std::optional (C++17)

One-Liner

A container that represents "a value may not exist," which is safer and more intuitive than returning a raw pointer or using an output parameter.

Header

#include <optional>

Core API Quick Reference

Operation	Signature	Description
Construct	optional()	Default construct, contains no value
Assign empty	optional& operator=(nullopt_t)	Sets the state to no value
Check for value	explicit operator bool() const	Returns true when a value is present
Check for value	bool has_value() const	Same as above
Get value	T& operator*()	Dereferences to get the value (undefined behavior if no value is present)
Safe get	T& value()	Gets the value, throws bad_optional_access if no value is present
Get or default	T value_or(const T& default_value) const	Returns the value if present, otherwise returns the default value
In-place construct	T& emplace(Args&&... args)	Constructs the value in-place
Reset	void reset() noexcept	Destroys the contained value

Minimal Example

#include <iostream>
#include <optional>
#include <string>

std::optional<std::string> find(bool b) {
    return b ? std::optional<std::string>{"found"} : std::nullopt;
}

int main() {
    auto res = find(false);
    std::cout << res.value_or("not found") << '\n';

    if (auto val = find(true))
        std::cout << *val << '\n';
}

Embedded Applicability: High

• A zero-overhead abstraction; when no value is present, it only occupies storage the size of one bool, with no heap allocation involved
• Can replace raw pointers as function return values for operations that might fail, avoiding the risk of null pointer dereferences
• Fully supported since C++17, and member functions are comprehensively constexpr starting in C++23, further broadening its use cases

Compiler Support

GCC	Clang	MSVC
TBA	TBA	TBA

See Also

• cppreference: std::optional

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