Nicolai Josuttis 2001 2002 2003 2004 Nicolai M. Josuttis Permission to copy, use, modify, sell and distribute this software is granted provided this copyright notice appears in all copies. This software is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose. STL compliant container wrapper for arrays of constant size

The C++ Standard Template Library STL as part of the C++ Standard Library provides a framework for processing algorithms on different kind of containers. However, ordinary arrays don't provide the interface of STL containers (although, they provide the iterator interface of STL containers). As replacement for ordinary arrays, the STL provides class std::vector. However, std::vector<> provides the semantics of dynamic arrays. Thus, it manages data to be able to change the number of elements. This results in some overhead in case only arrays with static size are needed. In his book, Generic Programming and the STL, Matthew H. Austern introduces a useful wrapper class for ordinary arrays with static size, called block. It is safer and has no worse performance than ordinary arrays. In The C++ Programming Language, 3rd edition, Bjarne Stroustrup introduces a similar class, called c_array, which I (Nicolai Josuttis) present slightly modified in my book The C++ Standard Library - A Tutorial and Reference, called carray. This is the essence of these approaches spiced with many feedback from boost. After considering different names, we decided to name this class simply array. Class array fulfills most but not all of the requirements of "reversible containers" (see Section 23.1, [lib.container.requirements] of the C++ Standard). The reasons array is not an reversible STL container is because: No constructors are provided. Elements may have an undetermined initial value (see ). swap() has no constant complexity. size() is always constant, based on the second template argument of the type. The container provides no allocator support. It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that: front() and back() are provided. operator[] and at() are provided.

STL compliant container wrapper for arrays of constant size T T* const T* std::reverse_iterator<iterator> std::reverse_iterator<const_iterator> T& const T& std::size_t std::ptrdiff_t size_type N const array<U, N>& std::copy(rhs.begin(),rhs.end(), begin()) iterator const_iterator iterator for the first element will not throw iterator const_iterator iterator for position after the last element will not throw reverse_iterator const_reverse_iterator reverse iterator for the first element of reverse iteration reverse_iterator const_reverse_iterator reverse iterator for position after the last element in reverse iteration size_type N bool N==0 will not throw size_type N will not throw reference size_type const_reference size_type i < N element with index i will not throw. reference size_type const_reference size_type element with index i std::range_error if i >= N reference const_reference N > 0 the first element will not throw reference const_reference N > 0 the last element will not throw const T* elems will not throw T* elems will not throw void array<T, N>& std::swap_ranges(begin(), end(), other.begin()) linear in N void const T& std::fill_n(begin(), N, value) T void array<T, N>& array<T, N>& x.swap(y) will not throw. bool const array<T, N>& const array<T, N>& std::equal(x.begin(), x.end(), y.begin()) bool const array<T, N>& const array<T, N>& !(x == y) bool const array<T, N>& const array<T, N>& std::lexicographical_compare(x.begin(), x.end(), y.begin(), y.end()) bool const array<T, N>& const array<T, N>& y < x bool const array<T, N>& const array<T, N>& !(y < x) bool const array<T, N>& const array<T, N>& !(x < y)

There was an important design tradeoff regarding the constructors: We could implement array as an "aggregate" (see Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would mean: An array can be initialized with a brace-enclosing, comma-separated list of initializers for the elements of the container, written in increasing subscript order: boost::array<int,4> a = { { 1, 2, 3 } }; Note that if there are fewer elements in the initializer list, then each remaining element gets default-initialized (thus, it has a defined value). However, passing no initializer list means that the elements have an indetermined initial value. It has no user-declared constructors. It has no private or protected non-static data members. It has no base classes. It has no virtual functions. The current implementation uses this approach. However, being able to have indeterminate initial values is a big drawback. So, please give me some feedback, how useful you consider this feature to be.

Do we want initializer list support or would the following be OK?: int data[] = { 1, 2, 3, 4 } boost::array<int,5> x(data); // or boost::array<int,data> x; Could "{ ... }" be used portably instead of "{ { ... } }" to initialize values? 8.5.1 (11) of the Standard seems to allow it; however, gcc 2.95.2 prints a warning message. Any way to have determinate initial values and initializer list support? Static_casts for reverse iterator stuff? I'd appreciate any constructive feedback. Please note: I don't have time to read all boost mails. Thus, to make sure that feedback arrives me, please send me a copy of each mail regarding this class.

To find more details about using ordinary arrays in C++ and the framework of the STL, see e.g. The C++ Standard Library - A Tutorial and Reference by Nicolai M. Josuttis Addison Wesley Longman, 1999 ISBN 0-201-37926-0 Home Page of Nicolai Josuttis

Doug Gregor ported the documentation to the BoostBook format.