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            C++研究

            C++細節深度探索及軟件工程

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            By default, you should use a vector. It has the simplest internal data structure and
            provides random access. Thus, data access is convenient and flexible, and data
            processing is often fast enough.

            • If you insert and/or remove elements often at the beginning and the end of a sequence,
            you should use a deque. You should also use a deque if it is important that the amount of
            internal memory used by the container shrinks when elements are removed. Also,
            because a vector usually uses one block of memory for its elements, a deque might be
            able to contain more elements because it uses several blocks.

            • If you insert, remove, and move elements often in the middle of a container, consider
            using a list. Lists provide special member functions to move elements from one container
            to another in constant time. Note, however, that because a list provides no random access, you might suffer significant performance penalties on access to elements inside
            the list if you only have the beginning of the list.
            Like all node-based containers, a list doesn't invalidate iterators that refer to elements, as
            long as those elements are part of the container. Vectors invalidate all of their iterators,
            pointers, and references whenever they exceed their capacity, and part of their iterators,
            pointers, and references on insertions and deletions. Deques invalidate iterators,
            pointers, and references when they change their size, respectively.

            • If you need a container that handles exceptions in a way that each operation either
            succeeds or has no effect, you should use either a list (without calling assignment
            operations and sort() and, if comparing the elements may throw, without calling merge
            (), remove(), remove_if(), and unique(); see page 172) or an associative
            container (without calling the multiple-element insert operations and, if copying/assigning
            the comparison criterion may throw, without calling swap()). See Section 5.11.2, for a
            general discussion of exception handling in the STL and Section 6.10.10, for a table of
            all container operations with special guarantees in face of exceptions.

            • If you often need to search for elements according to a certain criterion, use a set or a
            multiset that sorts elements according to this sorting criterion. Keep in mind that the
            logarithmic complexity involved in sorting 1,000 elements is in principle ten times better
            than that with linear complexity. In this case, the typical advantages of binary trees apply.
            A hash table commonly provides five to ten times faster lookup than a binary tree. So if a
            hash container is available, you might consider using it even though hash tables are not
            standardized. However, hash containers have no ordering, so if you need to rely on
            element order they're no good. Because they are not part of the C++ standard library, you
            should have the source code to stay portable.

            Quoted from STL_tutorial_reference
            posted on 2007-04-21 14:39 常興龍 閱讀(287) 評論(0)  編輯 收藏 引用
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