C++ std::vector vs array in the real world

Question

I\'m new to C++. I\'m reading "Beginning C++ Through Game Programming" by Michael Dawson. However, I\'m not new to programming in general. I just finished a cha

Answer 1

I am going to pop my opinion in here for coding large sized array/vectors used in science and engineering.

The pointer based arrays in this case can be quite a bit faster especially for standard types. But the pointers add the danger of possible memory leaks. These memory leaks can lead to longer debug cycle. Additionally if you want to make the pointer based array dynamic you have to code this by hand.

On the other hand vectors are slower for standard types. They also are both dynamic and memory safe as long as you are not storing dynamically allocated pointers in the stl vector.

In science and engineering the choice depends on the project. how important is speed vs debug time? For example LAAMPS which is a simulation software uses raw pointers that are handled through their memory management class. Speed is priority for this software. A software I am building, i have to balance speed, with memory footprint and debug time. I really dont want to spend a lot of time debugging so i am using the STL vector.

I wanted to add some more information to this answer that I discovered from extensive testing of large scale arrays and lots of reading the web. So, another problem with stl vector and large sized arrays (one million +) occurs in how memory gets allocated for these arrays. Stl vector uses the std::allocator class for handling memory. This class is a pool based memory allocator. Under small scale loading the pool based allocation is extremely efficient in terms of speed and memory use. As the size of the vector gets into the millions, the pool based strategy becomes a memory hog. This happens because the pools tendency is to always hold more space than is being currently used by the stl vector.

For large scale vectors you are either better off writing your own vector class or using pointers (raw or some sort of memory management system from boost or the c++ library). There are advantages and disadvantages to both approaches. The choice really depends on the exact problem you are tackling (too many variables to add in here). If you do happen to write your own vector class make sure to allow the vector an easy way to clear its memory. Currently for the Stl vector you need to use swap operations to do something that really should have been built into the class in the first place.