std::optional<T>::value_or
Min standard notice:
Returns the contained value if *this has a value, otherwise returns default_value.
# Declarations
template< class U >
constexpr T value_or( U&& default_value ) const&;
(since C++17)
template< class U >
constexpr T value_or( U&& default_value ) &&;
(since C++17)
# Parameters
default_value: the value to use in case *this is empty
# Return value
The current value if *this has a value, or default_value otherwise.
# Example
#include <cstdlib>
#include <iostream>
#include <optional>
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("SHELL").value_or("(none)") << '\n';
std::cout << maybe_getenv("MYPWD").value_or("(none)") << '\n';
}