Is it possible to print vector content with width of 5? - c++

Question

Here is what I have to do!
Write a program to perform the following steps.
Allocate memory dynamically to store an array of 10 ints.
Assign each int a random value between 1 and 100.
Copy each of the 10 random ints to a vector of ints.
Print the dynamically allocated array of ints and the vector of ints, each with a width of 5, as shown in the sample output below.
I have trouble with the last point. My code is working perfectly, but I don't know how to set width in vector of ints so it is the same as array of ints.
#include<iostream>
#include<iomanip>
#include<cstdlib>
#include <vector>
#include <algorithm>
#include <iterator>
#include <stdexcept>
using namespace std;
int main(){
const int SIZE = 10;
int *arr = new int[SIZE];
//assign rand numbers between 0 and 100
for (int i = 0; i < SIZE; ++i){
*(arr + i) = rand() % 100+1;
}
//print array
for (int i = 0; i < SIZE; ++i){
cout << setw(5) << *(arr +i) << " ";
}
std::vector<int> integers (arr, arr + 10);
std::ostream_iterator<int> output(cout, " ");
cout << endl;
cout << "Vector integers contain: " << endl;
std::copy(integers.begin(), integers.end(), output);
return 0;
}

Answer 1

Your code works fine as is. cout << setw(5); sets the width just fine. You could also use cout.width(5);.

Answer 2

If you really want to do this with an ostream_iterator, the cleanest way is probably with a small proxy class:
class integer {
int i;
public:
integer(int i) : i(i) {}
friend std::ostream &operator<<(std::ostream &os, integer i) {
return os << std::setw(5) < i.i;
}
};
Then to write them out, use that type as the template parameter to the ostream_iterator:
std::copy(integers.begin(), integers.end(),
std::ostream_iterator<integer>(std::cout, ' '));
This will create a temporary integer object, then write it out using the operator<< for integer, which sets the width. At least in theory, this probably imposes some overhead, but I'd expect (at least with optimization enabled) most compilers will probably see through the subterfuge (so to speak) and eliminate any extra copies and such.
Of course, if the width isn't cast in concrete, you could make integer a template, and supply the width as a template parameter:
template <int N>
class integer {
// ...
return os << std::setw(N) < i.i;
Unless I really needed to use an ostream_iterator, I think I'd use a range-based for loop though:
for (int i : integers)
std::cout << std::setw(5) << i << ' ';

Answer 3

Since the width of a stream is reset to 0 everytime it is used, you can't use a std::ostream_iterator<int> (well, you could by using a custom std::num_get<char> facet which restores the width but that seems a bit radical).
You can print the std::vector<int> like this, however:
std::for_each(integers.begin(), integers.end(),
[](int v){ std::cout << std::setw(5) << v << ' '; });