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

From cppreference.com
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m (fmt.)
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{{cpp/container/{{{1|}}}/title|empty}}
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{{#vardefine:cont|{{{1|stack}}}}}<!--
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{{cpp/container/{{{1|}}}/navbar}}
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-->{{cpp/container/{{#var:cont}}/title|empty}}
 +
{{cpp/container/{{#var:cont}}/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{#switch:{{{1|}}}
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{{#switch:{{#var:cont}}
 
|flat_set|flat_multiset|flat_map|flat_multimap=
 
|flat_set|flat_multiset|flat_map|flat_multimap=
 
{{dcl|since=c++23|
 
{{dcl|since=c++23|
 
bool empty() const noexcept;
 
bool empty() const noexcept;
 
}}
 
}}
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|{{dcl|since={{cpp/std|{{{1|}}}}}|
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|{{dcl|since={{cpp/std|{{#var:cont}}}}|
 
bool empty() const;
 
bool empty() const;
 
}}
 
}}
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{{dcl end}}
 
{{dcl end}}
  
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{{#switch:{{{1|}}}
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{{#switch:{{#var:cont}}
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|flat_map|flat_multimap
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|flat_map|flat_multimap=
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=Checks if the underlying containers have no elements. Equivalent to {{c|1=return begin() == end();}}.
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Checks if the underlying containers have no elements. Equivalent to: {{c|1=return begin() == end();}}.
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|flat_set|flat_multiset
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|flat_set|flat_multiset=
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=Checks if the underlying container has no elements. Equivalent to {{c|1=return begin() == end();}}.
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Checks if the underlying container has no elements. Equivalent to: {{c|1=return begin() == end();}}.
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<!--stack, queue, priority_queue:-->
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|<!--stack|queue|priority_queue=-->
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|Checks if the underlying container has no elements. Equivalent to {{c|return c.empty();}}.
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Checks if the underlying container has no elements. Equivalent to: {{box|{{c/core|return}}{{nbspt}}{{rlpt|/#Member objects|c}}{{c/core|.empty()}}}}.
 
}}
 
}}
  
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===Return value===
 
===Return value===
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{{#switch:{{{1|}}}
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{{#switch:{{#var:cont}}
 
|flat_map|flat_multimap
 
|flat_map|flat_multimap
 
={{c|true}} if the underlying containers are empty, {{c|false}} otherwise.
 
={{c|true}} if the underlying containers are empty, {{c|false}} otherwise.
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===Example===
 
===Example===
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{{#vardefine:id|{{cpp/container/get header|{{{1|}}}}}}}
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{{#vardefine:id|{{cpp/container/get header|{{#var:cont}}}}}}
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{{#switch:{{{1|}}}
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{{#switch:{{#var:cont}}
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|flat_set|flat_multiset={{include|cpp/container/set/example empty|{{{1|}}}}}
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|flat_set|flat_multiset={{include|cpp/container/set/example empty|{{#var:cont}}}}
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|flat_map|flat_multimap={{include|cpp/container/map/example empty|{{{1|}}}}}
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|flat_map|flat_multimap={{include|cpp/container/map/example empty|{{#var:cont}}}}
 
|
 
|
 
{{example
 
{{example
 
|code=
 
|code=
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#include <algorithm>
 
 
#include <iostream>
 
#include <iostream>
 
#include <{{#var:id}}>
 
#include <{{#var:id}}>
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     std::cout << std::boolalpha;
 
     std::cout << std::boolalpha;
  
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     std::{{{1|}}}<int> {{#var:id}};
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     std::{{#var:cont}}<int> {{#var:id}};
  
 
     std::cout << "Initially, {{#var:id}}.empty(): " << {{#var:id}}.empty() << '\n';
 
     std::cout << "Initially, {{#var:id}}.empty(): " << {{#var:id}}.empty() << '\n';
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===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{dsc inc|cpp/container/dsc size|{{{1|}}}}}
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{{dsc inc|cpp/container/dsc size|{{#var:cont}}}}
 
{{dsc inc|cpp/iterator/dsc empty}}
 
{{dsc inc|cpp/iterator/dsc empty}}
 
{{dsc end}}
 
{{dsc end}}

Revision as of 17:49, 1 November 2024

 
C++
 
Containers library
 
std::stack
 
bool empty() const;

Checks if the underlying container has no elements. Equivalent to: return c.empty().

Contents

Parameters

(none)

Return value

true if the underlying container is empty, false otherwise.

Complexity

Constant.

Example

Run this code
#include <iostream>
#include <stack>
 
int main()
{
    std::cout << std::boolalpha;
 
    std::stack<int> stack;
 
    std::cout << "Initially, stack.empty(): " << stack.empty() << '\n';
 
    stack.push(42);
    std::cout << "After adding elements, stack.empty(): " << stack.empty() << '\n';
}

Output: 

Initially, stack.empty(): true
After adding elements, stack.empty(): false

See also

 returns the number of elements
(public member function of std::stack<T,Container>) [edit]
(C++17)
 checks whether the container is empty
(function template) [edit]
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