# std::conditional

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< cpp‎ | types

Defined in header `<type_traits>` |  |
template< bool B, class T, class F > struct conditional; |  | (since C++11)

Provides member typedef `type`, which is defined as `T` if `B` is true at compile time, or as `F` if `B` is false.

### Member types

Member type | Definition
`type` | `T` if B == true, `F` if B == false

### Helper types

template< bool B, class T, class F > using conditional_t = typename conditional<B,T,F>::type; |  | (since C++14)

### Possible implementation

    template<bool B, class T, class F>
    struct conditional { typedef T type; };

    template<class T, class F>
    struct conditional<false, T, F> { typedef F type; };

### Example

Run this code

    #include <iostream>
    #include <type_traits>
    #include <typeinfo>

    int main()
    {
        typedef std::conditional<true, int, double>::type Type1;
        typedef std::conditional<false, int, double>::type Type2;
        typedef std::conditional<sizeof(int) >= sizeof(double), int, double>::type Type3;

        std::cout << typeid(Type1).name() << '\n';
        std::cout << typeid(Type2).name() << '\n';
        std::cout << typeid(Type3).name() << '\n';
    }

Output:

    i
    d
    d

### See also

enable_if (C++11) | hides a function overload or template specialization based on compile-time boolean (class template)

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