C++ std::array

std::array

template < class T, size_t N > class array;

Code Example

#include <iostream>
#include <array>
#include <cstring>

using namespace std;

int main(int argc, char **argv)
{
    array<int, 5> intArr = {1,2,3,4,5};
    for(auto it = intArr.begin(); it != intArr.end(); it++ )
    {
        cout << *it << "\t";
    }
    ///< output: 1  2   3   4   5

    cout << "\n";
    ///< r means reverse
    for(auto rit = intArr.rbegin(); rit < intArr.rend(); rit++)
    {
        cout << *rit << "\t";
    }
    ///< output: 5  4   3   2   1

    cout << "\n";
    ///< c means const
    for(auto cit = intArr.cbegin(); cit != intArr.cend(); cit++ )
    {
        cout << *cit << "\t";
    }
    ///< output:1   2   3   4   5

    cout << "\n";
    for(auto crit = intArr.crbegin(); crit < intArr.crend(); crit++)
    {
        cout << *crit << "\t";
    }
    ///< output:5   4   3   2   1

    cout << "\n";
    cout << "size of array:" << intArr.size() << "\n"; ///< output: 5
    cout << "sizeof array:" << sizeof intArr << "\n";  ///< output: 5

    cout << "\n";
    array<char, 10> arrCh = {'a','b','c','d','e'};
    cout << "size of array:" << arrCh.size() << "\n"; ///< output: 10
    cout << "max_size of array" << arrCh.max_size() << "\n"; ///< output: 10

    cout<< "\n";
    array<int, 0> first;
    array<int, 5> second;
    cout << "first array:" << first.empty() << "\n";
    ///< output: 1, means true
    cout << "second array:" << second.empty() << "\n";
    ///< output: 0, means false

    for(int i=0; i < second.size(); i++){
        second[i]=i;
    }

    for(auto it = second.begin(); it != second.end(); it++){
        cout << *it << "\t";
    }
    ///< output: 10 11  12  13  14

    for(int i=0; i < second.size(); i++){
        second.at(i) = i;
    }
    cout << "\n";
    for(int i=0; i< second.size(); i++){
        cout << second.at(i) << "\t";
    }
    ///< output:1   2   3   4   5

    array<int, 3> third = {1,2,3};
    for(int &x:third){
        cout << x << "\t";
    }
    ///< output:1   2   3

    cout << "\n";
    cout << "array::front():" << third.front() << "\n"; ///< output: 1
    cout << "array::back():" << third.back() << "\n";   ///< output: 3
    cout <<"modify front and back\n";
    third.front() == 11;
    third.back() = 22;
    cout << "array::front():" << third.front() << "\n"; ///< output: 11
    cout << "array::back():" << third.back() << "\n";   ///< output: 22

    const char * cstr = "Hello array";
    array<char, 20> arrChar;
    memcpy(arrChar.data(),cstr, strlen(cstr));
    cout << arrChar.data() << "\n";
    ///< output: Hello array

    array<int,10> fourth;
    fourth.fill(2);
    for(int &x:fourth){
        cout << x << "\t";
    }
    ///< output: 2  2   2   2   2   2   2   2   2   2

    array<int, 5> five = {1,2,3,4,5};
    array<int, 5> six = {6,7,8,9,0};
    five.swap(six);
    cout << "\n";
    for(int &x:five){
        cout << x << "\t";
    }
    ///< output: 6  7   8   9   0

    cout << "\n";
    for(int &x:six){
        cout << x << "\t";
    }
    ///< output:1   2   3   4   5

    array<int,5> a = {1,2,3,4,5};
    array<int,5> b = {1,2,3,4,5};
    array<int,5> c = {5,4,3,2,1};

    cout << "\n";
    /** They are both true */
    if( a == b ) cout << " a and b are equal!\n";
    if( b!=c ) cout << "b and c are not equal!\n";
    if( b < c ) cout << "b is less than c\n";
    if( c > b ) cout << "c is greater than b\n";
    if( a <= b ) cout << "a is less than or equal b\n";
    if( a >= b ) cout << "ais greater than or equal b\n";

    return 0;
}

Array class

Arrays are fixed-size sequence containers: they hold a specific number of elements ordered in a strict linear sequence.

Internally, an array does not keep any data other than the elements it contains (not even its size, which is a template parameter, fixed on compile time). It is as efficient in terms of storage size as an ordinary array declared with the language's bracket syntax ([]). This class merely adds a layer of member and global functions to it, so that arrays can be used as standard containers.

Unlike the other standard containers, arrays have a fixed size and do not manage the allocation of its elements through an allocator: they are an aggregate type encapsulating a fixed-size array of elements. Therefore,they cannot be expanded or contracted dynamically (see vector for a similar container that can be expanded).Zero-sized arrays are valid, but they should not be dereferenced (members front, back, and data).

Unlike with the other containers in the Standard Library, swapping two array containers is a linear operation that involves swapping all the elements in the ranges individually, which generally is a considerably less efficient

operation. On the other side, this allows the iterators to elements in both containers to keep their original container association.

Another unique feature of array containers is that they can be treated as tuple objects: The header overloads the get function to access the elements of the array as if it was a tuple, as well as specialized tuple_size

and tuple_element types.

Container properties

• Sequence:Elements in sequence containers are ordered in a strict linear sequence.Individual elements are accessed by their position in this sequence.
• Contiguous storage:The elements are stored in contiguous memory locations, allowing constant time random access to elements. Pointers to an element can be offset to access other elements.
• Fixed-size aggregate:The container uses implicit constructors and destructors to allocate the required space statically. Its size is compile-time constant. No memory or time overhead.

Template parameters

• T:Type of the elements contained. Aliased as member type array::value_type.
• N:Size of the array, in terms of number of elements.

In the reference for the array member functions, these same names are assumed for the template parameters.

Member types

The following aliases are member types of array. They are widely used as parameter and return types by member functions:

member	typedefinitio	notes
value_type	The first template parameter (T)
reference	value_type&
const_reference	const value_type&
pointer	value_type*
const_pointer	const value_type*
iterator	a random access iterator to value_type	convertible to const_iterator
const_iterator	a random access iterator to const value_type
reverse_iterator	reverse_iterator
const_reverse_iterator	reverse_iterator<const_iterator>
size_type	size_t	unsigned integral type
difference_type	ptrdiff_t

signed integral type

Member functions

Iterators

• begin: Return iterator to beginning (public member function )
• end: Return iterator to end (public member function )
• rbegin: Return reverse iterator to reverse beginning (public member function )
• rend: Return reverse iterator to reverse end (public member function )
• cbegin: Return const_iterator to beginning (public member function )
• cend: Return const_iterator to end (public member function )
• crbegin: Return const_reverse_iterator to reverse beginning (public member function )
• crend: Return const_reverse_iterator to reverse end (public member function )

Capacity

• size: Return size (public member function )
• max_size: Return maximum size (public member function )
• empty: Test whether array is empty (public member function )

Element access

• operator[]: Access element (public member function )
• at: Access element (public member function )
• front: Access first element (public member function )
• back: Access last element (public member function )
• data: Get pointer to data (public member function )

Modifiers

• fill: Fill array with value (public member function )
• swap: Swap content (public member function )

Non-member function overloads

• get (array): Get element (tuple interface) (function template )
• relational operators (array):Relational operators for array(function template )

Non-member class specializations

• tuple_element: Tuple element type for array (class template specialization )
• tuple_size: Tuple size traits for array (class template specialization )

参考文献

cplusplus

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