std::function error conversion from ‘x' to non-scalar type ‘y’ requested?

November 18, 2022

I have the following code to demonstrate a function been called inside another function.

The below code works correctly:

#include <iostream>
#include <functional>

int thirds(int a) 
{
    return a + 1;
}

template <typename T, typename B , typename L>
//------------------------------------------------VVVVV-
int hello(T x, B y, L func) 
{
    int first = x + 1;
    int second = y + 1;
    int third = func(6);
    return first + second + third;
}

int add() 
{
    std::function<int(int)> myfunc = thirds;
    return hello(1, 1, myfunc);  // pass thirds function from here
}

int main() 
{
    std::cout << add();
    return 0;
}

Live Here

But Now I want to pass a function( thirds) of type Number ( A C++ class ) with return type std::vector<uint8_t>

thirds function

std::vector<uint8_t> thirds(Number &N) 
{  
    std::vector<uint8_t> z;
    z.push_back(N.z);
    return z ;
}

Here is the full code ( Live here )and How I am doing it.

#include <stdio.h>
#include <iostream>
#include <functional>

class Number{
    public:
      int z = 5;
};

std::vector<uint8_t> thirds(Number &N) 
{  
    std::vector<uint8_t> z;
    z.push_back(N.z);
    return z ;
}

template <typename T, typename B ,  typename L>
//------------------------------------------------VVVVV-
int hello(T x, B y, L func) 
{
    int first = x + 1;
    int second = y + 1;
    Number N;
    std::vector<uint8_t> third = func(N);
    return first + second ;
}

int add() 
{
    std::function<std::vector<uint8_t>(Number)> myfunc = &thirds;
    return hello(1, 1, myfunc);
}

int main() 
{
    std::cout << add();
    return 0;
}

I am getting a error:

 error: conversion from ‘std::vector (*)(Number&)’ to non-scalar type ‘std::function(Number)>’ requested
     std::function<std::vector<uint8_t>(Number)> myfunc = &thirds;

Can Someone please show me what I am doing wrong? How can I solve it?