std::get_if

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Library feature-test macros
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
integer_sequence (C++14)
Relational operators (deprecated)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Elementary string conversions
to_chars (C++17)
from_chars (C++17)
chars_format (C++17)
Type operations
declval (C++11)
as_const (C++17)

std::variant

Member functions

variant::variant

variant::~variant

variant::operator=

Observers

variant::index

variant::valueless_by_exception

Modifiers

variant::emplace

variant::swap

Non-member functions

visit

holds_alternative

get

get_if

operator==operator!=operator<operator<=operator>operator>=

swap

Helper classes

monostate

bad_variant_access

variant_size

variant_alternative

hash

Helper objects

variant_npos

Defined in header <variant>
	(1)	(since C++17)
template <std::size_t I, class... Types> constexpr std::add_pointer_t< std::variant_alternative_t<I, std::variant<Types...>> > get_if(std::variant<Types...>* pv) noexcept;
template <std::size_t I, class... Types> constexpr std::add_pointer_t< const std::variant_alternative_t<I, variant<Types...>> > get_if(const std::variant<Types...>* pv) noexcept;
			(2)	(since C++17)
template <class T, class... Types> constexpr std::add_pointer_t<T> get_if(std::variant<Types...>* pv) noexcept;
template <class T, class... Types> constexpr std::add_pointer_t<const T> get_if(const std::variant<Types...>* pv) noexcept;

1) Index-based non-throwing accessor: If pv is not a null pointer and pv->index() == I, returns a pointer to the value stored in the variant pointed to by pv. Otherwise, returns a null pointer value. The call is ill-formed if I is not a valid index in the variant.

2) Type-based non-throwing accessor: Equivalent to (1) with I being the zero-based index of T in Types.... The call is ill-formed if T is not a unique element of Types....

Parameters

I	-	index to look up
Type	-	unique type to look up
pv	-	pointer to a variant

Return value

Pointer to the value stored in the pointed-to variant or null pointer on error.

Example

Run this code

#include <variant>
#include <iostream>

int main()
{
    std::variant<int, float> v{12};

    if(auto pval = std::get_if<int>(&v))
      std::cout << "variant value: " << *pval << '\n'; 
    else 
      std::cout << "failed to get value!" << '\n'; 
}

Output:

variant value: 12

See also

std::get(std::variant) (C++17)

reads the value of the variant given the index or the type (if the type is unique), throws on error (function template)