When to Choose Vector vs. List in the STL
According to Effective STL, the vector container should be the default choice for sequences. However, this recommendation requires further clarification.
Vector vs. List: Key Differences
To understand the distinction between vectors and lists, consider the following table:
Feature | Vector | List |
---|---|---|
Memory allocation | Contiguous | Non-contiguous |
Storage overhead | Pre-allocates space | Constant memory overhead |
Element space | No extra pointers | Extra space for node (pointers to next/previous) |
Memory reallocation | Can reallocate memory for entire vector | Never reallocates memory for entire list |
Insertion efficiency | O(1) at end, O(n) elsewhere | O(1) anywhere |
Erasure efficiency | O(1) at end, O(n) elsewhere | O(1) always |
Random access | Supported | Not supported |
Iterator validity | Invalidated after additions/removals | Remains valid after additions/removals |
Array access | Underlying array easily obtained | No underlying array available |
When List May Be Preferable
While vectors are generally more efficient, lists can be a better choice in specific scenarios:
- When constant insertions and deletions occur anywhere in the sequence. Lists allow for O(1) insertions and erasures regardless of their position.
- When iterators need to remain valid despite modifications to the sequence: Lists' iterators remain valid after additions and removals, making them suitable for situations where iterating through a changing sequence is required.
- When combining lists is desired: Lists provide a convenient way to combine and splice multiple lists efficiently.
- When memory overhead is a concern: Lists have lower memory overhead than vectors, making them a good choice for scenarios where memory is constrained.
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