STL——容器（List）list 的大小操作

ist.size();

//返回容器中元素的个数

 1 #include <iostream>
 2 #include <list>
 3
 4 using namespace std;
 5
 6 int main()
 7 {
 8     int num[] = { 111,222,333,444,555 };
 9     list<int> listInt_A(num, num + size(num));
10
11     cout << "容器中的元素数量为：" << listInt_A.size() << endl;
12
13     return 0;
14 }

打印结果：

list.empty();

//判断容器是否为空

 1 #include <iostream>
 2 #include <list>
 3
 4 using namespace std;
 5
 6 int main()
 7 {
 8     int num[] = { 111,222,333,444,555 };
 9     list<int> listInt_A(num, num + size(num));
10     list<int> listInt_B;
11
12     if (listInt_A.empty())                //如果不为空将会返回false，如果为空返回 ture
13     {
14         cout << "listInt_A 容器为空" << endl;
15     }
16     else
17     {
18         cout << "listInt_A 容器不为空" << endl;
19     }
20
21     if (listInt_B.empty())                //如果不为空将会返回false，如果为空返回 ture
22     {
23         cout << "listInt_B 容器为空" << endl;
24     }
25     else
26     {
27         cout << "listInt_B 容器不为空" << endl;
28     }
29
30     return 0;
31 }

打印结果：

list.resize(num);

//重新指定容器的长度为num，若容器变长，则以默认值0填充新位置。如果容器变短，则末尾超出容器长度的元素被删除

 1 #include <iostream>
 2 #include <list>
 3
 4 using namespace std;
 5
 6 int main()
 7 {
 8     int num[] = { 111,222,333,444,555 };
 9     list<int> listInt_A(num, num + size(num));
10
11     cout << "resize 前遍历 listInt_A：" << endl;
12     for (list<int>::iterator it = listInt_A.begin(); it != listInt_A.end(); it++)
13     {
14         cout << *it << " ";
15     }
16     cout << endl;
17
18     //使用 resize 重新指定容器长度
19     listInt_A.resize(9);
20     cout << "resize 扩充至9个元素后遍历 listInt_A：" << endl;
21     for (list<int>::iterator it = listInt_A.begin(); it != listInt_A.end(); it++)
22     {
23         cout << *it << " ";
24     }
25     cout << endl;
26
27     //使用 resize 重新指定容器长度
28     listInt_A.resize(3);
29     cout << "resize 删减至3个元素后遍历 listInt_A：" << endl;
30     for (list<int>::iterator it = listInt_A.begin(); it != listInt_A.end(); it++)
31     {
32         cout << *it << " ";
33     }
34     cout << endl;
35
36     return 0;
37 }

打印结果：

list.resize(num, elem);

//重新指定容器的长度为num，若容器变长，则以elem值填充新位置。如果容器变短，则末尾超出容器长度的元素被删除

 1 #include <iostream>
 2 #include <list>
 3
 4 using namespace std;
 5
 6 int main()
 7 {
 8     int num[] = { 111,222,333,444,555 };
 9     list<int> listInt_A(num, num + size(num));
10
11     cout << "resize 前遍历 listInt_A：" << endl;
12     for (list<int>::iterator it = listInt_A.begin(); it != listInt_A.end(); it++)
13     {
14         cout << *it << " ";
15     }
16     cout << endl;
17
18     //使用 resize 重新指定容器长度
19     listInt_A.resize(9, 888);
20     cout << "resize 扩充至9个元素后遍历 listInt_A：" << endl;
21     for (list<int>::iterator it = listInt_A.begin(); it != listInt_A.end(); it++)
22     {
23         cout << *it << " ";
24     }
25     cout << endl;
26
27     //使用 resize 重新指定容器长度
28     listInt_A.resize(3);
29     cout << "resize 删减至3个元素后遍历 listInt_A：" << endl;
30     for (list<int>::iterator it = listInt_A.begin(); it != listInt_A.end(); it++)
31     {
32         cout << *it << " ";
33     }
34     cout << endl;
35
36     return 0;
37 }

打印结果：

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