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C++ set constructor

There are following five uses of set constructor:

  1. default constructor: This is used to construct an empty set container with zero elements.
  2. range constructor: This is used to construct a container with the contents of range [first, last).
  3. copy constructor: This is used to construct a set with a copy of the elements of existing container.
  4. move constructor: This is used to construct the container with the elements of other with the use of move semantics.
  5. initializer list constructor: This is used to construct the set with the contents of the initializer list.

Syntax

Default constructor

range constructor

copy constructor

move constructor

initializer list constructor

Parameter

comp: A comparison function object which takes two key arguments and returns true if first argument goes before the second argument otherwise false. By default it uses less<key_type> predicate.

alloc: A allocator object use for all memory allocations of this container.

first: Input iterator to the first position in a range.

last: Input iterator to the last position in a range.

x: Another set object of the same type.

il: An initializer list object from which the elements are to be copied.

Return value

Constructor never returns any value.

Complexity

For empty constructors and move constructors complexity will be constant.

For all other cases, complexity will be linear in the distance between the iterators if the elements are already sorted.

Iterator validity

Invalidate all pointers, iterators, and references related to x if the elements of set container are moved in the move constructor.

Data Races

All copied elements are accessed.

Exception Safety

No effects in case an exception is thrown.

Example 1

Let's see the simple example for default constructor:

Output:

Size of set = 0

In the above example, s is an empty set therefore, size is 0.

Example 2

Let's see a simple example for range constructor:

Output:

Size of set container myset is: 5

In the above example, set myset is constructed with the elements of evens.

Example 3

Let's see a simple example for copy constructor:

Output:

Size of set container s1 is : 2
Size of new set container s2 is : 2

In the above example, s2 is a copy of s1 set.

Example 4

Let's see a simple example for move constructor:

Output:

Size of set container s1 is : 2
Size of new set container s2 is : 2

In the above example, contents of s1 are moved to s2 set.

Example 5

Let's see a simple example for initializer list constructor:

Output:

Size of set container fruit is : 5

The above example creates a set fruit with string as key and initializes it with initializer_list.


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