C++ vector添加对象方式

文章目录

  • 1 行为方式
  • 2 vector添加对象方式1
    • 2.1 示例
    • 2.2 运行
  • 3 vector添加对象方式2(指定容量)
    • 3.1 示例
    • 3.2 运行

1 行为方式

1、Vector每添加一个对象,就会进行一轮调用拷贝构造函数创建新对象;
2、若添加对象时容量不足
(1)先通过拷贝构造出来创建新对象;
(2)进行扩容迁移原先的对象;
(3)添加(1)步骤中创建的新对象;
3、若vector初始化时未指定capacity容量,则每添加一个对象,容量与元素个数从0开始依次增加1;

2 vector添加对象方式1

2.1 示例

#include 
#include 
#include 
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 运行

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

备注:
Vector初始化后
C++ vector添加对象方式_第1张图片
添加a1后
C++ vector添加对象方式_第2张图片
添加a2后
C++ vector添加对象方式_第3张图片
添加a3后
在这里插入图片描述

3 vector添加对象方式2(指定容量)

3.1 示例

#include 
#include 
#include 
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 运行

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

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