How I can fill a unique_ptr that is pointing to a char array?

Question

It's possible to put something in to an unique_ptr that is pointing to a char array, something like this:

#include <iostream>
#include <memory>
#define LEN 100
using std::cout, std::cin;

int main() {
    std::unique_ptr<char[]> ptr {new char[LEN]};

    cout << "Enter a word: \n";
    cin >> ptr;
}

I tried with this and also with getline but doesn't work

Yes, I can use it but is a exercise where you must use unique_ptr — Giovanni Scordilli, Aug 17 '23 at 15:59
Do you know that a `unique_ptr` stores a pointer to the array and that you can access the pointer with `.get()`? — j6t, Aug 17 '23 at 16:01
@AlanBirtles Yes, the second one. The first one, not so much. It's even removed in C++20. — Ted Lyngmo, Aug 17 '23 at 16:04
the exercise only makes sense when they told you how to use the stuff. When in doubt you can always refer to documentation: https://en.cppreference.com/w/cpp/memory/unique_ptr — 463035818_is_not_an_ai, Aug 17 '23 at 16:05
@GiovanniScordilli Just don't do `std::cin >> ptr.get();` - It's unsafe and removed from the standard library since C++20. Use Alan's second suggestion: `cin.getline(ptr.get(), LEN);` — Ted Lyngmo, Aug 17 '23 at 16:05
If it's unsafe by C++ standards, it's **superfund** unsafe! Monkey with a gun. — Eljay, Aug 17 '23 at 16:07
@TedLyngmo I wouldn't personally use either and just use `std::string` instead — Alan Birtles, Aug 17 '23 at 16:21
@AlanBirtles Of course but OP mentioned in a comment that `unique_ptr` must be used. — Ted Lyngmo, Aug 17 '23 at 16:24
@GiovanniScordilli does it have to be `char[]`, though? Why not `std::unique_ptr` at least? Standard practice is to avoid `new` whenever possible. If you must use `char[]`, at least consider using `std::make_unique(LEN)` — Remy Lebeau, Aug 17 '23 at 16:39
If you don't think it is a std::string, consider std::vector or possibly std::vector if you are interested in binary data instead of a stirng of characters. The guideline @RemyLebeau is talking about is this one [C++ core coding guidelines R.11](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#r11-avoid-calling-new-and-delete-explicitly) — Pepijn Kramer, Aug 17 '23 at 17:52

score 0 · Accepted Answer · answered Aug 17 '23 at 16:55

It depends on what kind of an array you want. For dynamically sized data, simply use a std::string. For something statically sized, a3 below wins in terms of efficiency, a simple buffer on the stack. It doesn’t use a unique_ptr, but it’s unclear why the exercise forces you to use dynamic allocation for no good reason.

#include <array>
#include <cstdint>
#include <iostream>
#include <memory>

namespace {
constexpr size_t LEN{100};
}

int main() {
  std::unique_ptr a1{std::make_unique<char[]>(LEN)};
  std::unique_ptr a2{std::make_unique<std::array<char, LEN>>()};
  std::array<char, LEN> a3;

  std::cout << "Enter a word: \n";
  std::cin.getline(a1.get(), LEN);
  std::cout << "Enter a word: \n";
  std::cin.getline(a2->data(), LEN);
  std::cout << "Enter a word: \n";
  std::cin.getline(a3.data(), LEN);

  std::cout << a1.get() << '\n' << a2->data() << '\n' << a3.data() << '\n';
}

How I can fill a unique_ptr that is pointing to a char array?

1 Answers1