C++ Template Question

[alantheweasel]

I have tried the following code , it doesnt work

#include <iostream>
#include <string>

using namespace std;

template <typename T>
T add (T & a, T & b);

template <typename T>
T add (T & a, T & b)
{
	return a + b;
}

int main()
{
	int i = 10;
	double d = 20.5;
	
	cout << add<double>(i, d) << "\n";
	
	return 0;
}

But i changed the following code ..

#include <iostream>
#include <string>

using namespace std;

template <typename T>
T add (T a, T b);

template <typename T>
T add (T a, T b)
{
	return a + b;
}

int main()
{
	int i = 10;
	double d = 20.5;
	
	cout << add<double>(i, d) << "\n";
	
	return 0;
}

then output ..

30.5

I dont know why it failed by using reference value

[o1vk4iN6]

You'd be creating a temporary value (implicit conversion from int to double) to be able to pass by reference. Perhaps RValue would be a better term here, they shouldn't be modified so they need to be passed as const.

template <typename T>
T add (const T& a, const T& b)
{
	return a + b;
}


int main()
{
	int i = 10;
	double d = 20.5;
	
	cout << add<double>(i, d) << "\n";
	
	return 0;
}