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Difference between revisions of "Template:cpp/container/constructor"

From cppreference.com
m (Text replace - "{{concept" to "{{named req")
(the "default constructor" entry is confusing as the section contains two declarations)
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{{{1}}}();
 
{{{1}}}();
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explicit {{{1}}}( const Allocator& alloc );
 
 
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{{{1}}}() noexcept(noexcept(Allocator()));
 
{{{1}}}() noexcept(noexcept(Allocator()));
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explicit {{{1}}}( const Allocator& alloc );
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explicit {{{1}}}( const Allocator& alloc ) noexcept;
 
explicit {{{1}}}( const Allocator& alloc ) noexcept;
 
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explicit {{{1}}}( const Allocator& alloc );
 
explicit {{{1}}}( const Allocator& alloc );
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{{#ifeq:{{{1}}}|forward_list
 
{{#ifeq:{{{1}}}|forward_list
 
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|{{dcl | num=2 | since=c++11 | 1=

Revision as of 12:27, 9 August 2019

 
C++
 
Containers library
 
{{{1}}}();
 (1)
explicit {{{1}}}( const Allocator& alloc );
 (1)
(2)
explicit {{{1}}}( size_type count,

                  const T& value = T(),

                  const Allocator& alloc = Allocator());
 (until C++11)
         {{{1}}}( size_type count,

                  const T& value,

                  const Allocator& alloc = Allocator());
 (since C++11)
(3)
explicit {{{1}}}( size_type count );
 (since C++11)
(until C++14)
explicit {{{1}}}( size_type count, const Allocator& alloc = Allocator() );
 (since C++14)
template< class InputIt >

{{{1}}}( InputIt first, InputIt last,

         const Allocator& alloc = Allocator() );
 (4) (since {std})
{{{1}}}( const {{{1}}}& other );
 (5) (since {std})
{{{1}}}( const {{{1}}}& other, const Allocator& alloc );
 (5) (since C++11)
{{{1}}}( {{{1}}}&& other );
 (6) (since C++11)
{{{1}}}( {{{1}}}&& other, const Allocator& alloc );
 (7) (since C++11)
{{{1}}}( std::initializer_list<T> init,
         const Allocator& alloc = Allocator() );
 (8) (since C++11)

Constructs a new container from a variety of data sources, optionally using a user supplied allocator alloc.

1) Default constructor. Constructs an empty container. If no allocator is supplied, allocator is obtained from a default-constructed instance.
2) Constructs the container with count copies of elements with value value.
3) Constructs the container with count default-inserted instances of T. No copies are made.
4) Constructs the container with the contents of the range [first, last).
This constructor has the same effect as {{{1}}}(static_cast<size_type>(first), static_cast<value_type>(last), a) if InputIt is an integral type. (until C++11)
This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator, to avoid ambiguity with the overload (2). (since C++11)
5) Copy constructor. Constructs the container with the copy of the contents of other. If alloc is not provided, allocator is obtained as if by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction(other.get_allocator()).
6) 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.
7) 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.
8) Constructs the container with the contents of the initializer list init.

Contents

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 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

Complexity

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

Exceptions

Calls to Allocator::allocate may throw.

Notes

After container move construction (overload (6)), 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.


Example

Run this code
#include <{{{1}}}>
#include <string>
#include <iostream>
 
template<typename T>
std::ostream& operator<<(std::ostream& s, const std::{{{1}}}<T>& v) {
    s.put('[');
    char comma[3] = {'\0', ' ', '\0'};
    for (const auto& e : v) {
        s << comma << e;
        comma[0] = ',';
    }
    return s << ']';
}
 
int main() 
{
    // c++11 initializer list syntax:
    std::{{{1}}}<std::string> words1 {"the", "frogurt", "is", "also", "cursed"};
    std::cout << "words1: " << words1 << '\n';
 
    // words2 == words1
    std::{{{1}}}<std::string> words2(words1.begin(), words1.end());
    std::cout << "words2: " << words2 << '\n';
 
    // words3 == words1
    std::{{{1}}}<std::string> words3(words1);
    std::cout << "words3: " << words3 << '\n';
 
    // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"}
    std::{{{1}}}<std::string> words4(5, "Mo");
    std::cout << "words4: " << words4 << '\n';
}

Output: 

words1: [the, frogurt, is, also, cursed]
words2: [the, frogurt, is, also, cursed]
words3: [the, frogurt, is, also, cursed]
words4: [Mo, Mo, Mo, Mo, Mo]

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 2193 C++11 the default constructor is explicit made non-explicit

See also

 assigns values to the container
(public member function of std::{{{1}}}) [edit]
assigns values to the container
(public member function of std::{{{1}}}) [edit]
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