C++: What is std::optional and when to use it?

std::optional — value that may or may not exist.

1#include <optional>
2
3std::optional<int> divide(int a, int b) {
4    if (b == 0) return std::nullopt;
5    return a / b;
6}
7
8auto result = divide(10, 3);
9if (result) {
10    std::cout << *result;
11}

Benefits:

• Clearer than null pointers
• No heap allocation
• Self-documenting API
• No sentinel values

Operations:

• has_value(): check existence
• value(): get with exception
• value_or(default): get with fallback
• *opt: dereference (UB if empty)

Use when:

• Function may not return a value
• Optional member variables
• Replace null pointer patterns