Show every container element with for_each function - c++

Question

I like to understand more about templates. I tried to write my own function, that shows every container element.
void show_element(int i){
std::cout << i << endl;
}
int main(){
int dataarr[5]={1,4,66,88,9};
vector<int> data(&daten[0],&daten[0]+5);
std::for_each(data.begin(),data.end(),show_element)
...
My show_element function isn't generic yet. How do i have to write it, so that i can use it for different container-types?
template <typename T>
using type = typename T::value_type;
void show_element(type i){ //type i must be sthg like *data.begin()
std::cout << i << endl;
}
thanks a lot

Answer 1

Change to:
template <typename T>
void show_element(T const &i) { std::cout << i << std::endl; }
for_each applies the given function (e.g., show_element) on the result of dereferencing every iterator in the range [first, last), in order. So you don't need to take the value_type of the container.
Also in c++14 and above you could define a generic lambda:
auto show_element = [](auto const &i) { std::cout << i << std::endl; };
and use it as:
int arr[] = {1, 4, 66, 88, 9};
std::vector<int> data(arr, arr + sizeof(arr) / sizeof(int));
std::for_each(arr, arr + sizeof(arr) / sizeof(int), show_element);
LIVE DEMO

Answer 2

Instead of a function it is more flexible to use a class. In this case you can pass additional arguments to the functional object.
For example you could specify a stream where you are going to output the elements or a separator that will separate the elements in the stream.
The class can look the following way
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
template <typename T>
class show_elements
{
public:
show_elements( const std::string &separator = " ", std::ostream &os = std::cout )
: separator( separator ), os( os ) {}
std::ostream & operator ()( const T &value ) const
{
return os << value << separator;
}
protected:
std::string separator;
std::ostream &os;
};
int main()
{
int arr[] = { 1, 4, 66, 88, 9 };
std::vector<int> v( arr, arr + sizeof( arr ) / sizeof( *arr ) );
std::for_each( v.begin(), v.end(), show_elements<int>() );
std::cout << std::endl;
}
The program output is
1 4 66 88 9

Answer 3

Another simple way is to use range-based for loop.
for(auto& element : container) {
cout<<element<<endl;
}