类模板友元函数坑死人不偿命的错误

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错误例程：

#include<iostream>

using namespace std;

template<class T>
class Student
{
private:
	T age;
public:
	Student(T age_) :age(age_){}
	friend bool operator==(const Student<T>& s1, const Student<T>& s2);
};

int main()
{
	Student<int> s1(1);
	Student<int> s2(2);
	if (s1 == s2)
		cout << "相等" << endl;
	else
		cout << "不相等" << endl;

	cin.get();
	return 0;
}

template<class T>
bool operator==(const Student<T>& s1, const Student<T>& s2)
{
	if (s2.age == s1.age)
	{
		return true;
	}
	return false;
}

正确例程：

#include<iostream>

using namespace std;

template<class T>
class Student
{
private:
	T age;
public:
	Student(T age_) :age(age_){}

	template<class T>
	friend bool operator==(const Student<T>& s1, const Student<T>& s2);
};

int main()
{
	Student<int> s1(1);
	Student<int> s2(2);
	if (s1 == s2)
		cout << "相等" << endl;
	else
		cout << "不相等" << endl;

	cin.get();
	return 0;
}

template<class T>
bool operator==(const Student<T>& s1, const Student<T>& s2)
{
	if (s2.age == s1.age)
	{
		return true;
	}
	return false;
}

类模板友元函数坑死人不偿命的错误

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原文地址：http://blog.csdn.net/linukey/article/details/46367725