std::optional was introduced in C++17 to provide a safer, more expressive way of handling values that may or may not be present. While raw pointers (including nullptr) have long been a de facto idiom for nullable returns, std::optional offers several advantages that align with modern C++ best practices:
| Feature | Raw Pointer | std::optional |
|---|---|---|
| Type safety | The compiler cannot distinguish between a valid object and a null pointer without manual checks. | The presence of a value is encoded in the type (`std::optional |
| `), forcing explicit handling. | ||
| Value semantics | Returning a pointer can accidentally lead to shared ownership or unintended lifetime extension. | The wrapped value is stored directly (or via a small buffer), guaranteeing copy/move semantics. |
| Memory overhead | Pointers consume 8 bytes on 64‑bit systems and require a separate allocation if dynamic. | Only an extra flag (bool or bitfield) is needed in addition to the value; no dynamic allocation. |
| RAII compliance | Raw pointers need manual delete/free or smart‑pointer helpers. |
The optional owns its value; destruction is automatic. |
| Error handling | Must rely on sentinel values or exception handling. | Provides has_value(), value_or(), and operator*()/operator-> for natural access. |
Practical Example
#include <optional>
#include <string>
#include <iostream>
std::optional<std::string> read_file(const std::string& path) {
if (path == "missing.txt")
return std::nullopt; // No value
return std::string("File content..."); // Value present
}
int main() {
auto content = read_file("missing.txt");
if (!content) {
std::cerr << "File not found.\n";
return 1;
}
// Access the string safely
std::cout << *content << '\n';
}With raw pointers:
std::string* read_file(const std::string& path) {
if (path == "missing.txt")
return nullptr;
return new std::string("File content...");
}
int main() {
std::unique_ptr<std::string> content(read_file("missing.txt"));
if (!content) {
std::cerr << "File not found.\n";
return 1;
}
std::cout << *content << '\n';
}The pointer version requires manual memory management and uses unique_ptr to avoid leaks—an extra layer of complexity that std::optional removes.
When to Still Use Pointers
- Polymorphic objects: If the return type is a base class pointer to a derived object, `std::unique_ptr
- Legacy interfaces: When interfacing with APIs that already use pointers,
std::optionalmay not be applicable without refactoring.
Bottom Line
std::optional is a first‑class citizen in C++17 and later, and for most functions that return a value that might be absent, it should be the default choice. It makes intent explicit, enforces safer code, and keeps the implementation free from manual memory management pitfalls.