C++隐式构造

C++中存在隐式构造的现象：某些情况下，会隐式调用单参数的构造函数。

可以通过关键字 explicit 禁止掉隐式构造。

#include 
using namespace std;

class Person {
	int m_age;
public:
	Person() {
		cout << "Person() - " << this << endl;
	}
	Person(int age) :m_age(age) {
		cout << "Person(int) - " << this << endl;
	}
	Person(const Person &person) {
		cout << "Person(const Person &person) - " << this << endl;
	}
	~Person() {
		cout << "~Person() - " << this << endl;
	}
	void display() {
		cout << "display() - age is " << m_age << endl;
	}
};

int main() {

	Person p1 = 20; // 等价于 Person p1(20);

	getchar();
	return 0;
}

#include 
using namespace std;

class Person {
	int m_age;
public:
	Person() {
		cout << "Person() - " << this << endl;
	}
	Person(int age) :m_age(age) {
		cout << "Person(int) - " << this << endl;
	}
	Person(const Person &person) {
		cout << "Person(const Person &person) - " << this << endl;
	}
	~Person() {
		cout << "~Person() - " << this << endl;
	}
	void display() {
		cout << "display() - age is " << m_age << endl;
	}
};

//void test1(Person person) {
//
//}
//
//Person test2() {
//	return 40;
//}

int main() {
	//test1(30);
	//test2();

	//Person p1 = 20; // 等价于 Person p1(20);

	Person p1;
	p1 = 40;

	getchar();
	return 0;
}

#include 
using namespace std;

class Person {
	int m_age;
public:
	Person() {
		cout << "Person() - " << this << endl;
	}
	Person(int age) :m_age(age) {
		cout << "Person(int) - " << this << endl;
	}
	Person(const Person &person) {
		cout << "Person(const Person &person) - " << this << endl;
	}
	~Person() {
		cout << "~Person() - " << this << endl;
	}
	void display() {
		cout << "display() - age is " << m_age << endl;
	}
};

void test1(Person person) {

}

//
//Person test2() {
//	return 40;
//}

int main() {

	test1(30);
	//test2();

	getchar();
	return 0;
}

#include 
using namespace std;

class Person {
	int m_age;
public:
	Person() {
		cout << "Person() - " << this << endl;
	}
	Person(int age) :m_age(age) {
		cout << "Person(int) - " << this << endl;
	}
	Person(const Person &person) {
		cout << "Person(const Person &person) - " << this << endl;
	}
	~Person() {
		cout << "~Person() - " << this << endl;
	}
	void display() {
		cout << "display() - age is " << m_age << endl;
	}
};

Person test2() {
	return 40;
}

int main() {

	test2();

	getchar();
	return 0;
}