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44-398: C++03 replaced the prior C++98 standard. C++03 was later replaced by C++11 . C++03 was primarily a bug fix release for the implementers to ensure greater consistency and portability. This revision addressed 92 core language defect reports, 125 library defect reports, and included only one new language feature: value initialization. Among the more noteworthy defect reports addressed by C++03

88-605: A container<T>::reference must be a true lvalue of type T . This is not the case with vector<bool>::reference , which is a proxy class convertible to bool . Similarly, the vector<bool>::iterator does not yield a bool& when dereferenced . There is a general consensus among the C++ Standard Committee and the Library Working Group that vector<bool> should be deprecated and subsequently removed from

132-476: A vector are stored contiguously. Like all dynamic array implementations, vectors have low memory usage and good locality of reference and data cache utilization. Unlike other STL containers, such as deques and lists , vectors allow the user to denote an initial capacity for the container. Vectors allow random access ; that is, an element of a vector may be referenced in the same manner as elements of arrays (by array indices). Linked-lists and sets , on

176-469: A dynamic array algorithm called tiered vectors that provides O ( n ) performance for insertions and deletions from anywhere in the array, and O ( k ) get and set, where k ≥ 2 is a constant parameter. Hashed array tree (HAT) is a dynamic array algorithm published by Sitarski in 1996. Hashed array tree wastes order n amount of storage space, where n is the number of elements in the array. The algorithm has O (1) amortized performance when appending

220-417: A fixed capacity that needs to be specified at allocation . A dynamic array is not the same thing as a dynamically allocated array or variable-length array , either of which is an array whose size is fixed when the array is allocated, although a dynamic array may use such a fixed-size array as a back end. A simple dynamic array can be constructed by allocating an array of fixed-size, typically larger than

264-541: A given container, all elements must belong to the same type. For instance, one cannot store data in the form of both char and int within the same container instance. Originally, only vector , list and deque were defined. Until the standardization of the C++ language in 1998, they were part of the Standard Template Library (STL), published by SGI . Alexander Stepanov , the primary designer of

308-508: A group of container class templates in the standard library of the C++ programming language that implement storage of data elements. Being templates , they can be used to store arbitrary elements, such as integers or custom classes. One common property of all sequential containers is that the elements can be accessed sequentially. Like all other standard library components, they reside in namespace std . The following containers are defined in

352-461: A large amount, such as doubling in size, and use the reserved space for future expansion. The operation of adding an element to the end might work as follows: As n elements are inserted, the capacities form a geometric progression . Expanding the array by any constant proportion a ensures that inserting n elements takes O ( n ) time overall, meaning that each insertion takes amortized constant time. Many dynamic arrays also deallocate some of

396-450: A list of four byte integers takes up approximately three times as much memory as a vector of integers. The forward_list data structure implements a singly linked list . deque is a container class template that implements a double-ended queue . It provides similar computational complexity to vector for most operations, with the notable exception that it provides amortized constant-time insertion and removal from both ends of

440-468: A much smaller constant. Naïve resizable arrays and linearly growing arrays may be useful when a space-constrained application needs lots of small resizable arrays; they are also commonly used as an educational example leading to exponentially growing dynamic arrays. C++ 's std::vector and Rust 's std::vec::Vec are implementations of dynamic arrays, as are the ArrayList classes supplied with

484-459: A node in a list is an ⁠ O ( n ) {\displaystyle O(n)} ⁠ operation that requires a list traversal to find the node that needs to be accessed. With small data types (such as ints) the memory overhead is much more significant than that of a vector. Each node takes up sizeof (type) + 2 * sizeof (type*) . Pointers are typically one word (usually four bytes under 32-bit operating systems), which means that

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528-471: A part of the list class and there are algorithms that are part of the C++ STL ( Algorithm (C++) ) that can be used with the list and forward_list class: The following example demonstrates various techniques involving a vector and C++ Standard Library algorithms, notably shuffling , sorting , finding the largest element, and erasing from a vector using the erase-remove idiom . The output will be

572-414: A series of objects to the end of a hashed array tree. In a 1999 paper, Brodnik et al. describe a tiered dynamic array data structure, which wastes only n space for n elements at any point in time, and they prove a lower bound showing that any dynamic array must waste this much space if the operations are to remain amortized constant time. Additionally, they present a variant where growing and shrinking

616-409: A significant amount of memory may still be available. There have been various discussions on ideal growth factor values, including proposals for the golden ratio as well as the value 1.5. Many textbooks, however, use a  = 2 for simplicity and analysis purposes. Below are growth factors used by several popular implementations: The dynamic array has performance similar to an array, with

660-415: Is available for allocation. The Standard Library defines a specialization of the vector template for bool . The description of this specialization indicates that the implementation should pack the elements so that every bool only uses one bit of memory. This is widely considered a mistake. vector<bool> does not meet the requirements for a C++ Standard Library container. For instance,

704-583: Is determined at compile-time by a template parameter. By design, the container does not support allocators because it's basically a C-style array wrapper. The containers are defined in headers named after the names of the containers, e.g. vector is defined in header <vector> . All containers satisfy the requirements of the Container concept , which means they have begin() , end() , size() , max_size() , empty() , and swap() methods. There are other operations that are available as

748-469: Is mitigated by the gap buffer and tiered vector variants discussed under Variants below. Also, in a highly fragmented memory region, it may be expensive or impossible to find contiguous space for a large dynamic array, whereas linked lists do not require the whole data structure to be stored contiguously. A balanced tree can store a list while providing all operations of both dynamic arrays and linked lists reasonably efficiently, but both insertion at

792-447: Is not currently using. Memory is freed when an element is removed from the list. Lists are efficient when inserting new elements in the list; this is an ⁠ O ( 1 ) {\displaystyle O(1)} ⁠ operation. No shifting is required like with vectors. Lists do not have random-access ability like vectors ( ⁠ O ( 1 ) {\displaystyle O(1)} ⁠ operation). Accessing

836-420: Is rare. Erasing elements from a vector or even clearing the vector entirely does not necessarily free any of the memory associated with that element. A typical vector implementation consists, internally, of a pointer to a dynamically allocated array, and possibly data members holding the capacity and size of the vector. The size of the vector refers to the actual number of elements, while the capacity refers to

880-418: Is to be added, then the underlying fixed-size array needs to be increased in size. Typically resizing is expensive because it involves allocating a new underlying array and copying each element from the original array. Elements can be removed from the end of a dynamic array in constant time, as no resizing is required. The number of elements used by the dynamic array contents is its logical size or size , while

924-555: The Java API and the .NET Framework . The generic List<> class supplied with version 2.0 of the .NET Framework is also implemented with dynamic arrays. Smalltalk 's OrderedCollection is a dynamic array with dynamic start and end-index, making the removal of the first element also O(1). Python 's list datatype implementation is a dynamic array the growth pattern of which is: 0, 4, 8, 16, 24, 32, 40, 52, 64, 76, ... Delphi and D implement dynamic arrays at

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968-473: The STL, bemoans the choice of the name vector , saying that it comes from the older programming languages Scheme and Lisp but is inconsistent with the mathematical meaning of the term. The array container at first appeared in several books under various names. Later it was incorporated into a Boost library, and was proposed for inclusion in the standard C++ library. The motivation for inclusion of array

1012-522: The addition of new operations to add and remove elements: Dynamic arrays benefit from many of the advantages of arrays, including good locality of reference and data cache utilization, compactness (low memory use), and random access . They usually have only a small fixed additional overhead for storing information about the size and capacity. This makes dynamic arrays an attractive tool for building cache -friendly data structures . However, in languages like Python or Java that enforce reference semantics,

1056-555: The affected elements are thus invalidated. In fact, any insertion can potentially invalidate all iterators. Also, if the allocated storage in the vector is too small to insert elements, a new array is allocated, all elements are copied or moved to the new array, and the old array is freed. deque , list and forward_list all support fast insertion or removal of elements anywhere in the container. list and forward_list preserves validity of iterators on such operation, whereas deque invalidates all of them. The elements of

1100-413: The array. Naïve resizable arrays are the simplest way of implementing a resizable array in C. They don't waste any memory, but appending to the end of the array always takes Θ( n ) time. Linearly growing arrays pre-allocate ("waste") Θ(1) space every time they re-size the array, making them many times faster than naïve resizable arrays -- appending to the end of the array still takes Θ( n ) time but with

1144-454: The buffer has not only amortized but worst-case constant time. Bagwell (2002) presented the VList algorithm, which can be adapted to implement a dynamic array. Naïve resizable arrays -- also called "the worst implementation" of resizable arrays -- keep the allocated size of the array exactly big enough for all the data it contains, perhaps by calling realloc for each and every item added to

1188-457: The current revision of the C++ standard: array , vector , list , forward_list , deque . Each of these containers implements different algorithms for data storage, which means that they have different speed guarantees for different operations: Since each of the containers needs to be able to copy its elements in order to function properly, the type of the elements must fulfill CopyConstructible and Assignable requirements. For

1232-451: The dynamic array depends on several factors including a space-time trade-off and algorithms used in the memory allocator itself. For growth factor a , the average time per insertion operation is about a /( a −1), while the number of wasted cells is bounded above by ( a −1) n . If memory allocator uses a first-fit allocation algorithm, then growth factor values such as a =2 can cause dynamic array expansion to run out of memory even though

1276-731: The dynamic array generally will not store the actual data, but rather it will store references to the data that resides in other areas of memory. In this case, accessing items in the array sequentially will actually involve accessing multiple non-contiguous areas of memory, so the many advantages of the cache-friendliness of this data structure are lost. Compared to linked lists , dynamic arrays have faster indexing (constant time versus linear time) and typically faster iteration due to improved locality of reference; however, dynamic arrays require linear time to insert or delete at an arbitrary location, since all following elements must be moved, while linked lists can do this in constant time. This disadvantage

1320-400: The element sequence. Unlike vector , deque uses discontiguous blocks of memory, and provides no means to control the capacity of the container and the moment of reallocation of memory. Like vector , deque offers support for random-access iterators , and insertion and removal of elements invalidates all iterators to the deque. array implements a non-resizable array . The size

1364-419: The elements. list supports bidirectional iteration, whereas forward_list supports only unidirectional iteration. array does not support element insertion or removal. vector supports fast element insertion or removal at the end. Any insertion or removal of an element not at the end of the vector needs elements between the insertion position and the end of the vector to be copied. The iterators to

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1408-479: The end and iteration over the list are slower than for a dynamic array, in theory and in practice, due to non-contiguous storage and tree traversal/manipulation overhead. Gap buffers are similar to dynamic arrays but allow efficient insertion and deletion operations clustered near the same arbitrary location. Some deque implementations use array deques , which allow amortized constant time insertion/removal at both ends, instead of just one end. Goodrich presented

1452-427: The following: Dynamic array In computer science , a dynamic array , growable array , resizable array , dynamic table , mutable array , or array list is a random access , variable-size list data structure that allows elements to be added or removed. It is supplied with standard libraries in many modern mainstream programming languages . Dynamic arrays overcome a limit of static arrays , which have

1496-407: The insertion point become invalidated. C++ vectors do not support in-place reallocation of memory, by design; i.e., upon reallocation of a vector, the memory it held will always be copied to a new block of memory using its elements' copy constructor, and then released. This is inefficient for cases where the vector holds plain old data and additional contiguous space beyond the held block of memory

1540-581: The language's core. Ada 's Ada.Containers.Vectors generic package provides dynamic array implementation for a given subtype. Many scripting languages such as Perl and Ruby offer dynamic arrays as a built-in primitive data type . Several cross-platform frameworks provide dynamic array implementations for C , including CFArray and CFMutableArray in Core Foundation , and GArray and GPtrArray in GLib . Common Lisp provides

1584-428: The number of elements immediately required. The elements of the dynamic array are stored contiguously at the start of the underlying array, and the remaining positions towards the end of the underlying array are reserved, or unused. Elements can be added at the end of a dynamic array in constant time by using the reserved space, until this space is completely consumed. When all space is consumed, and an additional element

1628-406: The other hand, do not support random access or pointer arithmetic. The vector data structure is able to quickly and easily allocate the necessary memory needed for specific data storage, and it is able to do so in amortized constant time. This is particularly useful for storing data in lists whose length may not be known prior to setting up the list but where removal (other than, perhaps, at the end)

1672-428: The size of the internal array. When new elements are inserted, if the new size of the vector becomes larger than its capacity, reallocation occurs. This typically causes the vector to allocate a new region of storage, move the previously held elements to the new region of storage, and free the old region. Because the addresses of the elements change during this process, any references or iterators to elements in

1716-441: The size of the underlying array is called the dynamic array's capacity or physical size , which is the maximum possible size without relocating data. A fixed-size array will suffice in applications where the maximum logical size is fixed (e.g. by specification), or can be calculated before the array is allocated. A dynamic array might be preferred if: To avoid incurring the cost of resizing many times, dynamic arrays resize by

1760-469: The standard library, while the functionality will be reintroduced under a different name. The list data structure implements a doubly linked list . Data is stored non-contiguously in memory which allows the list data structure to avoid the reallocation of memory that can be necessary with vectors when new elements are inserted into the list. The list data structure allocates and deallocates memory as needed; therefore, it does not allocate memory that it

1804-431: The underlying storage if its size drops below a certain threshold, such as 30% of the capacity. This threshold must be strictly smaller than 1/ a in order to provide hysteresis (provide a stable band to avoid repeatedly growing and shrinking) and support mixed sequences of insertions and removals with amortized constant cost. Dynamic arrays are a common example when teaching amortized analysis . The growth factor for

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1848-555: The vector become invalidated. Using an invalidated reference causes undefined behaviour . The reserve() operation may be used to prevent unnecessary reallocations. After a call to reserve(n), the vector's capacity is guaranteed to be at least n. The vector maintains a certain order of its elements, so that when a new element is inserted at the beginning or in the middle of the vector, subsequent elements are moved backwards in terms of their assignment operator or copy constructor . Consequently, references and iterators to elements after

1892-531: Was that it solves two problems of the C-style array: the lack of an STL-like interface, and an inability to be copied like any other object. It firstly appeared in C++ TR1 and later was incorporated into C++11 . The forward_list container was added to C++11 as a space-efficient alternative to list when reverse iteration is not needed. array , vector and deque all support fast random access to

1936-526: Was the library defect report 69, whose resolution added the requirement that elements in a vector are stored contiguously. This codifies the common expectation that a C++ std::vector object uses a memory layout similar to an array. While most implementations satisfied this expectation, it was not required by C++98. This programming-language -related article is a stub . You can help Misplaced Pages by expanding it . Sequence container (C%2B%2B)#Vector In computing, sequence containers refer to

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