"error: cannot convert ‘Funct’ to ‘int’ in initialization" when trying to use functors.

[waqqassheikh]

I'm trying to get the hang of functors but I get this error on line 18.
I'd really appreciate it if someone could tell me where I've gone wrong.

#include <vector>
#include <iostream>
#include <algorithm>

class Funct
{
		int Total;
	public:
		Funct() : Total(0) {};
		void operator() (int& i )
		{
			Total += i;
		}
} funct;

int main()
{
	std::vector<int> v = {1,5};
	int sum = std::for_each(v.begin(),v.end(),funct); //Error here
	std::cout<<"The total is "<<sum<<".\n";
}

[vlad from moscow]

You shall use funct()
Oops, I am sorry. I did not see that you already defined the object.
The problem is that your operator function does not return anything. And you are trying assign a pointer to fucntion to int. You can redefine your class the following way

class Funct
{
		int Total;
	public:
		Funct() : Total(0) {};
		void operator() (int& i )
		{
			Total += i;
		}
		int get_total() const
		{
			return ( Total );
		}

} funct;

And then call

std::for_each(v.begin(),v.end(),funct); 
int sum = func.get_total();

Or

int sum = std::for_each(v.begin(),v.end(),funct).get_total();

[waqqassheikh]

I used funct() but then it said that the function expects one argument and no arguments have been provided.

[vlad from moscow]

I have updated my message.

[waqqassheikh]

Thanks, that worked but I get incorrect result.
Instead of showing a total of 6, it shows a total of 0.

[vlad from moscow]

It is my mistake. Shall be

int sum = std::for_each(v.begin(),v.end(),funct).get_total();

I made the mistake because I thought that Total was defined as static member.

[waqqassheikh]

Thanks, that worked but i'm confused.
According to the documentation, std::for_each has the same return type as the functor.
our function returned void, so how did we call the get_total() method on it?

[waqqassheikh]

Would this code be considered acceptable?

#include <vector>
#include <iostream>
#include <algorithm>

class Funct
{
		int mTotal;
	public:
		Funct() : mTotal(0) {};

		int operator() (int& i )
		{
			return (mTotal += i);
		}
	

} funct;

int main()
{
	std::vector<int> v = {1,5};
	int sum = std::for_each(v.begin(),v.end(),funct);
	std::cout<<"Sum: "<<sum<<".\n";
}

[vlad from moscow]

According to the documentation, std::for_each has the same return type as the functor.
our function returned void, so how did we call the get_total() method on it?

The algorithm returns what was passed to it. As you are passing the object it is returned. If you would pass a pointer to function it were returned.

Your last code shall not be compiled because the object is returned.
You could change your class the following way adding the conversion operator

class Funct
{
		int mTotal;
	public:
		Funct() : mTotal(0) {};

		int operator() (int& i )
		{
			return (mTotal += i);
		}
	
		operator int() const
		{
			return ( mTotali);
		}

} funct;

In this case it shall work.

[ne555]

int sum = std::accumulate(v.begin(), v.end(), 0);

[waqqassheikh]

@vlad from moscow. That's brilliant. Thansk a lot for your help :-)