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

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(use "erase" to match Erasable)
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{{cpp/container/{{{1|}}}/title | clear}}
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{{#vardefine:cont|{{{1|inplace_vector}}}}}<!--
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{{cpp/container/{{{1|}}}/navbar}}
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-->{{cpp/container/{{#var:cont}}/title|clear}}
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{{cpp/container/{{#var:cont}}/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{cpp/container/noexcept dcl|{{{1|}}}|dcl=
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{{#switch:{{#var:cont}}
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|vector=
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{{dcl|notes={{mark noexcept since c++11}}<br>{{mark constexpr since c++20}}|
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void clear();
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}}
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|inplace_vector=
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{{dcl|since=c++26|
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constexpr void clear() noexcept;
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}}
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|flat_set|flat_multiset|flat_map|flat_multimap=
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{{dcl|since=c++23|
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void clear() noexcept;
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}}
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|
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{{cpp/container/noexcept dcl|{{#var:cont}}|dcl=
 
void clear()
 
void clear()
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}}
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Erases all elements from the container. After this call, {{lc|size()}} returns zero.
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Erases all elements from the container{{cpp/container/if ad|{{#var:cont}}|{{nbsp}}adaptor}}. {{#ifeq:{{#var:cont}}|forward_list||After this call, {{lc|size()}} returns zero.}}
  
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Invalidates any references, pointers, or iterators referring to contained elements. {{#switch:{{{1|}}}|list|forward_list|map|multimap|set|multiset=Any past-the-end iterator remains valid.|vector|deque=Any past-the-end iterators are also invalidated.|unordered_map|unordered_multimap|unordered_set|unordered_multiset=May also invalidate past-the-end iterators.}}
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Invalidates any references, pointers, and iterators referring to contained elements.
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{{#ifeq: {{{1|}}} | vector | &nbsp;
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{{#switch:{{#var:cont}}
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<!--|flat_set|flat_multiset|flat_map|flat_multimap={{todo}}-->
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|list|forward_list|map|multimap|set|multiset=
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Any past-the-end iterator remains valid.
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|unordered_map|unordered_multimap|unordered_set|unordered_multiset=
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May also invalidate past-the-end iterators.
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|inplace_vector|deque=
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Any past-the-end iterators are also invalidated.
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|vector=
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Any past-the-end iterators are also invalidated.
  
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Leaves the {{lc|capacity()}} of the vector unchanged (note: the standard's restriction on the changes to capacity is in the specification of {{tt|vector::reserve}}, see [http://stackoverflow.com/a/18467916])  
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Leaves the {{lc|capacity()}} of the vector unchanged (Note: the standard's restriction on the changes to capacity is in the specification of {{lc|reserve()}}, see [https://stackoverflow.com/a/18467916 SO]).
 
}}
 
}}
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<!---->
 
===Parameters===
 
===Parameters===
 
(none)
 
(none)
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===Complexity===
 
===Complexity===
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Linear in the size of the container, i.e., the number of elements.
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Linear in the size of the container{{cpp/container/if ad|{{#var:cont}}|{{nbsp}}adaptor}}, i.e., the number of elements.
  
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{{cpp/container/if seq|{{{1|}}}|
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===Example===
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{{example
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|code=
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#include <iostream>
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#include <string_view>
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#include <{{cpp/container/get header|{{#var:cont}}}}>
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void print_info(std::string_view rem, const std::{{#var:cont}}{{cpp/container/if map|{{#var:cont}}|<int, char>|<int{{#ifeq:{{#var:cont}}|inplace_vector|, 3}}>}}& v)
 +
{
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    std::cout << rem << "{ ";
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    {{cpp/container/if map|{{#var:cont}}
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    |for (const auto& [key, value] : v)
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        std::cout << '[' << key << "]:" << value << ' ';
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    |for (const auto& value : v)
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        std::cout << value << ' ';
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    }}
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    {{#switch:{{#var:cont}}
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    |forward_list=std::cout << "}\n";
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    |vector=std::cout << "}\n";
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    std::cout << "Size=" << v.size() << ", Capacity=" << v.capacity() << '\n';
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    |#default=std::cout << "}\n";
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    std::cout << "Size=" << v.size() << '\n';}}
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}
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 +
int main()
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{
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    std::{{#var:cont}}{{cpp/container/if map|{{#var:cont}}
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    |<int, char> container{<!---->{1, 'x'}, {2, 'y'}, {3, 'z'}<!---->};
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    |<int{{#ifeq:{{#var:cont}}|inplace_vector|, 3}}> container{1, 2, 3};}}
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    print_info("Before clear: ", container);
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    container.clear();
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    print_info("After clear: ", container);
 +
}
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|p={{cpp/container/if unord|{{#var:cont}}|true|false}}
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|output=
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{{#switch:{{#var:cont}}
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|vector=
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Before clear: { 1 2 3 }
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Size=3, Capacity=3
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After clear: { }
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Size=0, Capacity=3
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|inplace_vector
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|deque
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|list
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|multiset
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|set
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|flat_set
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|flat_multiset
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|unordered_multiset
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|unordered_set=
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Before clear: { 1 2 3 }
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Size=3
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After clear: { }
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Size=0
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|forward_list=
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Before clear: { 1 2 3 }
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After clear: { }
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|map
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|multimap
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|flat_map
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|flat_multimap
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|unordered_map
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|unordered_multimap=
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Before clear: { [1]:x [2]:y [3]:z }
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Size=3
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After clear: { }
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Size=0
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}}
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}}
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<!---->
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{{#switch:{{#var:cont}}|inplace_vector|flat_map|flat_set|flat_multimap|flat_multiset=|
 
===Defect reports===
 
===Defect reports===
 
{{dr list begin}}
 
{{dr list begin}}
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{{cpp/container/if seq|{{#var:cont}}|
 
{{dr list item|wg=lwg|dr=2231|std=C++11|before=complexity guarantee was mistakenly omitted in C++11|after=complexity reaffirmed as linear}}
 
{{dr list item|wg=lwg|dr=2231|std=C++11|before=complexity guarantee was mistakenly omitted in C++11|after=complexity reaffirmed as linear}}
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{{dr list end}}
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}}<!--
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-->{{cpp/container/if ord|{{#var:cont}}|
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{{dr list item|wg=lwg|dr=224|std=C++98|before=the complexity was {{c|log(size()) + N}}, but {{c|N}} was not defined|after=corrected to 'linear in {{c|size()}}'}}
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}}<!--
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-->{{cpp/container/if unord|{{#var:cont}}|
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{{dr list item|wg=lwg|dr=2550|std=C++11|before=for unordered associative containers, unclear if complexity<br>is linear in the number of elements or buckets|after=clarified that it's linear in the number of elements}}
 
}}
 
}}
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{{cpp/container/if unord|{{{1|}}}|
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<!---->
−
===Defect reports===
+
−
{{dr list begin}}
+
−
{{dr list item|wg=lwg|dr=2550|std=C++11|before=for unordered associative containers, unclear if complexity is linear in the number of elements or buckets|after=clarified that it's linear in the number of elements}}
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{{dr list end}}
 
{{dr list end}}
 
}}
 
}}
−
 
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<!---->
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{#ifeq: {{{1|}}} | forward_list
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{{#ifeq:{{#var:cont}}|forward_list
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| {{dsc inc | cpp/container/dsc erase_after |{{{1|}}}}}
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|{{dsc inc|cpp/container/dsc erase_after|{{#var:cont}}}}
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| {{dsc inc | cpp/container/dsc erase |{{{1|}}}}}
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|{{dsc inc|cpp/container/dsc erase|{{#var:cont}}}}
 
}}
 
}}
 
{{dsc end}}
 
{{dsc end}}

Latest revision as of 09:50, 16 August 2024

 
C++
 
Containers library
 
std::inplace_vector
Member types
Member functions
Non-member functions
 
constexpr void clear() noexcept;
 (since C++26)

Erases all elements from the container. After this call, size() returns zero.

Invalidates any references, pointers, and iterators referring to contained elements. Any past-the-end iterators are also invalidated.

Contents

[edit] Parameters

(none)

[edit] Return value

(none)

[edit] Complexity

Linear in the size of the container, i.e., the number of elements.

[edit] Example

Run this code
#include <iostream>
#include <string_view>
#include <inplace_vector>
 
void print_info(std::string_view rem, const std::inplace_vector<int, 3>& v)
{
    std::cout << rem << "{ ";
    for (const auto& value : v)
        std::cout << value << ' ';
    std::cout << "}\n";
    std::cout << "Size=" << v.size() << '\n';
}
 
int main()
{
    std::inplace_vector<int, 3> container{1, 2, 3};
    print_info("Before clear: ", container);
    container.clear();
    print_info("After clear: ", container);
}

Output: 

Before clear: { 1 2 3 }
Size=3
After clear: { }
Size=0

[edit] See also

 erases elements
(public member function of std::inplace_vector<T,N>) [edit]
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