【c++】cout過載能不能寫成成員函式，若能，寫出函式原型，若不能，說明原因

// cout過載能不能寫成成員函式，若能，寫出函式原型，若不能，說明原因

#include <iostream>
using namespace std;

// cout做友元
class A;
ostream& operator<<(ostream &out, const A &a);

class A
{
	friend ostream& operator<<(ostream &out, const A &a);
public:
	A(int n = 0):m(n)
	{}
private:
	int m;
};

ostream& operator<<(ostream &out, const A &a)
{
	out << a.m;
	return out;
}

int main()
{
	A a;
	cout << a << endl;
	return 0;
}




// cout並不是不可以做成員函式，但是它的輸出形式並不符合大家的習慣，所以還是不要把它寫到成員函式裡比較好
#include <iostream>
using namespace std;

class A
{
public:
	A(int n = 0) :m(n)
	{}
	// cout做成員函式
	ostream& operator<<(ostream &out)
	{
		out << m;
		return out;
	}
private:
	int m;
};

int main()
{
	A a;
	//注意輸出格式
	a << cout << endl;
	return 0;
}

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