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std::variant::index

From cppreference.com
< cpp‎ | utility‎ | variant
 
 
 
 
constexpr std::size_t index() const
(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] Exceptions

noexcept specification:  
noexcept
  

[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 given type appears exactly once in a variant
(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]