变参模板、完美转发和emplace

1 变参模板、完美转发和emplace

变参模板：使得 emplace 可以接受任意参数，这样就可以适用于任意对象的构建。
完美转发 ：使得接收下来的参数能够原样的传递给对象的构造函数，这带来另一个方便性，避免构造临时对象，提高效率。

测试代码如下：

#include <iostream>
using namespace std;

#include <vector>
#include <list>
#include <deque>
#include <algorithm>


class student {
public:
	student() {
		cout << "无参构造函数被调用!" << endl;
	}

	student(int age, string name, int test) {
		this->age = age;
		//strncpy_s(this->name, name, 64);
		cout << "有参构造函数被调用!" << endl;
		cout << "姓名：" << name.c_str() << " 年龄：" << age << endl;
	}

	student(const student &s) {
		this->age = s.age;
		//strncpy_s(this->name, s.name, 64);

		cout << "拷贝构造函数被调用!" << endl;
	}

	~student() {
		cout << "析构函数被调用" << endl;
	}
public:
	int age;
	string name;
};


int main(void) {
	//vector<int>   vectInt(10);
	deque<int>   dqInt;    
	list<int>    lstInt; 
	vector<student>   vectStu(10);

	cout << "vectStu size:" << vectStu.size() << endl;
	cout << "vectStu capacity:" << vectStu.capacity() << endl;
	//插入学生

	//方法一  先定义对象，再插入
	//student  xiaoHua(18, "李校花");
	//vectStu.push_back(xiaoHua);

	//方法二  直接插入临时对象
	//vectStu.push_back(student(19, "王大锤"));

	//c++11 新特性: 变参模板和完美转发的表演啦

	vectStu.emplace_back(19, "王大锤", 11);   //push_back
	cout << "vectStu size (1):" << vectStu.size() << endl;
	cout << "vectStu capacity(1):" << vectStu.capacity() << endl;

	vectStu.emplace(vectStu.end(), 18, "lixiaohua", 12);   //相当于 insert.
	cout << "vectStu size (2):" << vectStu.size() << endl;
	cout << "vectStu capacity (2):" << vectStu.capacity() << endl;

	system("pause");
	return 0;
}

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参考资料：

1. C/C++从入门到精通-高级程序员之路【奇牛学院】