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Q3: What member functions does vector contain?
| member function | function function |
|---|---|
| begin() | Returns an iterator pointing to the first element in the container |
| end() | Returns an iterator pointing to the position after the last element of the container, usually used in conjunction with begin() |
| size() | returns the actual number of elements |
| resize() | Change the number of actual elements |
| empty() | Determine whether there is an element in the container, if there is no element, return true; otherwise, return false |
| insert() | Insert one or more elements at the specified position |
| erase() | remove an element or a block of elements |
| clear() | Remove all elements, container size becomes 0 |
| swap() | swaps all elements of two containers |
| push_back() | Add an element to the end of the sequence |
| pop_back() | removes elements from the end of the sequence |
Note: The vector container contains many member functions, only some of them are listed here
1.push_back() and pop_back functions
vector v1={
1,2,3,4,5};
v1.push_back(6);//在末尾添加6
for (int i = 0; i < v1.size(); ++i) {
cout<<v1.at(i)<<' ';
}
**结果：1 2 3 4 5 6
vector v1={
1,2,3,4,5};
v1.pop_back();//不需要参数
for (int i = 0; i < v1.size(); ++i) {
cout<<v1.at(i)<<' ';
}
**结果·：1 2 3 4
2.swap() exchange function
The swap function can be used to exchange the content of two vector containers , see the example:
int a[5]={
1,2,3,4,5};
vector<int> v1,v2;
v1.assign(a,a+5); //初始化v1={1,2,3,4,5}
v2.assign(3,6); //初始化v2={6,6,6}
v1.swap(v2); //swap()实现vector容器交换
//以下为输出容器元素，检测结果
for (int i = 0; i < v1.size(); ++i) {
cout<<v1[i]<<' ';
}
cout<<endl;
for (int i = 0; i < v2.size(); ++i) {
cout<<v2[i]<<' ';
}
cout<<endl;
**结果：6 6 6
1 2 3 4 5
//实现了交换
3.insert() insert function
- The easiest way to insert data at a specified location is
v.insert(pos,x);herePointer for position posTo determine, x is the data to be inserted, and there are other insertion forms, see examples:
vector<int> v1, v2;
v1 = {
1, 2, 3, 4, 5};
//指定位置插入元素
v1.insert(v1.begin() + 2, 100);//第一个元素为指针
for (int i = 0; i < v1.size(); ++i) {
cout << v1.at(i) << ' ';
}
cout << endl;
//**结果：1 2 100 3 4 5 //指针指向的位置变成指定数据，后面的元素依次后移
//指定位置插入多个元素
v1.insert(v1.begin(), 3, 99);
for (int i = 0; i < v1.size(); ++i) {
cout << v1.at(i) << ' ';
}
cout << endl;
//**结果：99 99 99 1 2 100 3 4 5
//指定位置插入区间数据
v2 = {
1, 2, 3, 4, 5};
int b[5] = {
10, 20, 30, 40, 50};
v2.insert(v2.begin() + 1, b + 1, b + 3);
for (int i = 0; i < v2.size(); ++i) {
cout << v2.at(i) << ' ';
}
cout << endl;
//**结果：1 20 30 2 3 4 5
4.empty() judgment empty function
vector<int> v1, v2;
v1 = {
1, 2, 3, 4, 5};
cout << "v1=" << v1.empty() << endl;
cout << "v2=" << v2.empty() << endl;
**结果：v1=0//代表空
v2=1
5.resize() to change the container length function
- Reduce the length, if there is an element in the reduced position, the element will be deleted
vector<int> v1; //如果长度缩小，会将后面的元素删除
v1 = {
1, 2, 3, 4, 5};
v1.resize(3);
for (int i = 0; i < v1.size(); ++i) {
cout << v1[i] << ' ';
**结果：1 2 3 //原本是5个元素，当长度减小为3，原本后面的元素就被删除了
}
- increase the length
vector<int> v1, v2;
int a[5] = {
1, 2, 3, 4, 5};
v2.assign(a, a + 5);
v2.resize(8); //传入的参数要大于原来的容器长度
for (int i = 0; i < v2.size(); ++i) {
cout << v2[i] << ' ';
}
cout << endl;
//结果：1 2 3 4 5 0 0 0 //增加的位置会自动补0
You can also specify the value of the extended area
vector<int> v1, v2;
int a[5] = {
1, 2, 3, 4, 5};
v2.assign(a, a + 5);
v2.resize(8,10); //第一个参数为要扩展的长度，第二个参数为指定数值
for (int i = 0; i < v2.size(); ++i) {
cout << v2[i] << ' ';
}
cout << endl;
**结果：1 2 3 4 5 10 10 10
6.erase() delete function
vector<int> v1, v2;
v1 = {
1, 2, 3, 4, 5};
v1.erase(v1.begin() + 2);//注意传入的是指向要删除数据的指针！
for (int i = 0; i < v1.size(); ++i) {
cout << v1.at(i) << ' ';
}
cout << endl;
//**结果：1 2 4 5
7.clear() clear function
vector<int> v1, v2;
v1 = {
1, 2, 3, 4, 5};
v1.clear();
cout << v1.empty();
cout << endl;
//结果：1 代表容器v1为空