. Each feature on your allocator brings you closer to reimplementing malloc()

Conclusion

• Dynamic allocation comes at an unpredictable runtime cost
• Size-up allocations once and reuse containers as much as possible
• Consider monotonic allocators, but beware of going further

Reference

• Heaps Don’t Lie - Guidelines for Memory Allocation in C++ - Mathieu Ropert - ACCU 2025
• https://github.com/microsoft/mimalloc
• https://mropert.github.io/