Namespaces
Variants
Views
Actions

std::variant<Types...>::index

From cppreference.com
< cpp‎ | utility‎ | variant
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++17)

Elementary string conversions
(C++17)
(C++17)
 
 
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.

[edit] Example

#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

[edit] See also

checks if a variant currently holds a given type
(function template) [edit]
reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template) [edit]