1 Behavior

1. Every time an object is added to the Vector, a round of calling the copy constructor will be performed to create a new object;
2. If the capacity is insufficient when the object is added
(1) Create a new object through copy construction first;
(2) Perform expansion and migration of the original object ;
(3) Add the new object created in step (1);
3. If the capacity is not specified when the vector is initialized, each time an object is added, the capacity and the number of elements will increase by 1 from 0;

2 Vector method of adding objects 1

2.1 Example

#include <iostream>
#include <string>
#include <vector>
using namespace std;

class A
{
    
    
private:
	int value;
public:
	A() {
    
     value = 0;cout << "A() this= " << this << ",value="<<value<<endl; }
	A(const A& a) {
    
    
		cout << "A(A&) this= " << this  << endl;
		this->value = a.value;
	}
	void setValue(int value) {
    
     this->value = value; }
	int getValue() {
    
     return this->value; }
};

int main()
{
    
     
	vector<A>  v;
	cout << endl << "start create object of A:" << endl;
	A a1, a2, a3;
	a1.setValue(1);
	a2.setValue(2);
	a3.setValue(3);
	cout << endl << "start push:" << endl;
	cout << endl << "start push a1:" << endl;
	v.push_back(a1);
	cout << endl << "start push a2:" << endl;
	v.push_back(a2);
	cout << endl << "start push a3:" << endl;
	v.push_back(a3);
	cout << endl<<"start setValue:" << endl;
	a1.setValue(4);
	a2.setValue(5);
	a3.setValue(6);

	cout << endl << "start for:" << endl;
	for (auto & a : v)
	{
    
    
		cout << &a << ",value="<<a.getValue()<<endl;
	}
}

2.2 Operation

start create object of A:
A() this= 00AFFDE8,value=0
A() this= 00AFFDDC,value=0
A() this= 00AFFDD0,value=0

start push:

start push a1:
A(A&) this= 00C160E8

start push a2:
A(A&) this= 00C1B46C
A(A&) this= 00C1B468

start push a3:
A(A&) this= 00C1B4A8
A(A&) this= 00C1B4A0
A(A&) this= 00C1B4A4

start setValue:

start for:
00C1B4A0,value=1
00C1B4A4,value=2
00C1B4A8,value=3

Remarks: After
Vector is initialized, after
Insert picture description here
adding a1, after

adding a2, after

adding a3

3 Vector adding object method 2 (specified capacity)

3.1 Example

#include <iostream>
#include <string>
#include <vector>
using namespace std;

class A
{
    
    
private:
	int value;
public:
	A() {
    
     value = 0;cout << "A() this= " << this << ",value="<<value<<endl; }
	A(const A& a) {
    
    
		cout << "A(A&) this= " << this  << endl;
		this->value = a.value;
	}
	void setValue(int value) {
    
     this->value = value; }
	int getValue() {
    
     return this->value; }
};

int main()
{
    
     
	vector<A>  v;
	v.reserve(5);
	cout << endl << "start create object of A:" << endl;
	A a1, a2, a3;
	a1.setValue(1);
	a2.setValue(2);
	a3.setValue(3);
	cout << endl << "start push:" << endl;
	cout << endl << "start push a1:" << endl;
	v.push_back(a1);
	cout << endl << "start push a2:" << endl;
	v.push_back(a2);
	cout << endl << "start push a3:" << endl;
	v.push_back(a3);
	cout << endl<<"start setValue:" << endl;
	a1.setValue(4);
	a2.setValue(5);
	a3.setValue(6);

	cout << endl << "start for:" << endl;
	for (auto & a : v)
	{
    
    
		cout << &a << ",value="<<a.getValue()<<endl;
	}
}

3.2 Operation

start create object of A:
A() this= 00EFF840,value=0
A() this= 00EFF834,value=0
A() this= 00EFF828,value=0

start push:

start push a1:
A(A&) this= 011B60E8

start push a2:
A(A&) this= 011B60EC

start push a3:
A(A&) this= 011B60F0

start setValue:

start for:
011B60E8,value=1
011B60EC,value=2
011B60F0,value=3

C++ vector add object method

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