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

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m (Shorten template names. Use {{lc}} where appropriate.)
m (Hide DR-section on inplace_vector::clear page.)
 
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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}}
−
{{ddcl | notes={{cpp/container/mark since c++11 | {{{1|}}} }} |
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{{cpp/container/{{#var:cont}}/navbar}}
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{{dcl begin}}
 +
{{#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}}|
 
void clear();
 
void clear();
 
}}
 
}}
 +
|inplace_vector=
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{{dcl|since=c++26|
 +
constexpr void clear() noexcept;
 +
}}
 +
|flat_set|flat_multiset|flat_map|flat_multimap=
 +
{{dcl|since=c++23|
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void clear() noexcept;
 +
}}
 +
|
 +
{{cpp/container/noexcept dcl|{{#var:cont}}|dcl=
 +
void clear()
 +
}}
 +
}}
 +
{{dcl end}}
  
−
Removes all elements from the container. {{#ifeq: {{{1|}}} | vector | The allocated memory will not be released, effectively leaving the {{rlpt|capacity}} of the vector unchanged.}} The past-the-end iterators are not invalidated.
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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.}}
  
 +
Invalidates any references, pointers, and iterators referring to contained elements.
 +
{{#switch:{{#var:cont}}
 +
<!--|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.
 +
 +
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]).
 +
}}
 +
<!---->
 
===Parameters===
 
===Parameters===
 
(none)
 
(none)
Line 12: Line 45:
 
===Return value===
 
===Return value===
 
(none)
 
(none)
−
 
−
===Exceptions===
 
−
{{noexcept}}
 
  
 
===Complexity===
 
===Complexity===
−
linear in the size of the container.
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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.
−
{{cpp/container/if seq|{{{1|}}}|
+
−
{{rev list begin}}
+
−
{{rev list item |
+
−
{{tt|clear}} is defined in terms of {{tt|erase}}, which has linear complexity.
+
−
| {{mark until c++11}} }}
+
−
{{rev list item |
+
−
{{tt|clear}} is not defined in terms of {{tt|erase}}, but [http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#2231 LWG 2231] proposes to define {{tt|clear}} to have linear complexity for sequence containers.
+
−
| {{mark since c++11}} }}
+
−
{{rev list end}} }}
+
  
 +
===Example===
 +
{{example
 +
|code=
 +
#include <iostream>
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#include <string_view>
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#include <{{cpp/container/get header|{{#var:cont}}}}>
 +
 +
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)
 +
{
 +
    std::cout << rem << "{ ";
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    {{cpp/container/if map|{{#var:cont}}
 +
    |for (const auto& [key, value] : v)
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        std::cout << '[' << key << "]:" << value << ' ';
 +
    |for (const auto& value : v)
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        std::cout << value << ' ';
 +
    }}
 +
    {{#switch:{{#var:cont}}
 +
    |forward_list=std::cout << "}\n";
 +
    |vector=std::cout << "}\n";
 +
    std::cout << "Size=" << v.size() << ", Capacity=" << v.capacity() << '\n';
 +
    |#default=std::cout << "}\n";
 +
    std::cout << "Size=" << v.size() << '\n';}}
 +
}
 +
 +
int main()
 +
{
 +
    std::{{#var:cont}}{{cpp/container/if map|{{#var:cont}}
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    |<int, char> container{<!---->{1, 'x'}, {2, 'y'}, {3, 'z'}<!---->};
 +
    |<int{{#ifeq:{{#var:cont}}|inplace_vector|, 3}}> container{1, 2, 3};}}
 +
    print_info("Before clear: ", container);
 +
    container.clear();
 +
    print_info("After clear: ", container);
 +
}
 +
|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
 +
|deque
 +
|list
 +
|multiset
 +
|set
 +
|flat_set
 +
|flat_multiset
 +
|unordered_multiset
 +
|unordered_set=
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Before clear: { 1 2 3 }
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Size=3
 +
After clear: { }
 +
Size=0
 +
|forward_list=
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Before clear: { 1 2 3 }
 +
After clear: { }
 +
|map
 +
|multimap
 +
|flat_map
 +
|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
 +
After clear: { }
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Size=0
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}}
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}}
 +
<!---->
 +
{{#switch:{{#var:cont}}|inplace_vector|flat_map|flat_set|flat_multimap|flat_multiset=|
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{cpp/container/if seq|{{#var:cont}}|
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{{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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-->{{cpp/container/if ord|{{#var:cont}}|
 +
{{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()}}'}}
 +
}}<!--
 +
-->{{cpp/container/if unord|{{#var:cont}}|
 +
{{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}}
 +
}}
 +
<!---->
 +
{{dr list end}}
 +
}}
 +
<!---->
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{#ifeq: {{{1|}}} | forward_list
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{{#ifeq:{{#var:cont}}|forward_list
−
| {{dsc inc | cpp/container/dcl list erase_after |{{{1|}}}}}
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|{{dsc inc|cpp/container/dsc erase_after|{{#var:cont}}}}
−
| {{dsc inc | cpp/container/dcl list 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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