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🍉本篇简介:>:介绍vector的使用

vector官网链接:传送门

一、构造函数

构造函数	含义
vector (const allocator_type& alloc = allocator_type());	无参构造
vector（size_type n, const value_type& val = value_type()）	初始化为n个val
vector (InputIterator first, InputIterator last,const allocator_type& alloc = allocator_type())	迭代器区间初始化
vector (const vector& x);	拷贝构造

(1)无参构造

默认什么元素也没有.
有效元素个数:size=0
容量:capacity=0;

	//无参构造
	vector<int> v1;
	//auto it1 = v1.begin();//可以使用auto自动推导类型
	vector<int>::iterator it1 = v1.begin();
	while (it1 != v1.end())
	{
		cout << *it1 << " ";
		it1 ++ ;
	}
	cout << "v1.size=" << v1.size() << endl;
	cout << "v1.capacity=" << v1.capacity() << endl;
	cout << endl;

运行结果:

v1.size=0
v1.capacity=0

(2)初始化为n个值

用n个val去初始化vector;

	//初始化为n个值
	vector<int> v2(4,0);
	//auto it2 = v2.begin();
	vector<int>::iterator it2 = v2.begin();
	while (it2 != v2.end())
	{
		cout << *it2 << " ";
		it2++;
	}
	cout << endl;

运行结果:

0 0 0 0

(3) 迭代器区间初始化

用一个迭代器区间进行初始化,这里采用数组的头和尾作为迭代器区间.

	//迭代器区间初始化
	int a3[10] = { 1,3,4,5,6,7,8,98,100,11 };
	vector<int> v3(a3, a3 + 10);//注意这里给的是+10,因为迭代器的end是指向最后一个有效元素的下一个位置,左闭右开
	auto it3 = v3.begin();
	while (it3 != v3.end())
	{
		cout << *it3 << " ";
		it3++;
	}
	cout << endl;

运行结果:

1 3 4 5 6 7 8 98 100 11

(4)拷贝构造

	//拷贝构造
	vector<int> v4(v3);//v3就是上面的迭代器区间初始化好的v3
	auto it4 = v4.begin();
	while (it4 != v4.end())
	{
		cout << *it4 << " ";
		it4++;
	}
	cout << endl;

运行结果:

1 3 4 5 6 7 8 98 100 11

二、容量操作

(1) 一览表

接口	说明
size()	有效数据的个数
resize()	改变有效数据的个数
capacity()	容量大小
empty()	判空
reserve()	改变容量大小

(2) 代码演示

void test2()
{
	int a1[10] = { 1,3,4,5,6,7,8,98,100,11 };
	vector<int> v1(a1, a1 + 10);
	cout << "v1.size()=" << v1.size() << endl;//显示有效数据的个数
	cout << "v1.capacity()=" << v1.capacity() << endl;//显示容量的大小
	cout << "v1.empty()=" << v1.empty() << endl;//判断容器是否为NULL
	cout << endl;


	v1.resize(5);//改变有效数据的个数
	cout << "v1.size()=" << v1.size() << endl;
	cout << "v1.capacity()=" << v1.capacity() << endl;
	vector<int>::iterator it1 = v1.begin();
	while (it1 != v1.end())
	{
		cout << *it1 << " ";
		it1++;
	}
	cout << endl;

	v1.resize(15,66);
	cout << "v1.size()=" << v1.size() << endl;
	cout << "v1.capacity()=" << v1.capacity() << endl;
	cout << endl;
	it1 = v1.begin();
	while (it1 != v1.end())
	{
		cout << *it1 << " ";
		it1++;
	}
	cout << endl;


	v1.reserve(10);//改变容量的大小.
	cout << "v1.capacity()=" << v1.capacity() << endl;
	v1.reserve(50);
	cout << "v1.capacity()=" << v1.capacity() << endl;

}

运行结果:

三、修改与访问

接口	说明
assign()	将新内容覆盖给容器，替换其当前内容，并相应地修改其大小。
push_back()	尾插
pop_back()	尾删
insert()	指定位置pos之前插入
erase()	删除指定位置pos的值
swap()	交换两个容器
operator[ ]()	下标访问运算符重载

(1) push_back && pop_back

尾插和尾删相信大家已经比较熟悉了.

assign()

assign函数需要注意.
void assign (size_type n, const value_type& val);

如果n<size,则是将n个val将原有数据覆盖,令size=n,而不修改容量.
如果n>size,则先扩容,再将n个val值存入.

	//push_back &&pop_back
	int a1[5] = { 1,2,3,4,5 };
	vector<int> v1(a1, a1 + 5);
	for (auto itt : v1){	//1 2 3 4 5
		cout << itt << " ";
	}
	cout << endl;
	
	//尾插
	v1.push_back(6);
	v1.push_back(7);
	for (auto itt : v1){	//1 2 3 4 5 6 7
		cout << itt << " ";
	}
	cout << endl;

	//尾删
	v1.pop_back();
	for (auto itt : v1){	//1 2 3 4 5 6
		cout << itt<<" ";
	}
	cout << endl;
	
	//将新内容覆盖给容器，替换其当前内容，并相应地修改其大小
	v1.assign(5, 2);
	for (auto itt : v1){	//2 2 2 2 2
		cout << itt << " ";
	}
	cout << endl << v1.size() << " " << v1.capacity() << endl;//5 7
	cout << endl;

运行结果:

1 2 3 4 5
1 2 3 4 5 6 7
1 2 3 4 5 6
2 2 2 2 2
5 7

(2) insert()

指定位置pos之前插入.

代码演示:

	int a1[5] = { 1,2,3,4,5 };
	vector<int> v1(a1, a1 + 5);
	for (auto itt : v1){
		cout << itt << " ";
	}
	cout << endl;
	//iterator insert(iterator position, const value_type & val);
	v1.insert(v1.begin() + 2, 66);//在第三个位置的前面插入数据.
	for (auto itt : v1)
	{
		cout << itt<<" ";
	}
	cout << endl;

	//void insert(iterator position, size_type n, const value_type & val);
	v1.insert(v1.begin() + 5, 5, -1);//在第六个位置的前面插入5个-1.
	for (auto itt : v1)
	{
		cout << itt << " ";
	}
	cout << endl;


	int a2[5] = { 1,2,3,4,5 };
	int a3[5] = { 6,7,8,9,10 };
	vector<int> v2(a2, a2 + 5);
	for (auto itt : v2)
	{
		cout << itt << " ";
	}
	cout << endl;

	//void insert (iterator position, InputIterator first, InputIterator last);
	v2.insert(v2.begin()+5,a3 ,a3 + 5);
	for (auto itt : v2)
	{
		cout << itt << " ";
	}
	cout << endl;

运行结果:

(3) erase()函数

删除指定位置pos的值

	//erase
	int a4[10] = { 1,2,3,4,5,6,7,8,9,10 };
	vector<int> v4(a4, a4 + 10);
	for (auto itt : v4)
	{
		cout << itt << " ";
	}
	cout << endl;

	//iterator erase (iterator position);
	v4.erase(v4.begin() + 1);
	for (auto itt : v4)
	{
		cout << itt << " ";
	}
	cout << endl;

	//iterator erase (iterator first, iterator last);
	v4.erase(v4.begin()+4, v4.begin() + 9);
	for (auto itt : v4)
	{
		cout << itt << " ";
	}
	cout << endl;

运行结果:

(4) swap()

用于交换两个容器,注意观察交换后容量的变化.

//swap
	//void swap(vector & x);
	int a5[10] = { 1,2,3,4,5,6,7,8,9,10 };
	vector<int> v5(a5, a5 + 10);
	int a6[10] = { 2,4,6,8,10 };
	vector<int> v6(a6, a6+5);
	
	cout << "v5=";
	for (auto itt : v5){
		cout << itt << " ";
	}
	cout << endl;

	cout << "v6=";
	for (auto itt : v6){
		cout << itt << " ";
	}
	cout << endl;

	swap(v5, v6);
	cout << endl;

	cout << "v5=";
	for (auto itt : v5){
		cout << itt << " ";
	}
	cout << endl;

	cout << "v6=";
	for (auto itt : v6){
		cout << itt << " ";
	}
	cout << endl;
	cout << "v5.capacity()" << v5.capacity();
	cout << endl;
	cout << "v6.capacity()" << v6.capacity();
	cout << endl;

运行结果:

(5) []运算符重载

可以像数组一样通过下标直接访问.

	//[]
	int a7[10] = { 1,2,3,4,5,6,7,8,9,10 };
	vector<int> v7(a5, a5 + 10);
	cout << "v7=";
	for (int i = 0; i < 10; i++)
	{
		cout << v7[i] << " ";
	}

v7=1 2 3 4 5 6 7 8 9 10

vector的使用就分享到这里了.下一期vector模拟实现见.