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std::experi...al::value_or(3) C++ Standard Libarystd::experi...al::value_or(3) NAME std::experimental::optional::value_or - std::experimental::op- tional::value_or Synopsis template< class U > (library funda- mentals TS) constexpr T value_or( U&& default_value ) const&; template< class U > (library funda- mentals TS) constexpr T value_or( U&& default_value ) &&; 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)) Parameters default_value - the value to use in case *this is empty Type requirements - T must meet the requirements of CopyConstructible in order to use overload (1). - T must meet the requirements of MoveConstructible in order to use overload (2). - U&& must be convertible to T Return value The current value if *this has a value, or default_value otherwise. Exceptions Any exception thrown by the selected constructor of the return value T. Example // Run this code #include <experimental/optional> #include <iostream> #include <cstdlib> std::experimental::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) See also value returns the contained value (public member function) http://cppreference.com 2022.07.31 std::experi...al::value_or(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Exceptions | Example | Possible output: | See also
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