constexpr std::size_t index() const noexcept; | (since C++17) |
Returns the zero-based index of the alternative that is currently held by the variant.
If the variant is valueless_by_exception, returns variant_npos.
#include <variant>
#include <string>
#include <iostream>
int main()
{
std::variant<int, std::string> v = "abc";
std::cout << "v.index = " << v.index() << '\n';
v = {};
std::cout << "v.index = " << v.index() << '\n';
}Output:
v.index = 1 v.index = 0
|
(C++17) | checks if a variant currently holds a given type (function template) |
|
(C++17) | reads the value of the variant given the index or the type (if the type is unique), throws on error (function template) |
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https://en.cppreference.com/w/cpp/utility/variant/index