Learning boost 2
Array
简介
boost::array是一个对c++数组的包装类。和stl::vector不同的是array和c++数组一样是一个静态大小的容器。请看下面的一个例子：
#include<boost/array.hpp>
#include<iostream>
using namespace std;
int main()
{
boost::array<int,5> a={1,2,3,4,5};
for (int i=0;i<5;++i)
cout<<a[i]<<endl;
return 0;
}
构造
array的原形是：
template<typename T, std::size_t N> class array;
T表示元素的类型，N表示容器的大小。在这里，容器的大小N是模板的一个参数，这意味着不同容器大小的array类型是不同的。
array并没有提供线式的构造函数，只提供了一个对等号运算符的重载。
template<typename U> array& operator=(const array<U, N>&);
构造函数，拷贝构造函数都是用默认的。可以使用如下方法来构造array
boost::array<int,5> a={1,2,3,4,5};
boost::array<int,5> b=a;//使用默认的拷贝构造函数
boost::array<int,5> c;//默认的构造函数，其中每个元素的值是未知的
boost::array<int,5> d={1,2,3};//最后两个元素的值未知
boost::array<int,5> e={1,2,3,4,5,6};//编译错误
boost::array<int,6> f=a;//编译错误，因为array<int,6>和array<int,5>类型不同
boost::array<double,5> g=a;//正确
访问
和vector一样,array既支持迭代器也支持operator[]和at();
operator[]不提供越界保护，而at成员对于越界访问会抛出一个异常。
array支持的迭代器有：
l iterator
l const_iterator
l reverse_iterator
l const_reverse_iterator
相关的成员函数：
l begin()
l end()
l rbegin()
l rend()
l front()
l back()
由于这些东西和stl中使用的方法一样，就不多说了。
另外array提供了data()和c_array()成员函数，data返回const T*，c_array返回T*，都返回c++形式的数组，但是注意data是const的成员函数，c_array不是。
由于array非常简单，下面附上array的源代码：
/* The following code declares class array,
* an STL container (as wrapper) for arrays of constant size.
*
* See
* http://www.josuttis.com/cppcode
* for details and the latest version.
* See
* http://www.boost.org/libs/array for Documentation.
* for documentation.
*
* (C) Copyright Nicolai M. Josuttis 2001.
* Distributed under the Boost Software License, Version 1.0. (See
* accompanying file LICENSE_1_0.txt or copy at
* http://www.boost.org/LICENSE_1_0.txt)
*
* 29 Jan 2004 - c_array() added, BOOST_NO_PRIVATE_IN_AGGREGATE removed (Nico Josuttis)
* 23 Aug 2002 - fix for Non-MSVC compilers combined with MSVC libraries.
* 05 Aug 2001 - minor update (Nico Josuttis)
* 20 Jan 2001 - STLport fix (Beman Dawes)
* 29 Sep 2000 - Initial Revision (Nico Josuttis)
*
* Jan 29, 2004
*/
#ifndef BOOST_ARRAY_HPP
#define BOOST_ARRAY_HPP
#include <cstddef>
#include <stdexcept>
#include <boost/assert.hpp>
// Handles broken standard libraries better than <iterator>
#include <boost/detail/iterator.hpp>
#include <algorithm>
// FIXES for broken compilers
#include <boost/config.hpp>
namespace boost {
template<class T, std::size_t N>
class array {
public:
T elems[N]; // fixed-size array of elements of type T
public:
// type definitions
typedef T value_type;
typedef T* iterator;
typedef const T* const_iterator;
typedef T& reference;
typedef const T& const_reference;
typedef std::size_t size_type;
typedef std::ptrdiff_t difference_type;
// iterator support
iterator begin() { return elems; }
const_iterator begin() const { return elems; }
iterator end() { return elems+N; }
const_iterator end() const { return elems+N; }
// reverse iterator support
#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) && !defined(BOOST_MSVC_STD_ITERATOR) && !defined(BOOST_NO_STD_ITERATOR_TRAITS)
typedef std::reverse_iterator<iterator> reverse_iterator;
typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
#elif defined(_MSC_VER) && (_MSC_VER == 1300) && defined(BOOST_DINKUMWARE_STDLIB) && (BOOST_DINKUMWARE_STDLIB == 310)
// workaround for broken reverse_iterator in VC7
typedef std::reverse_iterator<std::_Ptrit<value_type, difference_type, iterator,
reference, iterator, reference> > reverse_iterator;
typedef std::reverse_iterator<std::_Ptrit<value_type, difference_type, const_iterator,
const_reference, iterator, reference> > const_reverse_iterator;
#else
// workaround for broken reverse_iterator implementations
typedef std::reverse_iterator<iterator,T> reverse_iterator;
typedef std::reverse_iterator<const_iterator,T> const_reverse_iterator;
#endif
reverse_iterator rbegin() { return reverse_iterator(end()); }
const_reverse_iterator rbegin() const {
return const_reverse_iterator(end());
}
reverse_iterator rend() { return reverse_iterator(begin()); }
const_reverse_iterator rend() const {
return const_reverse_iterator(begin());
}
// operator[]
reference operator[](size_type i)
{
BOOST_ASSERT( i < N && "out of range" );
return elems[i];
}
const_reference operator[](size_type i) const
{
BOOST_ASSERT( i < N && "out of range" );
return elems[i];
}
// at() with range check
reference at(size_type i) { rangecheck(i); return elems[i]; }
const_reference at(size_type i) const { rangecheck(i); return elems[i]; }
// front() and back()
reference front()
{
return elems[0];
}
const_reference front() const
{
return elems[0];
}
reference back()
{
return elems[N-1];
}
const_reference back() const
{
return elems[N-1];
}
// size is constant
static size_type size() { return N; }
static bool empty() { return false; }
static size_type max_size() { return N; }
enum { static_size = N };
// swap (note: linear complexity)
void swap (array<T,N>& y) {
std::swap_ranges(begin(),end(),y.begin());
}
// direct access to data (read-only)
const T* data() const { return elems; }
// use array as C array (direct read/write access to data)
T* c_array() { return elems; }
// assignment with type conversion
template <typename T2>
array<T,N>& operator= (const array<T2,N>& rhs) {
std::copy(rhs.begin(),rhs.end(), begin());
return *this;
}
// assign one value to all elements
void assign (const T& value)
{
std::fill_n(begin(),size(),value);
}
// check range (may be private because it is static)
static void rangecheck (size_type i) {
if (i >= size()) {
throw std::range_error("array<>: index out of range");
}
}
};
// comparisons
template<class T, std::size_t N>
bool operator== (const array<T,N>& x, const array<T,N>& y) {
return std::equal(x.begin(), x.end(), y.begin());
}
template<class T, std::size_t N>
bool operator< (const array<T,N>& x, const array<T,N>& y) {
return std::lexicographical_compare(x.begin(),x.end(),y.begin(),y.end());
}
template<class T, std::size_t N>
bool operator!= (const array<T,N>& x, const array<T,N>& y) {
return !(x==y);
}
template<class T, std::size_t N>
bool operator> (const array<T,N>& x, const array<T,N>& y) {
return y<x;
}
template<class T, std::size_t N>
bool operator<= (const array<T,N>& x, const array<T,N>& y) {
return !(y<x);
}
template<class T, std::size_t N>
bool operator>= (const array<T,N>& x, const array<T,N>& y) {
return !(x<y);
}
// global swap()
template<class T, std::size_t N>
inline void swap (array<T,N>& x, array<T,N>& y) {
x.swap(y);
}
} /* namespace boost */
#endif /*BOOST_ARRAY_HPP*/
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