vector容器、swap、reserve、resize

  1 #define _CRT_SECURE_NO_WARNINGS
  2 #include <iostream>
  3 #include <cstdlib>
  4 #include <vector>  //动态数组
  5 #include <algorithm>  //算法
  6 
  7 using namespace std;
  8 
  9 void print_vector(vector<int> &v) {
 10     for (vector<int>::iterator it = v.begin(); it != v.end(); it++) {
 11         cout << *it << " ";
 12     }
 13     cout << endl;
 14 }
 15 
 16 void test01() {
 17     vector<int> v1;//默认构造
 18     int arr[] = { 10,20,30,40 };
 19     vector<int> v2(arr, arr + sizeof(arr) / sizeof(int));
 20     vector<int> v3(v2.begin(), v2.end());
 21     vector<int> v4(v3);
 22 
 23     print_vector(v2);
 24     print_vector(v3);
 25     print_vector(v4);
 26 }
 27 
 28 void test02() {
 29     int arr[] = { 10,20,30,40 };
 30     vector<int> v1(arr, arr + sizeof(arr) / sizeof(int));
 31     vector<int> v2;
 32     v2.assign(v1.begin(), v1.end());
 33     vector<int> v3;
 34     v3 = v2;
 35 
 36     int arr1[] = { 100,200,300,400 };
 37     vector<int> v4(arr1, arr1 + sizeof(arr1) / sizeof(int));
 38 
 39     print_vector(v1);
 40     print_vector(v2);
 41     print_vector(v3);
 42     print_vector(v4);
 43 
 44     cout << "-----------------" << endl;
 45 
 46     v4.swap(v1);//指针交换，不是堆上的数据拷贝
 47     print_vector(v1);
 48     print_vector(v2);
 49     print_vector(v3);
 50     print_vector(v4);
 51 
 52 }
 53 
 54 void test03() {
 55     int arr[] = { 10,20,30,40 };
 56     vector<int> v1(arr, arr + sizeof(arr) / sizeof(int));
 57     
 58     if (v1.empty()) {
 59         cout << "为空" << endl;
 60     }
 61     else {
 62         cout << "不为空" << endl;
 63     }
 64     print_vector(v1);
 65     v1.resize(2);//传进的参数小于容器的size，会从后往前删除相应数量元素
 66     print_vector(v1);
 67     v1.resize(6, 1);//传进的参数大于容器的size，会用传进的第二个参数补全
 68     print_vector(v1);
 69 
 70     for (int i = 0; i < 10000; i++) {
 71         v1.push_back(i);
 72     }
 73     
 74     cout << "size:" << v1.size() << endl;//元素个数
 75     cout << "容量:" << v1.capacity() << endl;//容量
 76 
 77 }
 78 
 79 void test04() {
 80     int arr[] = { 100,200,300,400 };
 81     vector<int> v1(arr, arr + sizeof(arr) / sizeof(int));
 82     for (int i = 0; i < v1.size(); i++) {
 83         cout << v1[i] << " ";
 84     }
 85     cout << endl;
 86 
 87     for (int i = 0; i < v1.size(); i++) {
 88         cout << v1.at(i) << " ";
 89     }
 90     cout << endl;
 91     //at是抛异常的，[]不抛异常
 92 
 93     v1.push_back(10);
 94     v1.push_back(20);
 95     v1.insert(v1.begin(), 30);
 96     v1.insert(v1.end(), 40);
 97     v1.insert(v1.begin() + 2, 110);//vector支持迭代器随机访问
 98     //一般情况下，支持数组下标，都支持随机访问
 99 
100     print_vector(v1);
101 
102     //删除
103     v1.erase(v1.begin());
104     print_vector(v1);
105     v1.erase(v1.begin() + 1, v1.end());
106     print_vector(v1);
107     v1.clear();
108     
109     cout << "size:" << v1.size() << endl;
110 
111 
112 }
113 
114 //巧用swap缩减空间
115 void test05(){
116     //vector添加元素时会自动增长空间，但是删除元素时不会自动缩小空间
117     vector<int> v;
118     for (int i = 0; i < 100000; i++) {
119         v.push_back(i);
120     }
121     cout << "size:" << v.size() << endl;
122     cout << "capacity:" << v.capacity() << endl;
123 
124     v.resize(10);
125     cout << "-------------" << endl;
126     cout << "size:" << v.size() << endl;
127     cout << "capacity:" << v.capacity() << endl;
128 
129     //收缩空间
130     //vector<int>(v)这是一个用v初始化的匿名对象
131     //与v交换完指针后使v的空间压缩，匿名对象自动销毁
132     vector<int>(v).swap(v);
133     cout << "-------------" << endl;
134     cout << "size:" << v.size() << endl;
135     cout << "capacity:" << v.capacity() << endl;
136 }
137 
138 void test06() {
139     //reserve预留空间 与resize区别
140 
141     int num = 0;
142     int* address = NULL;
143 
144     vector<int> v;
145     v.reserve(100000);//预留空间
146     for (int i = 0; i < 100000; i++) {
147         v.push_back(i);
148         if (address != &(v[0])) {
149             address = &(v[0]);
150             num++;//可以判断扩展空间的次数
151         }
152     }
153     
154     cout << "num:" << num << endl;
155     //如果知道容器大概需要的存储空间的元素个数，那么可以用reserve预留空间
156     //避免多次扩展空间减低效率
157 }
158 
159 int main(void) {
160     test06();
161 
162     system("pause");
163     return 0;
164 }