std::set<Key,Compare,Allocator>::set
From cppreference.com
| (1) | ||
set();
|
(until C++11) | |
set()
: set(Compare()) {}
|
(since C++11) | |
explicit set( const Compare& comp,
const Allocator& alloc = Allocator() );
|
(2) | |
explicit set( const Allocator& alloc );
|
(3) | (since C++11) |
template< class InputIt >
set( InputIt first, InputIt last,
const Compare& comp = Compare(),
const Allocator& alloc = Allocator() );
|
(4) | |
template< class InputIt >
set( InputIt first, InputIt last,
const Allocator& alloc )
: set(first, last, Compare(), alloc) {}
|
(5) | (since C++14) |
set( const set& other );
|
(6) | |
set( const set& other, const Allocator& alloc );
|
(7) | (since C++11) |
set( set&& other );
|
(8) | (since C++11) |
set( set&& other, const Allocator& alloc );
|
(9) | (since C++11) |
set( std::initializer_list<value_type> init,
const Compare& comp = Compare(),
const Allocator& alloc = Allocator() );
|
(10) | (since C++11) |
set( std::initializer_list<value_type> init,
const Allocator& alloc )
: set(init, Compare(), alloc) {}
|
(11) | (since C++14) |
template< container-compatible-range<value_type> R >
set( std::from_range_t, R&& rg,
const Compare& comp = Compare(),
const Allocator& alloc = Allocator() );
|
(12) | (since C++23) |
template< container-compatible-range<value_type> R >
set( std::from_range_t, R&& rg,
const Allocator& alloc )
: set(std::from_range, std::forward<R>(rg), Compare(), alloc) {}
|
(13) | (since C++23) |
Constructs new container from a variety of data sources and optionally using user supplied allocator alloc or comparison function object comp.
1-3) Constructs an empty container.
4,5) Constructs the container with the contents of the range
[first, last). If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844). If
[first, last) is not a valid range, the behavior is undefined.6,7) Copy constructor. Constructs the container with the copy of the contents of
other.
|
If |
(since C++11) |
|
During class template argument deduction, only the first argument contributes to the deduction of the container's |
(since C++23) |
8,9) 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.
|
During class template argument deduction, only the first argument contributes to the deduction of the container's |
(since C++23) |
10,11) Initializer-list constructor. Constructs the container with the contents of the initializer list
init.If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).12,13) Constructs the container with the contents of
rg. If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).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 pair of iterators defining the source range of elements to copy |
| 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 |
| rg | - | a container compatible range, that is, an input_range whose elements are convertible to value_type
|
| Type requirements | ||
-InputIt must meet the requirements of LegacyInputIterator.
| ||
-Compare must meet the requirements of Compare.
| ||
-Allocator must meet the requirements of Allocator.
| ||
Complexity
1-3) Constant.
4,5) N·log(N) where N is
std::distance(first, last) in general, linear in N if [first, last) is already sorted by value_comp().6,7) Linear in size of
other.8,9) Constant. If
alloc is given and alloc != other.get_allocator(), then linear.10,11) N·log(N) where N is
init.size() in general, linear in N if init is already sorted by value_comp().12,13) N·log(N) where N is
ranges::distance(rg) in general, linear in N if rg is already sorted by value_comp().Exceptions
Calls to Allocator::allocate may throw.
Notes
After container move construction (overload (8,9)), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in [container.reqmts]/67, and a more direct guarantee is under consideration via LWG issue 2321.
Although not formally required until C++23, some implementations has already put the template parameter Allocator into non-deduced contexts in earlier modes.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_containers_ranges |
202202L |
(C++23) | Ranges-aware construction and insertion; overloads (12,13) |
Example
Run this code
#include <cmath>
#include <iostream>
#include <set>
#include <string>
struct Point { double x, y; };
struct PointCmp
{
bool operator()(const Point& lhs, const Point& rhs) const
{
return std::hypot(lhs.x, lhs.y) < std::hypot(rhs.x, rhs.y);
}
};
std::ostream& operator<<(std::ostream& os, Point pt)
{
return os << '(' << pt.x << ',' << pt.y << ')';
}
void println(auto rem, const auto& seq)
{
std::cout << rem << '{';
for (auto n{seq.size()}; const auto& elm : seq)
std::cout << elm << (--n ? ", " : "");
std::cout << "}\n";
}
int main()
{
// (1) Default constructor
std::set<std::string> a;
a.insert("horse");
a.insert("cat");
a.insert("dog");
println("1) a: ", a);
// (4) Range constructor
std::set<std::string> b(a.find("dog"), a.end());
println("2) b: ", b);
// (6) Copy constructor
std::set<std::string> c(a);
c.insert("another horse");
println("3) c: ", c);
// (8) Move constructor
std::set<std::string> d(std::move(a));
println("4) d: ", d);
println("5) a: ", a);
// (10) Initializer list constructor
std::set<std::string> e{"one", "two", "three", "five", "eight"};
println("6) e: ", e);
// Custom comparison
std::set<Point, PointCmp> f = {{2, 5}, {3, 4}, {1, 1}};
f.insert({1, -1}); // This fails because the magnitude of (1,-1) equals (1,1)
println("7) f: ", f);
// (12) Range constructor
const auto w = {"Eurybia", "Theia", "Rhea", "Aura", "Mnemosyne", "Mnemosyne"};
#if __cpp_lib_containers_ranges
std::set<std::string> g(std::from_range, w); // overload (12)
#else
std::set<std::string> g(w.begin(), w.end()); // fallback to (4)
#endif
println("8) g: ", g);
}
Possible output:
1) a: {cat, dog, horse}
2) b: {dog, horse}
3) c: {another horse, cat, dog, horse}
4) d: {cat, dog, horse}
5) a: {}
6) e: {eight, five, one, three, two}
7) f: {(1,1), (3,3), (2,2)}
8) g: {Aura, Eurybia, Mnemosyne, Rhea, Theia}
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2076 | C++11 | overload (4) conditionally required Key to be CopyInsertable into *this
|
not required |
| LWG 2193 | C++11 | the default constructor was explicit | made non-explicit |