std::make_unique,std::make_unique_default_init (3) - Linux Manuals

std::make_unique,std::make_unique_default_init: std::make_unique,std::make_unique_default_init

NAME

std::make_unique,std::make_unique_default_init - std::make_unique,std::make_unique_default_init

Synopsis

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