std::optional::value_or
From cppreference.com
| template< class U >
constexpr T value_or( U&& default_value ) const&; |
(since C++17) | |
| template< class U >
T value_or( U&& default_value ) &&; |
(since C++17) | |
Returns the contained value if *this has a value, otherwise returns default_value.
1) Equivalent to bool(*this) ? **this : static_cast<T>(std::forward<U>(default_value))
2) Equivalent to bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(default_value))
Contents |
[edit] Parameters
| default_value | - | the value to use in case *this is empty
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| Type requirements | ||
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T must meet the requirements of CopyConstructible in order to use overload (1).
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T must meet the requirements of MoveConstructible in order to use overload (2).
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U&& must be convertible to T
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[edit] Return value
The current value if *this has a value, or default_value otherwise.
[edit] Exceptions
Any exception thrown by the selected constructor of the return value T.
[edit] Example
Run this code
#include <optional> #include <iostream> #include <cstdlib> std::optional<const char*> maybe_getenv(const char* n) { if(const char* x = std::getenv(n)) return x; else return {}; } int main() { std::cout << maybe_getenv("MYPWD").value_or("(none)") << '\n'; }
Possible output:
(none)
[edit] See also
| returns the contained value (public member function) |