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Difference between revisions of "Template:cpp/container/push back"

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m (→‎Synopsis: +(since C++20) tags to *)
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{{cpp/container/{{{1|}}}/title|push_back}}
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{{#vardefine:cont|{{{1|vector}}}}}<!--
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{{cpp/container/{{{1|}}}/navbar}}
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-->{{cpp/container/{{#var:cont}}/title|push_back}}
 +
{{cpp/container/{{#var:cont}}/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{dcl|num=1|notes={{#ifeq:{{{1|}}}|vector|{{mark constexpr since c++20}}}}|
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{{dcl|num=1|notes={{#ifeq:{{#var:cont}}|vector|{{mark constexpr since c++20}}}}|
 
void push_back( const T& value );
 
void push_back( const T& value );
 
}}
 
}}
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{{dcl|num=2|since=c++11|notes={{#ifeq:{{{1|}}}|vector|{{mark constexpr since c++20}}}}|
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{{dcl|num=2|since=c++11|notes={{#ifeq:{{#var:cont}}|vector|{{mark constexpr since c++20}}}}|
 
void push_back( T&& value );
 
void push_back( T&& value );
 
}}
 
}}
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@2@ {{c|value}} is moved into the new element.
 
@2@ {{c|value}} is moved into the new element.
  
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{{cpp/container/note iterator invalidation|{{{1|}}}|push_back}}
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{{cpp/container/note iterator invalidation|{{#var:cont}}|push_back}}
  
 
===Parameters===
 
===Parameters===
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===Complexity===
 
===Complexity===
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{{#switch:{{{1|}}}
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{{#switch:{{#var:cont}}
 
|vector=Amortized constant.
 
|vector=Amortized constant.
 
|deque|list=Constant.
 
|deque|list=Constant.
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===Exceptions===
 
===Exceptions===
 
If an exception is thrown (which can be due to {{tt|Allocator::allocate()}} or element copy/move constructor/assignment), this function has no effect ([[cpp/language/exceptions#Exception safety|strong exception guarantee]]).
 
If an exception is thrown (which can be due to {{tt|Allocator::allocate()}} or element copy/move constructor/assignment), this function has no effect ([[cpp/language/exceptions#Exception safety|strong exception guarantee]]).
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{{#ifeq:{{{1|}}}|vector|
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{{#ifeq:{{#var:cont}}|vector|
 
{{rrev|since=c++11|
 
{{rrev|since=c++11|
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If {{tt|T}}'s move constructor is not {{c|noexcept}} and {{tt|T}} is not {{named req|CopyInsertable}} into {{c|*this}}, vector will use the throwing move constructor. If it throws, the guarantee is waived and the effects are unspecified.
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If the move constructor of {{tt|T}} is not {{c|noexcept}} and {{tt|T}} is not {{named req|CopyInsertable}} into {{c|*this}}, vector will use the throwing move constructor. If it throws, the guarantee is waived and the effects are unspecified.
 
}}
 
}}
 
<!---->
 
<!---->
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#include <iostream>
 
#include <iostream>
 
#include <string>
 
#include <string>
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#include <{{{1|list}}}>
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#include <{{#var:cont}}>
  
 
int main()
 
int main()
 
{
 
{
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     std::{{{1|list}}}<std::string> letters;
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     std::{{#var:cont}}<std::string> letters;
 
   
 
   
 
     letters.push_back("abc");
 
     letters.push_back("abc");
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     letters.push_back(std::move(s));
 
     letters.push_back(std::move(s));
  
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     std::cout << "std::{{{1|list}}} letters holds: ";
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     std::cout << "std::{{#var:cont}} letters holds: ";
 
     for (auto&& e : letters)
 
     for (auto&& e : letters)
 
         std::cout << std::quoted(e) << ' ';
 
         std::cout << std::quoted(e) << ' ';
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|p=true
 
|p=true
 
|output=
 
|output=
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std::{{{1|list}}} letters holds: "abc" "def"
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std::{{#var:cont}} letters holds: "abc" "def"
 
Moved-from string s holds: ""
 
Moved-from string s holds: ""
 
}}
 
}}
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===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{dsc inc|cpp/container/dsc emplace_back|{{{1|}}}}}
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{{dsc inc|cpp/container/dsc emplace_back|{{#var:cont}}}}
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{{#ifeq:{{{1|}}}|vector||{{dsc inc|cpp/container/dsc push_front|{{{1|}}}}}}}
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{{#ifeq:{{#var:cont}}|vector||{{dsc inc|cpp/container/dsc push_front|{{#var:cont}}}}}}
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{{dsc inc|cpp/container/dsc pop_back|{{{1|}}}}}
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{{dsc inc|cpp/container/dsc pop_back|{{#var:cont}}}}
 
{{dsc inc|cpp/iterator/dsc back_inserter}}
 
{{dsc inc|cpp/iterator/dsc back_inserter}}
 
{{dsc end}}
 
{{dsc end}}

Latest revision as of 17:47, 29 August 2024

 
C++
 
Containers library
 
std::vector
Member types
Member functions
Non-member functions
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides(C++17)
 
void push_back( const T& value );
 (1) (constexpr since C++20)
void push_back( T&& value );
 (2) (since C++11)
(constexpr since C++20)

Appends the given element value to the end of the container.

1) The new element is initialized as a copy of value.
2) value is moved into the new element.

If after the operation the new size() is greater than old capacity() a reallocation takes place, in which case all iterators (including the end() iterator) and all references to the elements are invalidated. Otherwise only the end() iterator is invalidated.

Contents

[edit] Parameters

value - the value of the element to append
Type requirements
-
T must meet the requirements of CopyInsertable in order to use overload (1).
-
T must meet the requirements of MoveInsertable in order to use overload (2).

[edit] Return value

(none)

[edit] Complexity

Amortized constant.

[edit] Exceptions

If an exception is thrown (which can be due to Allocator::allocate() or element copy/move constructor/assignment), this function has no effect (strong exception guarantee).

If the move constructor of T is not noexcept and T is not CopyInsertable into *this, vector will use the throwing move constructor. If it throws, the guarantee is waived and the effects are unspecified.

(since C++11)

Notes

Some implementations throw std::length_error when push_back causes a reallocation that exceeds max_size (due to an implicit call to an equivalent of reserve(size() + 1)).

[edit] Example

Run this code
#include <iomanip>
#include <iostream>
#include <string>
#include <vector>
 
int main()
{
    std::vector<std::string> letters;
 
    letters.push_back("abc");
    std::string s{"def"};
    letters.push_back(std::move(s));
 
    std::cout << "std::vector letters holds: ";
    for (auto&& e : letters)
        std::cout << std::quoted(e) << ' ';
 
    std::cout << "\nMoved-from string s holds: " << std::quoted(s) << '\n';
}

Possible output: 

std::vector letters holds: "abc" "def"
Moved-from string s holds: ""

[edit] See also

(C++11)
 constructs an element in-place at the end
(public member function of std::vector<T,Allocator>) [edit]
removes the last element
(public member function of std::vector<T,Allocator>) [edit]
creates a std::back_insert_iterator of type inferred from the argument
(function template) [edit]
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