std::deque::deque(3)

NAME
std::deque::deque - std::deque::deque

Synopsis
   deque(); (1)
   explicit deque( const Allocator& alloc ); (2)
   explicit deque( size_type count,
                   const T& value = T(), (until C++11)
                   const Allocator& alloc =
   Allocator() );
   deque( size_type count,
          const T& value, (since C++11)
          const Allocator& alloc = Allocator() );
   explicit deque( size_type count ); (since C++11)
                        (until C++14)
   explicit deque( size_type count,
                   const Allocator& alloc = (since C++14)
   Allocator() );
   template< class InputIt > (3)
   deque( InputIt first, InputIt last, (5)
          const Allocator& alloc = Allocator() );
   deque( const deque& other ); (4) (6)
   deque( const deque& other, const Allocator& (7) (since C++11)
   alloc );
   deque( deque&& other ); (8) (since C++11)
   deque( deque&& other, const Allocator& alloc ); (9) (since C++11)
   deque( std::initializer_list<T> init, (10) (since C++11)
          const Allocator& alloc = Allocator() );
   template< container-compatible-range<T> R >
   deque( std::from_range_t, R&& rg, (11) (since C++23)
          const Allocator& alloc = Allocator() );
   Constructs a new container from a variety of data sources, optionally using a user
   supplied allocator alloc.
   1) Default constructor. Constructs an empty container with a default-constructed
   allocator.
   2) Constructs an empty container with the given allocator alloc.
   3) Constructs the container with count copies of elements with value value.
   4) Constructs the container with count default-inserted instances of T. No copies
   are made.
   5) Constructs the container with the contents of the range [first, last).
   This constructor has the same effect as
   deque(static_cast<size_type>(first), static_cast<value_type>(last), a) (until C++11)
   if InputIt is an integral type.
   This overload participates in overload resolution only if InputIt
   satisfies LegacyInputIterator, to avoid ambiguity with the overload (since C++11)
   (3).
   6) Copy constructor. Constructs the container with the copy of the contents of
   other.
   The allocator is obtained as if by calling (since
   std::allocator_traits<allocator_type>::select_on_container_copy_construction( C++11)
       other.get_allocator()).
   7) Constructs the container with the copy of the contents of other, using alloc as
   the allocator.
   During class template argument deduction, only the first argument
   contributes to the deduction of the container's Allocator template (since C++23)
   parameter.
   8) Move constructor. Constructs the container with the contents of other using move
   semantics. Allocator is obtained by move-construction from the allocator belonging
   to other.
   9) Allocator-extended move constructor. Using alloc as the allocator for the new
   container, moving the contents from other; if alloc != other.get_allocator(), this
   results in an element-wise move.
   During class template argument deduction, only the first argument
   contributes to the deduction of the container's Allocator template (since C++23)
   parameter.
   10) Constructs the container with the contents of the initializer list init.
   11) Constructs the container with the contents of the range rg.

Parameters
   alloc - allocator to use for all memory allocations of this container
   count - the size of the container
   value - the value to initialize elements of the container with
   first, last - the range [first, last) 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
   rg - a container compatible range, that is, an input_range whose elements
                 are convertible to T

Complexity
   1,2) Constant.
   3,4) Linear in count.
   5) Linear in distance between first and last.
   6,7) Linear in size of other.
   8) Constant.
   9) Linear if alloc != other.get_allocator(), otherwise constant.
   10) Linear in size of init.
   11) Linear in ranges::distance(rg).

Exceptions
   Calls to Allocator::allocate may throw.

Notes
   After container move construction (overload (8)), 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.
       Feature-test macro Value Std Feature
   __cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion;
                        overload (11)

Example
// Run this code
 #include <iostream>
 #include <string>
 #include <deque>
 template<typename T>
 std::ostream& operator<<(std::ostream& s, const std::deque<T>& v)
 {
     s.put('{');
     for (char comma[]{'\0', ' ', '\0'}; const auto& e : v)
         s << comma << e, comma[0] = ',';
     return s << "}\n";
 }
 int main()
 {
     // C++11 initializer list syntax:
     std::deque<std::string> words1{"the", "frogurt", "is", "also", "cursed"};
     std::cout << "1: " << words1;
     // words2 == words1
     std::deque<std::string> words2(words1.begin(), words1.end());
     std::cout << "2: " << words2;
     // words3 == words1
     std::deque<std::string> words3(words1);
     std::cout << "3: " << words3;
     // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"}
     std::deque<std::string> words4(5, "Mo");
     std::cout << "4: " << words4;
     auto const rg = {"cat", "cow", "crow"};
 #ifdef __cpp_lib_containers_ranges
     std::deque<std::string> words5(std::from_range, rg); // overload (11)
 #else
     std::deque<std::string> words5(rg.begin(), rg.end()); // overload (5)
 #endif
     std::cout << "5: " << words5;
 }

Output:
 1: {the, frogurt, is, also, cursed}
 2: {the, frogurt, is, also, cursed}
 3: {the, frogurt, is, also, cursed}
 4: {Mo, Mo, Mo, Mo, Mo}
 5: {cat, cow, crow}
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       the complexity requirement of
   LWG 144 C++98 overload (5) was the same changed to linear complexity
                       as that of the corresponding
                       overload of std::vector
                       the complexity requirement of changed to linear in
   LWG 237 C++98 overload std::distance(first, last)
                       (5) was linear in first - last
                       for overload (4), the elements in
   LWG 868 C++98 the container were default they are value-initialized
                       constructed
   LWG 2193 C++11 the default constructor is explicit made non-explicit

See also
   assign assigns values to the container
             (public member function)
   operator= assigns values to the container
             (public member function)