C++一些例子

---

虚析构

#include<iostream>
class Base
{
public:
	Base() { std::cout << "base 构造" << std::endl; }
	
	virtual~Base() { std::cout << "base 析构" << std::endl; }
};
class Derived : public Base
{
public:
	Derived() { std::cout << "derived 构造" << std::endl; }
	~Derived() { std::cout << "derived 析构" << std::endl; }
};

int main()
{
	Base* base = new Base();
	delete base;
	std::cout << "--------------" << std::endl;
	Derived* der = new Derived();
	delete der;
	std::cout << "--------------" << std::endl;
	Base* p = new Derived();
	delete p;
	std::cin.get();
}

---

联合体

#include<iostream>

struct Vector1
{
	float x, y;
};

struct Vector2
{
	union
	{
		struct 
		{
			float x, y, z, w;
		};
		struct 
		{
			Vector1 a, b;

		};
	};
};
void PrintVector(const Vector1& vector)
{
	std::cout << vector.x << " " << vector.y << std::endl;
}
int main()
{
	Vector2 vector = { 1.0f,2.0f,3.0f,4.0f };
	PrintVector(vector.a);
	PrintVector(vector.b);
	// 1 2 3 4
	vector.z = 100.0f;
	PrintVector(vector.a);
	PrintVector(vector.b);
	// 1 2 100 4
	std::cin.get();
}

---

线程

#include<iostream>
#include<thread>

static bool Finished = false;

void DoWorker()
{
	using namespace std::literals::chrono_literals;
	std::cout << "id: " << std::this_thread::get_id() << std::endl;
	while (!Finished)
	{
		std::cout << "Working...." << std::endl;
		std::this_thread::sleep_for(1s);
        //std::cin.get()
		
	}
}

int main()
{
	std::thread worker(DoWorker);
	std::cin.get();
	Finished = true;
	worker.join();

	std::cin.get();
}

---

预处理

#if _DEBUG==1
#define LOG(x) cout<<x<<endl
#elif(_RELESE)
#define LOG(x)
#endif

---

重载操作符

class Vector1
{
public:
	float x, y;
public:
	Vector1(float X, float Y)
		: x(X), y(Y) 
	{
		Vector1* const &e = this;
	}
	Vector1 Add(const Vector1& other)const
	{
		return Vector1(x + other.x, y + other.y);
	}
	Vector1 operator+(const Vector1& other)const
	{
		return Add(other);
	}
	Vector1 Multiply(const Vector1& other)const
	{
		return Vector1(x * other.x, y * other.y);
	}
	Vector1 operator*(const Vector1& other)const
	{
		return Multiply(other);
	}
	bool operator==(const Vector1& other)const
	{
		return x == other.x && y == other.y;
	}
	bool operator!=(const Vector1& other)const
	{
		return !(*this == other);
	}
};
std::ostream& operator<<(ostream& stream, const Vector1& other)
{
	stream << other.x << "," << other.y;
	return stream;
}
int main()
{
    Vector1 v1(1.1f, 2.2f);
	Vector1 v2(3.3f, 4.4f);
	Vector1 result1 = v1 + v2;	
	Vector1 result2 = v1 * v2;
	cout << result1 << endl;
	cout << result2 << endl;
	if (result1 != result2)
		cout << "==" << endl;
	else
		cout << "!=" << endl;
    
    cin.get();
}

---

智能指针

class Entity
{

};
{
		shared_ptr<Entity>weakEneity;
		{
			unique_ptr<Entity>entity = make_unique<Entity>();
			shared_ptr<Entity>sharedEntity = make_shared<Entity>();
			weakEneity = sharedEntity;
			entity->print();
		}
		 
	}

---

lambda

#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
using namespace std;

void Foreach(const vector<int>& v,const function<void(int)>&func)
{
	for (int i : v)
	{
		func(i);
	}
}
int main()
{
	vector<int>v = { 1,2,3,4 };
	auto it = find_if(v.begin(), v.end(), [](int val){ return val > 2; });
	cout << *it << endl;

	auto lambda = [=](int val) {cout << val << endl; };
	Foreach(v, lambda);
    cin.get();
}

---

函数指针

void Println(int val)
{
	cout << val << endl;
}

void Foreach(const vector<int>& v,void(*func)(int val))
{
	for (int i : v)
	{
		func(i);
	}
}
int main()
{
	vector<int>v = { 1,2,3,4 };
	Foreach(v, Println);
}

void Foreach(const vector<int>& v,void(*func)(int val))
{
	for (int i : v)
	{
		func(i);
	}
}
int main()
{
	vector<int>v = { 1,2,3,4 };
	Foreach(v, [](int val) 
    {
        cout << val << endl; 
    });
}

---

使用箭头运算符，来获取内存中某个值的偏移量

#include<iostream>
using namespace std;

struct Vector
{
	int x, y, z;
};

int main()
{
	int offset = (int)&((Vector*)nullptr)->x;	
	//x,y,z 执行结果分别是0，4，8
	cout << offset << endl;
}

---

在不知道数组大小传递

template<int N>
void Array(const array<int,N>& arr)
{
	for (int i = 0; i < arr.size(); i++)
	{
		cout << arr[i];
	}
}
int main()
{
	array<int, 10>arr = { 1,1,1,1,1 };
	Array(arr);
}