vector类的介绍（构造， 访问及遍历， 容量操作及空间增长问题， 增删改查， 迭代器失效场景）

vector类

vector类简介

1、vector表示变长数组的序列容器
2、vector类采用连续空间存储，大小可变，可以对元素像数组一样下标访问
3、vector使用动态分配数组来存储它的元素
4、vector在访问元素的时候更加高效，尾插尾删的效率高效。

1、vector类的构造

(constructor)构造函数声明	接口说明
vector()	无参构造
vector（size_type n, const value_type& val = value_type()）	构造并初始化n个val
vector (const vector& x);	拷贝构造
vector (InputIterator first, InputIterator last);	使用迭代器进行初始化构造

#include <iostream>
#include <vector>

using namespace std;

void TestVector()
{
	vector<int> first;
	vector<int> second(4, 100);
	vector<int> third(second.begin(), second.end());
	vector<int> fourth(third);

	int array[] = { 9, 5, 2, 7 };
	vector<int> fifth(array, array + sizeof(array) / sizeof(array[0]));
	for (vector<int>::iterator it = fifth.begin(); it != fifth.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;
}

int main()
{
	TestVector();
	system("pause");
	return 0;
}

2、vector类的访问及遍历

iterator的使用	接口说明
begin + end	获取第一个数据位置的iterator/const_iterator， 获取最后一个数据的下一个位置的iterator/const_iterator
rbegin + rend	获取最后一个数据位置的reverse_iterator，获取第一个数据前一个位置的

reverse_iterator

#include <iostream>
#include <vector>

using namespace std;

void PrintVector(const vector<int>& v)
{
	vector<int>::const_iterator it = v.begin();
	for (; it != v.end(); it++)
	{
		cout << *it << ' ';
	}
	cout << endl;
}

int main()
{
	vector<int> v;
	v.push_back(9);
	v.push_back(5);
	v.push_back(2);
	v.push_back(7);

	vector<int>::iterator it1 = v.begin();
	for (; it1 != v.end(); it1++)
	{
		cout <<  *it1 << ' ';
	}
	cout << endl;

	vector<int>::iterator it2 = v.begin();
	for (; it2 != v.end(); it2++)
	{
		*it2 *= 2;
		cout << *it2 << ' ';
	}
	cout << endl;

	vector<int>::reverse_iterator rit = v.rbegin();
	for (; rit != v.rend(); rit++)
	{
		cout << *rit << ' ';
	}
	cout << endl;

	PrintVector(v);

	system("pause");
	return 0;
}

3、vector类的容量操作及空间增长问题

容量空间	接口说明
size	获取数据个数
capacity	获取容量大小
empty	判断是否为空
resize	改变vector的size
reserve	改变vector放入capacity

#include <iostream>
#include <vector>

using namespace std;

void TestCapacity()
{
	size_t size;
	vector<int> foo;

	size = foo.capacity();
	cout << "making foo grow:" << endl;
	for (int i = 0; i < 100; i++)
	{
		foo.push_back(i);
		if (size != foo.capacity())
		{
			size = foo.capacity();
			cout << "capacity changed: " << size << endl;
		}
	}
}

void TestReserve()
{
	size_t size;
	vector<int> bar;
	
	size = bar.capacity();
	bar.reserve(100);
	
	cout << "making bar grow" << endl;
	for (int i = 0; i < 100; i++)
	{
		bar.push_back(i);
		if (size != bar.capacity())
		{
			size = bar.capacity();
			cout << "capacity changed: " << size << endl;
		}
	}
}

void TestResize()
{
	vector<int> v;
	for (int i = 0; i < 10; i++)
	{
		v.push_back(i);
	}

	v.resize(5);
	v.resize(8, 100);
	v.resize(12);

	cout << "v contains:" << endl;
	for (int i = 0; i < v.size(); i++)
	{
		cout << v[i] << ' ';
	}
	cout << endl;
}

int main()
{
	TestCapacity();
	TestReserve();
	TestResize();

	system("pause");
	return 0;
}

1、capacity在vs下按1.5倍增长，g++是按2倍增长
2、reserve负责开辟空间，预知空间大小，可以使用reserve缓解扩容缺陷
3、resize在开辟空间的同时会初始化，影响size

4、vector类的增删改查

vector增删查改	接口说明
push_back	尾插
pop_back	尾删
find	查找。（注意这个是算法模块实现，不是vector的成员接口）
insert	在position之前插入val
erase	删除position位置的数据
swap	交换两个vector的数据空间
operator[]	像数组一样访问

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

void TestPushAndPop()
{
	int a[] = { 1, 2, 3, 4 };
	vector<int> v(a, a + sizeof(a) / sizeof(a[0]));

	vector<int>::iterator it = v.begin();
	for (; it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;

	v.pop_back();
	v.pop_back();

	it = v.begin();
	for (; it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;
}

void TestFindInsertErase()
{
	int a[] = { 1, 2, 3, 4 };
	vector<int> v(a, a + sizeof(a) / sizeof(a[0]));

	vector<int>::iterator pos = find(v.begin(), v.end(), 3);

	v.insert(pos, 30);

	vector<int>::iterator it = v.begin();
	for (; it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;

	pos = find(v.begin(), v.end(), 3);

	v.erase(pos);

	it = v.begin();
	for (; it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;


}

void TestIndexVisit()
{
	int a[] = { 1, 2, 3, 4 };
	vector<int> v(a, a + sizeof(a) / sizeof(a[0]));

	v[0] = 10;
	cout << v[0] << endl;

	for (int i = 0; i < v.size(); i++)
	{
		cout << v[i] << ' ';
	}
	cout << endl;

	vector<int> tmp;
	tmp.swap(v);

	for (int i = 0; i < tmp.size(); i++)
	{
		cout << tmp[i] << ' ';
	}
	cout << endl;

	for (auto & e : v)
	{
		cout << e << ' ';
	}
	cout << endl;
}

int main()
{
	TestPushAndPop();
	TestFindInsertErase();
	TestIndexVisit();

	system("pause");
	return 0;
}

5、vector类的迭代器失效场景

#include <iostream>
#include <vector>

using namespace std;

void TestInsertErase()
{
	int a[] = { 1, 2, 3, 4 };
	vector<int> v(a, a + sizeof(a) / sizeof(a[0]));

	//删除导致迭代器非法访问的失效
	vector<int>::iterator pos = find(v.begin(), v.end(), 3);

	v.erase(pos);
	cout << *pos << endl;

	//插入导致增容，增容后pos指向新的空间，原来的空间已经被释放
	pos = find(v.begin(), v.end(), 3);

	v.insert(pos, 30);
	cout << *pos << endl;
}

void TestVector()
{
	int a[] = { 1, 2, 3, 4 };
	vector<int> v(a, a + sizeof(a) / sizeof(a[0]));

	vector<int>::iterator it = v.begin();
	while (it != v.end())
	{
		if (*it % 2 == 0)
		{
			it = v.erase(it);
		}
		else
		{
			it++;
		}
	}
	cout << endl;

	//失效
	/*it = v.begin();
	for (; it != v.end(); it++)
	{
		if (*it % 2 == 0)
		{
			v.erase(it);
		}
	}
	cout << endl;*/


}

int main()
{
	//TestInsertErase();
	TestVector();

	system("pause");
	return 0;
}

迭代器失效场景：

1、删除导致迭代器非法访问的失效
2、插入导致增容，增容后pos指向新的空间，原来的空间已经被释放