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

From cppreference.com
(empty on arrays is a peculiar concept)
m (+inplace_vector.)
 
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{{cpp/container/{{{1|}}}/title | empty}}
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{{#vardefine:cont|{{{1|}}}}}<!--
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{{cpp/container/{{{1|}}}/navbar}}
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-->{{cpp/container/{{#var:cont}}/title|empty}}
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{{ddcl | notes={{cpp/container/mark since c++11 | {{{1|}}} }} |
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{{cpp/container/{{#var:cont}}/navbar}}
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{{#ifeq:{{{1|}}}|array|constexpr bool empty();|bool empty() const;}}
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{{dcl begin}}
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{{#switch:{{#var:cont}}
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|array=
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{{dcl|since=c++11|
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constexpr bool empty() const noexcept;
 
}}
 
}}
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Checks if the container has no elements, i.e. whether {{c|begin() {{==}} end()}}.
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|vector=
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{{dcla|anchor=no|noexcept=c++11|constexpr=c++20|
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bool empty() const;
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}}
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|inplace_vector=
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{{dcl|anchor=no|since=c++26|
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constexpr bool empty() const noexcept;
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}}
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|list|deque|set|map|multiset|multimap=
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{{dcla|anchor=no|noexcept=c++11|
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bool empty() const;
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}}
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|
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{{dcl|since={{cpp/std|{{#var:cont}}}}|
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bool empty() const noexcept;
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}}
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}}
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{{dcl end}}
 +
 
 +
Checks if the container has no elements, i.e. whether {{c|1=begin() == end()}}.
  
 
===Parameters===
 
===Parameters===
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===Return value===
 
===Return value===
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{{c|true}} if the container is empty, {{c|false}} otherwise
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{{c|true}} if the container is empty, {{c|false}} otherwise.
−
 
+
−
===Exceptions===
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−
{{noexcept}}
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===Complexity===
 
===Complexity===
−
Constant
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Constant.
  
 
===Example===
 
===Example===
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{{example
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{{#switch:{{#var:cont}}
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| The following code uses {{tt|empty}} to check if a {{c|std::{{{1}}}<int>}} contains any elements:
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|set|multiset|unordered_set|unordered_multiset
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| code=
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={{include|cpp/container/set/example_empty|{{#var:cont}}}}
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#include <{{{1}}}>
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|map|multimap|unordered_map|unordered_multimap
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#include <iostream>
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={{include|cpp/container/map/example_empty|{{#var:cont}}}}
−
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|{{include|cpp/container/{{#var:cont}}/example_empty}}
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int main()
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−
{
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    {{#ifeq: {{{1|}}} | array
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|std::array<int, 4> numbers {3, 1, 4, 1};
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    std::array<int, 0> no_numbers;
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−
 
+
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    std::cout << "numbers.empty(): " << numbers.empty() << '\n';
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    std::cout << "no_numbers.empty(): " << no_numbers.empty() << '\n';
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|std::{{{1}}}<int> numbers;
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    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
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−
 
+
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    numbers.push_back(42);
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    numbers.push_back(13317);
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    std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
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}}
 
}}
−
}
 
−
| output=
 
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{{#ifeq: {{{1|}}} | array
 
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|numbers.empty(): 0
 
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no_numbers.empty(): 1
 
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|Initially, numbers.empty(): 1
 
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After adding elements, numbers.empty(): 0
 
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}}
 
−
}}
 
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{{#ifeq: {{{1|}}} | forward_list||
 
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===See also===
 
  
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{{dcl list begin}}
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===See also===
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{{dcl list template | cpp/container/dcl list size |{{{1|}}}}}
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{{dsc begin}}
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{{dcl list end}}
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{{#switch:{{#var:cont}}
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|forward_list=
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{{dsc inc|cpp/iterator/dsc distance}}
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|
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{{dsc inc|cpp/container/dsc size|{{#var:cont}}}}
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{{dsc inc|cpp/iterator/dsc empty}}
 
}}
 
}}
 +
{{dsc end}}

Latest revision as of 00:05, 13 August 2024

 
C++
 
Containers library
 
bool empty() const noexcept;
 (since {std})

Checks if the container has no elements, i.e. whether begin() == end().

Contents

[edit] Parameters

(none)

[edit] Return value

true if the container is empty, false otherwise.

[edit] Complexity

Constant.

[edit] Example

Templated content.
The link is cpp/container/<PP>/example_empty

[edit] See also

 returns the number of elements
(public member function of std::{{{1}}}) [edit]
(C++17)
 checks whether the container is empty
(function template) [edit]
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