c++ array模板類使用
目錄
本章是對c++ array模板類的知識歸納,講述了c++中array模板類的使用,不涉及原理方面的內容。
c++中的陣列型別是繼承了c語言的特性,在使用陣列的時候要注意陣列越界操作問題。為了更安全的對陣列進行操作,c++提出了陣列模板類array。
1、array模板類的定義
(1)array模板類的宣告
template <class T,size_t N> class array;
陣列類是固定大小的序列容器,它們包含以嚴格線性序列排序的特定數量的元素。陣列類具有固定大小,並且不通過分配器管理其元素的分配,它們是封裝固定大小元素陣列的聚合型別。
(2)容器屬性
- 序列容器中的元素按嚴格的線性順序排序。各個元素按其順序訪問它們的位置。
- 元素儲存在連續的儲存器位置,允許對元素進行恆定時間隨機訪問。可以偏移元素的指標以訪問其他元素。
- 容器使用隱式建構函式和解構函式靜態分配所需的空間。它的大小是編譯時常量。沒有記憶體或時間開銷。
(3)array模板類的說明
array模板類中T為包含元素的型別(std::array::value_type),N為元素個數。
(4)array模板類標頭檔案
使用array模板類之前需要包含#include <array>標頭檔案!
2、array模板類的使用
(1)Iterators
Iterators迭代器的作用是遍歷array陣列類中的元素。可以通過begin/end()、rbegin/rend()、cbegin/cend()、crbegin/crend()等函式進行訪問。
begin | Return iterator to beginning |
end | Return iterator to end |
rbegin | Return reverse iterator to reverse beginning |
rend | Return reverse iterator to reverse end |
cbegin | Return const_iterator to beginning |
cend | Return const_iterator to end |
crbegin | Return const_reverse_iterator to reverse beginning |
crend | Return const_reverse_iterator to reverse end |
參考程式碼如下所示:
/*****************************************************
Copyright (C) 2018. All rights reserved.
File name : array.cpp
Version : v1.0
Author : zhengqijun
Date : 2018-08-10
Function List :
Description : array container.
******************************************************/
#include <iostream>
#include <array>
int main(void) {
std::array<int, 5> arr = {1, 2, 3, 4, 5};
std::cout << "array values: ";
for (auto it = arr.begin(); it != arr.end(); ++it) {
std::cout << *it << " ";
}
std::cout << std::endl;
return 0;
}
執行結果如下所示:
array values: 1 2 3 4 5
(2)Capacity
array陣列容器的大小是固定的。可以通過sizeof()、size()、max_size()、empty()等函式進行檢測。
size | Return size |
max_size | Return maximum size |
empty | Test whether list is empty |
測試array陣列容器大小的參考程式碼如下所示:
/*****************************************************
Copyright (C) 2018. All rights reserved.
File name : array.cpp
Version : v1.0
Author : zhengqijun
Date : 2018-08-10
Function List :
Description : array container.
******************************************************/
#include <iostream>
#include <array>
int main(void) {
std::array<int, 5> arr = {1, 2, 3, 4, 5};
std::cout << "sizeof(array) = " << sizeof(arr) << std::endl;
std::cout << "size of array = " << arr.size() << std::endl;
std::cout << "max_size of array = " << arr.max_size() << std::endl;
if (arr.empty()) {
std::cout << "array is empty!" << std::endl;
} else {
std::cout << "array is not empty!" << std::endl;
}
return 0;
}
執行結果如下所示:
sizeof(array) = 20
size of array = 5
max_size of array = 5
array is not empty!
(3)Element access
可以通過下標[ ]、at()、front()、back()、data()等函式訪問array容器內的元素。
operator[ ] | Access element |
at | Access element |
front | Access first element |
back | Access last element |
data | Get pointer to first data |
參考程式碼如下:
/*****************************************************
Copyright (C) 2018. All rights reserved.
File name : array.cpp
Version : v1.0
Author : zhengqijun
Date : 2018-08-10
Function List :
Description : array container.
******************************************************/
#include <iostream>
#include <array>
int main(void) {
std::array<int, 5> arr = {1, 2, 3, 4, 5};
std::cout << "array[0] = " << arr[0] << std::endl;
std::cout << "array.at(4) = " << arr.at(4) << std::endl;
std::cout << "array.front() = " << arr.front() << std::endl;
std::cout << "array.back() = " << arr.back() << std::endl;
std::cout << "&array: " << arr.data() << " = " << &arr << std::endl;
return 0;
}
執行結果如下所示:
array[0] = 1
array.at(4) = 5
array.front() = 1
array.back() = 5
&array: 0x7ffd22df6e50 = 0x7ffd22df6e50
(4)Modifiers
可以使用fill()、swap()等函式對array容器整體進行操作。
fill | Fill array with value |
swap | Swap content |
參考程式碼如下所示:
/*****************************************************
Copyright (C) 2018. All rights reserved.
File name : array.cpp
Version : v1.0
Author : zhengqijun
Date : 2018-08-10
Function List :
Description : array container.
******************************************************/
#include <iostream>
#include <array>
int main(void) {
std::array<int, 5> arr;
arr.fill(5); // fill
std::cout << "array values: ";
for (auto i : arr) {
std::cout << i << " ";
}
std::cout << std::endl;
std::array<int, 3> first = {1, 2, 3};
std::array<int, 3> second = {6, 5, 4};
std::cout << "first array values: ";
for (auto it = first.begin(); it != first.end(); ++it) {
std::cout << *it << " ";
}
std::cout << std::endl;
std::cout << "second array values: ";
for (auto it = second.begin(); it != second.end(); ++it) {
std::cout << *it << " ";
}
std::cout << std::endl;
first.swap(second); // swap
std::cout << "swap array success!" << std::endl;
std::cout << "first array values: ";
for (auto it = first.begin(); it != first.end(); ++it) {
std::cout << *it << " ";
}
std::cout << std::endl;
std::cout << "second array values: ";
for (auto it = second.begin(); it != second.end(); ++it) {
std::cout << *it << " ";
}
std::cout << std::endl;
return 0;
}
執行結果如下所示:
array values: 5 5 5 5 5
first array values: 1 2 3
second array values: 6 5 4
swap array success!
first array values: 6 5 4
second array values: 1 2 3
(5)Compare
還可以使用> < ==等符號對兩個array陣列容器進行比較。
/*****************************************************
Copyright (C) 2018. All rights reserved.
File name : array.cpp
Version : v1.0
Author : zhengqijun
Date : 2018-08-10
Function List :
Description : array container.
******************************************************/
#include <iostream>
#include <array>
int main(void) {
std::array<int,5> a = {10, 20, 30, 40, 50};
std::array<int,5> b = {10, 20, 30, 40, 50};
std::array<int,5> c = {50, 40, 30, 20, 10};
if (a == b) {
std::cout << "a == b" << std::endl;
} else {
std::cout << "a != b" << std::endl;
}
if (a == c) {
std::cout << "a == c" << std::endl;
} else {
std::cout << "a != c" << std::endl;
}
if (a < c) {
std::cout << "a < c" << std::endl;
} else {
std::cout << "a >= c" << std::endl;
}
return 0;
}
執行結果如下所示:
a == b
a != c
a < c
(6)Other
c++過載了get()函式來訪問陣列容器中的元素,為了和元組相似,還過載了tuple_size和tuple_element型別。
get( array) | Get element (tuple interface) |
tuple_element<array> | Tuple element type for array |
tuple_size<array> | Tuple size traits for array |
參考程式碼如下所示:
/*****************************************************
Copyright (C) 2018. All rights reserved.
File name : array.cpp
Version : v1.0
Author : zhengqijun
Date : 2018-08-10
Function List :
Description : array container.
******************************************************/
#include <iostream>
#include <array>
#include <tuple>
int main(void) {
std::array<int,3> myarray = {10, 20, 30};
std::tuple<int, int, int> mytuple (10, 20, 30);
std::tuple_element<0, decltype(myarray)>::type myelement; // int myelement
myelement = std::get<2>(myarray);
std::get<2>(myarray) = std::get<0>(myarray);
std::get<0>(myarray) = myelement;
std::cout << "first element in myarray: " << std::get<0>(myarray) << std::endl;
std::cout << "first element in mytuple: " << std::get<0>(mytuple) << std::endl;
return 0;
}
執行結果如下所示:
first element in myarray: 30
first element in mytuple: 10
建議:多使用array陣列容器代替c型別陣列,使運算元組元素更加安全!