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std::{{{1}}}::{{{1}}}

من cppreference.com
(1)
explicit {{{1}}}( const Compare& comp = Compare(),
                  const Allocator& alloc = Allocator() );
قالب:mark since none
قالب:mark until c++14
{{{1}}}() : {{{1}}}( Compare() ) {}

explicit {{{1}}}( const Compare& comp,

                  const Allocator& alloc = Allocator() );
قالب:mark since c++14
explicit {{{1}}}( const Allocator& alloc );
(1) (since C++11)
(2)
template< class InputIterator >

{{{1}}}( InputIterator first, InputIterator last,
         const Compare& comp = Compare(),

         const Allocator& alloc = Allocator() );
قالب:mark since none
template< class InputIterator >

{{{1}}}( InputIterator first, InputIterator last,

         const Allocator& alloc );
قالب:mark since c++14
{{{1}}}( const {{{1}}}& other );
(3) قالب:mark since none
{{{1}}}( const {{{1}}}& other, const Allocator& alloc );
(3) (since C++11)
{{{1}}}( {{{1}}}&& other );
(4) (since C++11)
{{{1}}}( {{{1}}}&& other, const Allocator& alloc );
(4) (since C++11)
(5)
{{{1}}}( std::initializer_list<value_type> init,

         const Compare& comp = Compare(),

         const Allocator& alloc = Allocator() );
(since C++11)
{{{1}}}( std::initializer_list<value_type> init,
         const Allocator& );
قالب:mark 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) 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) Constructs the container with the contents of the initializer list ‎init‎.

محتويات

[تعديل] 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

قالب:par hreq قالب:par req concept قالب:par req concept قالب:par req concept

[تعديل] 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()‎.

[تعديل] Example

#include <iostream>
#include <string>
#include <iomanip>
#include <map>
 
// helper function templates for printing each element
template<typename CharT, typename Traits, typename T>
void print_item(std::basic_ostream<CharT, Traits>& stream, const T& item)
{
  stream << item;
}
 
template<typename CharT, typename Traits, typename Alloc>
void print_item(std::basic_ostream<CharT, Traits>& stream,
    const std::basic_string<CharT, Traits, Alloc>& item)
{
  stream << std::quoted(item);
}
 
// A printer for unordered maps
template<typename Key, typename T, typename Compare, typename Allocator>
std::ostream& operator<<(std::ostream& stream,
    const std::map<Key, T, Compare, Allocator>& map)
{
  stream << '{';
  char comma[3] = {'\0', ' ', '\0'};
  for (const auto& pair : map) {
    stream << comma;
    print_item(stream, pair.first);
    stream << ':';
    print_item(stream, pair.second);
    comma[0] = ',';
  }
  stream << '}';
  return stream;
}
 
int main()
{
  // (1) Default constructor
  std::map<std::string, int> map1;
  map1["something"] = 69;
  map1["anything"] = 199;
  map1["that thing"] = 50;
  std::cout << std::string(80, '-') << '\n';
  std::cout << "map1 = " << map1 << '\n';
 
  // (2) Iterator constructor
  std::map<std::string, int> iter(map1.find("anything"), map1.end());
  std::cout << std::string(80, '-') << '\n';
  std::cout << "iter = " << iter << '\n';
  std::cout << "map1 = " << map1 << '\n';
 
  // (3) Copy constructor
  std::map<std::string, int> copied(map1);
  std::cout << std::string(80, '-') << '\n';
  std::cout << "copied = " << copied << '\n';
  std::cout << "map1 = " << map1 << '\n';
 
  // (4) Move constructor
  std::map<std::string, int> moved(std::move(map1));
  std::cout << std::string(80, '-') << '\n';
  std::cout << "moved = " << moved << '\n';
  std::cout << "map1 = " << map1 << '\n';
 
  // (5) Initializer list constructor
  const std::map<std::string, int> init {
    {"this", 100},
    {"can", 100},
    {"be", 100},
    {"const", 100},
  };
  std::cout << std::string(80, '-') << '\n';
  std::cout << "init = " << init << '\n';
}

الخرج:

--------------------------------------------------------------------------------
map1 = {"anything":199, "something":69, "that thing":50}
--------------------------------------------------------------------------------
iter = {"anything":199, "something":69, "that thing":50}
map1 = {"anything":199, "something":69, "that thing":50}
--------------------------------------------------------------------------------
copied = {"anything":199, "something":69, "that thing":50}
map1 = {"anything":199, "something":69, "that thing":50}
--------------------------------------------------------------------------------
moved = {"anything":199, "something":69, "that thing":50}
map1 = {}
--------------------------------------------------------------------------------
init = {"be":100, "can":100, "const":100, "this":100}

[تعديل] See also

قالب:dsc mem fun