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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