【C++STL】《别再踩坑！vector 用不对还崩代码？这篇帮你避掉 90% 的坑》

#include<vector>
#include<iostream>
using namespace std;
int main()
{
	//默认构造
	vector<int> v1;
	//使用n个值构造初始化
	vector<int> v2(10, 1);//用10个1初始化v2
	for (auto e : v2)
	{
		cout << e<< " ";
	}
	cout << endl;
	//拷贝构造
	vector<int> v3(v2);//v2拷贝给v3
	for (auto e : v3)
	{
		cout << e << " ";
	}
	cout << endl;
	//使用迭代器初始化
	vector<int>::iterator it = v2.begin();
	vector<int> v4(v2.begin(), v2.end());
	for (auto e : v4)
	{
		cout << e << " ";
	}
	return 0;

}

int main()
{
	//初始化列表初始化就是像数组一样使用花括号初始化
	int a[] = { 10, 20, 30 };
	auto il1 = { 10, 20, 30 };
	auto il2 = { 10, 20, 30,1,1,1,1,1,1,1 };
	cout << typeid(il1).name() << endl;//使用typeid查看真实的类型是			initializer_list
	//cout << il1.begin() << endl; li1与a(整型)的地址相似说明它们类型是一样的
	//cout << a << endl;

	vector<int> v1 = { 10, 20, 30 };
	vector<int> v2 = { 10, 20, 30,1,1,1,1,1,1,1 };
	for (const auto& e : v1)
	{
		cout << e << " ";
	}
	cout << endl;
}

#include<vector>
#include<iostream>
using namespace std;
int main()
{
	vector<int> v1 = { 1, 2, 3 };
	//正向迭代器
	vector<int>::iterator it1 = v1.begin();
	while (it1 != v1.end())
	{
		cout << *it1<<" ";
		++it1;
	}
	cout << endl;
	//反向迭代器
	vector<int>::reverse_iterator it2 = v1.rbegin();
	while (it2 != v1.rend())
	{
		cout << *it2<<" ";
		++it2;
	}
	cout << endl;
	//范围for （推荐）
	for (auto e : v1)
	{
		cout << e <<" ";
	}
}

#include<vector>
#include<iostream>
using namespace std;
int main()
{
	vector<int> v1(10, 11);
	//有效数据个数
	cout << v1.size() << endl;
	//空间大小
	cout << v1.capacity() << endl;

	if (!v1.empty())//判断vector是否为空
	{
		for (auto e : v1)
		{
			cout << e << " ";
		}
	}
	cout << endl;
	//扩容 扩容的空间使用6来填充
	v1.resize(20, 6);
	cout <<"size:"<< v1.size() << endl;
	cout <<"capacity:"<< v1.capacity() << endl;
	for (auto e : v1)
	{
		cout << e << " ";
	}
	cout << endl;
	//resise缩容 
	v1.resize(5);//缩小的是有效数据个数
	cout << "size:" << v1.size() << endl;
	cout << "capacity:" << v1.capacity() << endl;
	
	vector<int> v2;
	v2.reserve(10);
	cout << "size:" << v2.size() << endl;
	cout << "capacity:" << v2.capacity() << endl;

	return 0;
}

#include<vector>
#include<iostream>
using namespace std;
int main()
{
	vector<int> v1;
	//尾插
	v1.push_back(1);
	v1.push_back(2);
	v1.push_back(3);
	cout << "size:" << v1.size() << endl;
	//删除数据
	v1.pop_back();
	cout << "size:" << v1.size() << endl;

	//insert 效率较低涉及数据的移动
	vector<int> v2;
	v2.push_back(1);
	v2.push_back(2);
	v2.push_back(3);
	v2.push_back(5);
	v2.insert(v2.begin() + 3, 100);
	//（算法库的）find+insert
	auto it = find(v2.begin(), v2.end(), 2);
	if (it != v2.end())
	{
		//在该迭代器位置处插入50
		v2.insert(it, 50);
	}

	//erase 效率较低涉及数据的移动
	v2.erase(v2.begin() + 3);//删除下标为3位置处的数据
	//find+erase
	auto it1 = find(v2.begin(), v2.end(), 100);
	if (it1 != v2.end())
	{
		v2.erase(it1);
	}
	//下标访问
	cout<<v2[5]<<endl;
	return 0;
	}

struct A
{
	A(int a1, int a2)
		:_a1(a1)
		,_a2(a2)
	{
		cout << "A(int a1, int a2)" << endl;
	}
	A(const A& aa)
		:_a1(aa._a1)
		,_a2(aa._a2)
	{
		cout << "A(const A& aa)" << endl;
	}
	int _a1;
	int _a2;
};
int main()
{
	//push_back与emplace_back效率的比较
	vector<A> v2;
	A aa1(1, 1);
	v2.push_back(aa1);
	cout << endl;
	v2.push_back(A(2,2));
	cout << endl;

	v2.push_back({3,3});
	cout << endl;

	cout << "**************************" << endl;

	v2.emplace_back(aa1);
	cout << endl;

	v2.emplace_back(A(2, 2));
	cout << endl;
	
	v2.emplace_back( 3,3 );
	//emplace_back不支持初始化列表初始化
	//v2.emplace_back({ 3,3 });

	//遍历自定义类型可以使用范围for也可以使用结构化绑定
	//C++11 范围for
	for (auto& aa : v2)
	{
		cout << aa._a1 << ":" << aa._a2 << endl;
	}

	// C++17 结构化绑定
	//auto [x, y] = aa1;//x y为A类型的成员变量 x y 的名字可以任取
	for (auto& [x, y] : v2)
	{
		cout << x << ":" << y << endl;
	}
}