# std::make_unique, std::make_unique_default_init

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< cpp‎ | memory‎ | unique ptr

Defined in header `<memory>` |  |
template< class T, class... Args > unique_ptr<T> make_unique( Args&&... args ); | (1) | (since C++14) (only for non-array types)
template< class T > unique_ptr<T> make_unique( std::size_t size ); | (2) | (since C++14) (only for array types with unknown bound)
template< class T, class... Args > /* unspecified */ make_unique( Args&&... args ) = delete; | (3) | (since C++14) (only for array types with known bound)
template< class T > unique_ptr<T> make_unique_default_init( ); | (4) | (since C++20) (only for non-array types)
template< class T > unique_ptr<T> make_unique_default_init( std::size_t size ); | (5) | (since C++20) (only for array types with unknown bound)
template< class T, class... Args > /* unspecified */ make_unique_default_init( Args&&... args ) = delete; | (6) | (since C++20) (only for array types with known bound)

Constructs an object of type `T` and wraps it in a std::unique_ptr.

1) Constructs a non-array type `T`. The arguments `args` are passed to the constructor of `T`. This overload only participates in overload resolution if `T` is not an array type. The function is equivalent to:

    unique_ptr<T>(new T(std::forward<Args>(args)...))

2) Constructs an array of unknown bound `T`. This overload only participates in overload resolution if `T` is an array of unknown bound. The function is equivalent to:

    unique_ptr<T>(new typename std::remove_extent<T>::type[size]())

3,6) Construction of arrays of known bound is disallowed.
4) Same as (1), except that the object is default-initialized. This overload only participates in overload resolution if `T` is not an array type. The function is equivalent to:

    unique_ptr<T>(new T)

5) Same as (2), except that the array is default-initialized. This overload only participates in overload resolution if `T` is an array of unknown bound. The function is equivalent to:

    unique_ptr<T>(new typename std::remove_extent<T>::type[size])

### Parameters

args | - | list of arguments with which an instance of `T` will be constructed.
size | - | the size of the array to construct

### Return value

std::unique_ptr of an instance of type `T`.

### Exceptions

May throw std::bad_alloc or any exception thrown by the constructor of `T`. If an exception is thrown, this function has no effect.

### Possible Implementation

    // note: this implementation does not disable this overload for array types
    template<typename T, typename... Args>
    std::unique_ptr<T> make_unique(Args&&... args)
    {
        return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
    }

### Notes

Unlike std::make_shared (which has std::allocate_shared), `std::make_unique` does not have an allocator-aware counterpart. A hypothetical `allocate_unique` would be required to invent the deleter type `D` for the `unique_ptr<T,D>` it returns which would contain an allocator object and invoke both `destroy` and `deallocate` in its `operator()`.

### Example

Run this code

    #include <iostream>
    #include <memory>

    struct Vec3
    {
        int x, y, z;
        Vec3() : x(0), y(0), z(0) { }
        Vec3(int x, int y, int z) :x(x), y(y), z(z) { }
        friend std::ostream& operator<<(std::ostream& os, Vec3& v) {
            return os << '{' << "x:" << v.x << " y:" << v.y << " z:" << v.z  << '}';
        }
    };

    int main()
    {
        // Use the default constructor.
        std::unique_ptr<Vec3> v1 = std::make_unique<Vec3>();
        // Use the constructor that matches these arguments
        std::unique_ptr<Vec3> v2 = std::make_unique<Vec3>(0, 1, 2);
        // Create a unique_ptr to an array of 5 elements
        std::unique_ptr<Vec3[]> v3 = std::make_unique<Vec3[]>(5);

        std::cout << "make_unique<Vec3>():      " << *v1 << '\n'
                  << "make_unique<Vec3>(0,1,2): " << *v2 << '\n'
                  << "make_unique<Vec3[]>(5):   " << '\n';
        for (int i = 0; i < 5; i++) {
            std::cout << "     " << v3[i] << '\n';
        }
    }

Output:

    make_unique<Vec3>():      {x:0 y:0 z:0}
    make_unique<Vec3>(0,1,2): {x:0 y:1 z:2}
    make_unique<Vec3[]>(5):
         {x:0 y:0 z:0}
         {x:0 y:0 z:0}
         {x:0 y:0 z:0}
         {x:0 y:0 z:0}
         {x:0 y:0 z:0}

### See also

(constructor) | constructs a new `unique_ptr` (public member function)
make_shared make_shared_default_init (C++20) | creates a shared pointer that manages a new object (function template)

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