c++知识

函数模板：

template<class TT>
void Tswap(TT &t1,TT &t2){
	TT t = t1;
	t1 = t2;
	t2 = t;
}

具体化函数模板：

struct people{
	string name;
	int age;
};
template<>void Tswap<people>(people &p1,people &p2){
	int age = p1.age;
	p1.age = p2.age;
	p2.age = age;
}

实例化函数模板：

template<class T>
void Tswap(T &t1,T &t2,T &t3){
	cout<<"22223333"<<endl;
}

//这里的函数定义相当于是对上面函数的实例化，所以叫实例化函数模板
template void Tswap<people>(people &p1,people &p2,people &p3);

类模板：

template<class TTT>
class TestPeople{
public:
	TestPeople(TTT &p1,TTT &p2){
		cout<<"construct"<<endl;
	}
};
int main(){
	people p1 = {"mick",21};
	people p2 = {"jick",31};
	people p3 = {"tom",35};
	TestPeople<people> p(p1,2);
	getchar();
	return 0;
}

复制构造函数：
系统会默认为类创建一个复制构造函数，把成员变量复制到新的对象中：

template<class TTT>
class TestPeople{
public:
	TestPeople(TTT &p1,TTT &p2){
		cout<<"construct"<<endl;
		t1 = &p1;
		t2 = &p2;
	}
	TestPeople(TestPeople &tp){
		cout<<"复制构造函数"<<endl;
	}
	TTT *t1;
	TTT *t2;
};
int main(){
	people p1 = {"mick",21};
	people p2 = {"jick",31};
	people p3 = {"tom",35};
	//创建一个对象
	TestPeople<people> *p = new TestPeople<people>(p1,p2);
	//调用复制构造函数，好像只能通过指针来调用复制构造函数
	TestPeople<people> t = (*p);
	p1.name = "test";
	cout<<p->t1->name<<endl;
	cout<<t.t1->name<<endl;
	getchar();
	return 0;
}

按值传递会自动调用复制构造函数复制一个对象返回：

class TestOperator{
private:
	int n;
public:
	TestOperator(int x):n(x){
		cout<<"构造函数"<<endl;
	}
	int get(){
		return n;
	}
	//重载了复制构造函数
	TestOperator(TestOperator &t){
		cout<<"copy con"<<endl;
	}		
	//这里按值返回了一个TestOperator的对象，会调用上面的复制构造函数
	TestOperator operator++(){
		++n;
		cout<<"++运算符"<<endl;
		return *this;
	}
};

运算符重载：

class TestOperator{
private:
	int n;
public:
	TestOperator(int x):n(x){
		cout<<"构造函数"<<endl;
	}
	int get(){
		return n;
	}
	TestOperator(TestOperator &t){
		cout<<"copy con"<<endl;
	}
	//重载了++运算符
	TestOperator operator++(){
		++n;
		cout<<"++运算符"<<endl;
		return *this;
	}
	//重载=运算符
	void operator=(TestOperator &a){
		this->n = a.get();
	}
	//将对象转换为基本类型
	operator int(){
		return n;
	}
};
int main(){
	TestOperator t(2);
	TestOperator tt(3);
	//调用=重载运算符
	tt = t;
	cout<<tt.get()<<endl;
	//调用operator int()
	int i = tt;
	cout<<i<<endl;
	//这里的调用顺序：调用构造函数，将i传递进去，创建了一个临时对象，然后调用=运算符，将临时对象赋值给ttt
	TestOperator ttt = i;
	getchar();
	return 0;	
}

预处理指令中可以使用#运算符，#运算符把其后的任何字符用""引起来
#define show(x) cout<<#x
show(hello world)将输出hello world

##将多个字符串连接成一个字符串
#define show(x) cout<<"show "##x##" student"
show(one) 输出show one student

#if defined 判断某个宏是否已被定义,#是其缩写形式#ifdef，#if !defined的缩写形式是#ifndef

#pragma：
#pragma message("")编译时输出信息
#pragma once 编译时只编译一次