stdvectorreserve
stdvectorreserve is a member function of the std::vector class in C++. It is used to request that the container capacity be at least enough to contain n elements. If n is greater than the current capacity, reserve causes the container's capacity to grow. If n is less than or equal to the current capacity, reserve does nothing. The capacity of a vector is the number of elements it can hold before needing to reallocate its internal storage.
Calling reserve() is a performance optimization. When a vector grows, it may need to reallocate memory and
If the new capacity is greater than the current capacity, all elements in the vector remain valid,