std::optional (C++17)

In a Nutshell

A container used to represent "a value that may not exist," which is safer and more intuitive than returning a status code plus a pointer or using output parameters.

Header File

<optional>

Core API Cheat Sheet

Operation	Signature	Description
Construct	`optional()`	Default constructor, does not contain a value
Assign empty	`reset()` or `= nullopt`	Sets the state to valueless
Check has value	`has_value()`	Returns `true` if a value is present
Check has value	`operator bool()`	Same as above
Get value	`operator*()` or `operator->()`	Dereference to get value (undefined behavior if no value)
Safe get	`value()`	Get value, throws `bad_optional_access` if no value
Value or default	`value_or()`	Returns value if present, otherwise returns default value
In-place construct	`emplace()`	Constructs value in-place
Reset	`reset()`	Destroys the contained value

Minimal Example

Expand (25 lines)Collapse

cpp

#include <optional>
#include <iostream>

// A function that might fail
std::optional<int> divide(int a, int b) {
    if (b == 0) {
        return std::nullopt; // Indicate failure
    }
    return a / b; // Indicate success
}

int main() {
    auto result = divide(10, 2);

    // Check if result contains a value
    if (result) {
        std::cout << "Result: " << *result << '\n';
    } else {
        std::cout << "Division failed\n";
    }

    // Get value or default
    auto safe_result = divide(10, 0).value_or(-1);
    std::cout << "Safe result: " << safe_result << '\n';
}

Embedded Applicability: High

Zero-overhead abstraction; when no value is present, it only occupies storage space equivalent to one byte (plus alignment/padding), and involves no heap allocation.
Can replace raw pointers as return values for functions that may fail, avoiding the risks of null pointer dereferencing.
Fully supported since C++17; member functions are comprehensively constexpr in C++23 and later, further broadening the range of applicable scenarios.

Compiler Support

GCC	Clang	MSVC
TBD	TBD	TBD

std::optional (C++17) ​

In a Nutshell ​

Header File ​

Core API Cheat Sheet ​

Minimal Example ​

Embedded Applicability: High ​

Compiler Support ​

See Also ​