How do I use for_each to output to cout? - c++

Question

Is there a more straight-forward way to do this?
for_each(v_Numbers.begin(), v_Numbers.end(), bind1st(operator<<, cout));
Without an explicit for loop, if possible.
EDIT:
How to do this for std::cin with a std::vector if possible? (How to read n elements only)?

Answer 1

You could achieve this using std::copy into a std::ostream_iterator:
std::vector<int> v_Numbers; // suppose this is the type
// put numbers in
std::copy(v_Numbers.begin(), v_Numbers.end(),
std::ostream_iterator<int>(std::cout));
It would be even nicer if you add some suffix:
std::copy(v_Numbers.begin(), v_Numbers.end(),
std::ostream_iterator<int>(std::cout, "\n"));
This assumes that your container is a vector<int>, so you will have to replace that part with the appropriate type.
Edit regarding reading input:
Conversely, you can copy from a range of std::istream_iterator into a vector using std::back_inserter:
std::vector<int> v_Numbers;
std::copy(std::istream_iterator<int>(std::cin), std::istream_iterator<int>(),
std::back_inserter(v_Numbers));
If you want to read n elements only, look at this question.

Answer 2

Another option — Boost.Lambda.
for_each(v.begin(), v.end(), cout << boost::lambda::_1);

Answer 3

Yep, but you must use std::copy algorithm:
#include <iostream>
#include <iterator>
#include <vector>
int main()
{
std::vector<int> a;
// fill a...
std::copy(a.begin(), a.end(), std::ostream_iterator<int>(std::cout));
}

Answer 4

yup, using lambda expression (C++ 11) we can inline printing of each element of a STL container to cout.
#include <iostream> // cout
#include <vector> // vector
#include <algorithm> // for_each
#include <iterator> // istream_iterator
using namespace std;
int main()
{
std::vector<int> v(10,2);
std::for_each(v.begin(), v.end(), [](int i)->void {std::cout << i <<endl;});
return 0;
}
For reading "n" values from cin to vector,
int main()
{
std::vector<int> v;
int elementsToRead;
cin>>elementsToRead; // Number of elements to copy
// Reading from istream
std::istream_iterator<int> ii2(std::cin);
std::copy_n(ii2, elementsToRead, std::back_inserter(v));
// printing updated vector
std::for_each(v.begin(), v.end(), [](int i)->void {cout << i <<endl;});
return 0;
}
(or) by using Lambda expression
std::for_each(std::istream_iterator<int>(cin),std::istream_iterator<int>(),[&v](int i)->void { v.push_back(i);});
To know more about Lambda expression # What is a lambda expression in C++11?

Answer 5

Not always appropriate in corporate code, but for the sake of enumerating options - if you really find other for_each / std::copy etc. solutions too verbose, you could write:
std::ostream& operator(std::ostream& os, const std::vector<My_Type>& v)
{
// pick one of the other implementations for here...
std::copy(std::istream_iterator<My_Type>(os), std::istream_iterator<My_Type>(),
std::back_inserter(v_Numbers));
}
It's much nicer if you're well-mannered (;-p) enough to only overload your specific instantiation of vector (which requires My_Type be more than a typedef to say int, though it's not hard to create a templated class to create new types wrapping an arbitrary type). Otherwise, if someone else does the same elsewhere in your translation unit, the streaming could become ambiguous.

Answer 6

I know the copy with the iterator is the optimal solution, but just to answer with for_each.
You could do:
#include <vector>
#include <algorithm>
#include <locale>
int main() {
using namespace std;
locale::global(locale(""));
wcout::imbue(locale());
vector<int> vec{1000,2000,3000,4000,5000};
for_each(vec.begin(), vec.end(), [](auto &x){wcout << x << endl;});
return 0;
}
But, for me, it's REALLY much more readable the simple for ...
#include <vector>
#include <locale>
int main() {
using namespace std;
locale::global(locale(""));
wcout::imbue(locale());
vector<int> vec{1000,2000,3000,4000,5000};
for(auto &v: vec) {
wcout << v << endl;
}
return 0;
}