std::get_if(std::variant)

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Utilities library

Language support

Type support (basic types, RTTI)

Library feature-test macros(C++20)

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Variadic functions

initializer_list

(C++11)

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(C++20)

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(C++26)

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(C++20)

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Contract support(C++26)

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three_way_comparablethree_way_comparable_with

(C++20)(C++20)

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(C++20)

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(C++20)

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(C++20)

common_comparison_category

(C++20)

compare_three_way_result

(C++20)

(C++20)

(C++20)

(C++20)

(C++20)

compare_strong_order_fallback

(C++20)

compare_weak_order_fallback

(C++20)

compare_partial_order_fallback

(C++20)

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(C++20)(C++20)(C++20)

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cmp_equalcmp_lesscmp_less_than

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cmp_not_equalcmp_greatercmp_greater_than

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in_range

(C++20)

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Common vocabulary types

pair
tuple (C++11)
optional (C++17)
any (C++17)
variant (C++17)

tuple_size (C++11)
tuple_element (C++11)
apply (C++17)
make_from_tuple (C++17)
expected (C++23)

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std::variant

Member functions
variant::variant
variant::~variant
variant::operator=
Observers
variant::index
variant::valueless_by_exception
Modifiers
variant::emplace
variant::swap
Visitation
variant::visit (C++26)
Non-member functions
visit(std::variant)
holds_alternative
get(std::variant)
get_if
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)
swap(std::variant)
Helper classes
monostate
bad_variant_access
variant_size
variant_alternative
hash<std::variant>
Helper objects
variant_npos

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

1) Index-based non-throwing accessor: Ifpv is not a null pointer andpv->index()== I, returns a pointer to the value stored in the variant pointed to bypv. Otherwise, returns a null pointer value. The call is ill-formed ifI is not a valid index in the variant.

2) Type-based non-throwing accessor: Equivalent to(1) withI being the zero-based index ofT inTypes.... The call is ill-formed ifT is not a unique element ofTypes....

[edit]Template parameters

I	-	index to look up
Type	-	unique type to look up

[edit]Parameters

pointer to a variant

[edit]Return value

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

[edit]Example

Run this code

#include <iostream>#include <variant> int main(){auto check_value=[](conststd::variant<int,float>& v){if(constint* pval= std::get_if<int>(&v))std::cout<<"variant value: "<<*pval<<'\n';elsestd::cout<<"failed to get value!"<<'\n';}; std::variant<int,float> v{12}, w{3.f};    check_value(v);    check_value(w);}