Search⌘ K
AI Features
Home
Courses
C++17 in Detail: A Deep Dive

std::optional Creation

Explore multiple ways to create std optional in C++17, including initializing as empty, directly with a value, using deduction guides, make optional, and in_place. Understand how these methods simplify handling nullable and complex types effectively.

We'll cover the following...

There are several ways to create std::optional:

  • Initialise as empty
  • Directly with a value
  • With a value using deduction guides
  • By using make_optional
  • With std::in_place
  • From other optional

See code below:

C++ 17
#include <iostream>
#include <optional>
#include <complex>
#include <vector>
using namespace std;
int main() {
  // empty:
  std::optional<int> oEmpty;
  std::optional<float> oFloat = std::nullopt;
  cout << "oEmpty = " << *oEmpty << endl;
  cout << "oFloat = " << *oFloat << endl;
  // direct:
  std::optional<int> oInt(10);
  std::optional oIntDeduced(10); // deduction guides
  cout << "oInt = " << *oInt << endl;
  cout << "oIntDeduced = " << *oIntDeduced << endl;
  // make_optional
  auto oDouble = std::make_optional(3.0);
  auto oComplex = std::make_optional<std::complex<double>>(3.0, 4.0);
  cout << "oDouble = " << *oDouble << endl;
  cout << "oComplex = " << *oComplex << endl;
  // in_place
  std::optional<std::complex<double>> o7{std::in_place, 3.0, 4.0};
  cout << "o7 = " << *o7 << endl;
  // will call vector with direct init of {1, 2, 3}
  std::optional<std::vector<int>> oVec(std::in_place, {1, 2, 3});
  
  // copy from other optional:
  auto oIntCopy = oInt;
  cout << "oIntCopy = " << *oIntCopy << endl;
}

As you can see in the above code sample, you have a lot of flexibility with the creation of optional. It’s straightforward for primitive types, and this simplicity is extended even to complex types.

And, if you want the full control over the creation and efficiency, it’s also good to know in_place helper types. We’ll tackle that next.