std::optional<T>::operator->, std::optional<T>::operator*
constexpr const T* operator->() const noexcept; | (1) | (since C++17) |
constexpr T* operator->() noexcept; | (2) | (since C++17) |
constexpr const T& operator*() const& noexcept; | (3) | (since C++17) |
constexpr T& operator*() & noexcept; | (4) | (since C++17) |
constexpr const T&& operator*() const&& noexcept; | (5) | (since C++17) |
constexpr T&& operator*() && noexcept; | (6) | (since C++17) |
Accesses the contained value.
1,2) Returns a pointer to the contained value.
3-6) Returns a reference to the contained value.
| If | (until C++26) |
| If
| (since C++26) |
Return value
Pointer or reference to the contained value.
Notes
Check has_value() or operator bool() before calling these functions. Alternatively, value() or value_or() may be used.
Example
#include <iomanip>
#include <iostream>
#include <optional>
#include <string>
int main()
{
using namespace std::string_literals;
std::optional<int> opt1{1};
std::cout << "opt1: " << *opt1 << '\n';
*opt1 = 2;
std::cout << "opt1: " << *opt1 << '\n';
std::optional<std::string> opt2{"abc"s};
std::cout << "opt2: " << std::quoted(*opt2) << ", size: " << opt2->size() << '\n';
// You can "take" the contained value by calling operator* on an rvalue to optional
auto taken = *std::move(opt2);
std::cout << "taken: " << std::quoted(taken) << "\n"
"opt2: " << std::quoted(*opt2) << ", size: " << opt2->size() << '\n';
}
Output:
opt1: 1 opt1: 2 opt2: "abc", size: 3 taken: "abc" opt2: "", size: 0
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2762 | C++17 |
operator-> and operator* might be potentially-throwing | made noexcept |
See also
| returns the contained value (public member function) |
|
| returns the contained value if available, another value otherwise (public member function) |
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