std::get_if

 

C++

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Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

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initializer_list (C++11)

bitset

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rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

optional, any and variant (C++17)

optional

any

variant

in_placein_place_tin_place_type_tin_place_index_t

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pair

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Swap, forward and move

swap

exchange (C++14)

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declval (C++11)

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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

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

uses_allocator

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)
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)
			(2)	(since C++17)
template <class T, class... Types> constexpr std::add_pointer_t<T> get_if(variant<Types...>* pv)
template <class T, class... Types> constexpr std::add_pointer_t<const T> get_if(const variant<Types...>* pv)

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 or if T_I is a (possibly cv-qualified) type void.

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... or if T_I is a (possibly cv-qualified) type void.

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.

Exceptions

1,2)

noexcept specification:  

noexcept

  

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)