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std::set::set

(1)
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explicit set( const Compare& comp = Compare(),
              const Allocator& alloc = Allocator() );
 (until C++14)
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set() : set( Compare() ) {}
explicit set( const Compare& comp,
              const Allocator& alloc = Allocator() );
 (since C++14)
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explicit set( const Allocator& alloc );
 (1) (since C++11)
(2)
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template< class InputIt >
set( InputIt first, InputIt last,
     const Compare& comp = Compare(),
     const Allocator& alloc = Allocator() );
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template< class InputIt >
set( InputIt first, InputIt last, const Allocator& alloc)
    : set(first, last, Compare(), alloc) {}
 (since C++14)
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set( const set& other );
 (3)
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set( const set& other, const Allocator& alloc );
 (3) (since C++11)
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set( set&& other );
 (4) (since C++11)
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set( set&& other, const Allocator& alloc );
 (4) (since C++11)
(5)
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set( std::initializer_list<value_type> init,
     const Compare& comp = Compare(),
     const Allocator& alloc = Allocator() );
 (since C++11)
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set( std::initializer_list<value_type> init, const Allocator& alloc )
    : set(init, Compare(), alloc) {}
 (since C++14)

Constructs new container from a variety of data sources and optionally using user supplied allocator alloc or comparison function object comp.

1) Default constructor. Constructs empty container.
2) Range constructor. Constructs the container with the contents of the range [first, last).
3) Copy constructor. Constructs the container with the copy of the contents of other. If alloc is not provided, allocator is obtained by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction(other.get_allocator()).
4) Move constructor. Constructs the container with the contents of other using move semantics. If alloc is not provided, allocator is obtained by move-construction from the allocator belonging to other.
5) Initializer-list constructor. Constructs the container with the contents of the initializer list init.

Parameters

alloc - allocator to use for all memory allocations of this container
comp - comparison function object to use for all comparisons of keys
first, last - the range to copy the elements from
other - another container to be used as source to initialize the elements of the container with
init - initializer list to initialize the elements of the container with
Type requirements
- InputIt must meet the requirements of InputIterator.
- Compare must meet the requirements of Compare.
- Allocator must meet the requirements of Allocator.

Complexity

1) Constant.

2) N log(N) where N = std::distance(first, last) in general, linear in N if the range is already sorted by value_comp().

3) Linear in size of other.

4) Constant. If alloc is given and alloc != other.get_allocator(), then linear.

5) N log(N) where N = init.size()) in general, linear in N if init is already sorted by value_comp().

Example

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#include <iostream>
#include <string>
#include <set>
  
// Helper function for printing pairs.
template<class Ch, class Tr, class A, class B> inline
std::basic_ostream<Ch, Tr>& operator<<(std::basic_ostream<Ch, Tr>& stream, std::pair<A,B> p)
{
  return stream << '(' << p.first << ", " << p.second << ')';
}
  
// Helper function for printing containers.
template<class Ch, class Tr, class Co>
std::basic_ostream<Ch, Tr>& operator<<(std::basic_ostream<Ch, Tr>& stream, Co& c)
{
  stream << '{' << *c.begin();
  
  for(auto it = ++(c.begin()); it != c.end(); ++it)
    stream << ", " << *it;
  
  stream << '}' << std::endl;
  return stream;
}
  
int main()
{
  // (1) Default constructor
  std::set<std::string> a;
  a.insert("something");
  a.insert("anything");
  a.insert("that thing");
  std::cout << "a = " << a;
  
  // (2) Iterator constructor
  std::set<std::string> b(a.find("anything"), a.end());
  std::cout << std::string(80, '-') << std::endl;
  std::cout << "b = " << b;
  
  // (3) Copy constructor
  std::set<std::string> c(a);
  c.insert("another thing");
  std::cout << std::string(80, '-') << std::endl;
  std::cout << "a = " << a;
  std::cout << "c = " << c;
  
  // (4) Move constructor
  std::set<std::string> d(std::move(a));
  std::cout << std::string(80, '-') << std::endl;
  std::cout << "a = nullptr" << std::endl;
  std::cout << "d = " << d;
  
  // (5) Initializer list constructor
  std::set<std::string> e{
    "one", "two", "three", "five", "eight"
  };
  std::cout << std::string(80, '-') << std::endl;
  std::cout << "e = " << e;
}

Output:

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a = {anything, something, that thing}
--------------------------------------------------------------------------------
b = {anything, something, that thing}
--------------------------------------------------------------------------------
a = {anything, something, that thing}
c = {another thing, anything, something, that thing}
--------------------------------------------------------------------------------
a = nullptr
d = {anything, something, that thing}
--------------------------------------------------------------------------------
e = {eight, five, one, three, two}

See also

operator=
assigns values to the container
(public member function)
doc_CPP
doc_CPP
2025-01-10 15:47:30
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