std::map<Key,T,Compare,Allocator>::clear

 

C++

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Containers library

node-handle (C++17)

Sequence

array (C++11)

vector

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list

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std::map

Member functions

map::map map::~map               map::operator= map::get_allocator

Element access map::at map::operator[] Iterators map::beginmap::cbegin (C++11) map::endmap::cend (C++11) map::rbeginmap::crbegin (C++11)      map::rendmap::crend (C++11) Capacity map::size map::max_size map::empty Observers map::key_comp map::value_comp Modifiers map::clear map::insert map::erase map::swap map::extract (C++17) map::merge (C++17) map::insert_range (C++23) map::insert_or_assign (C++17) map::emplace (C++11) map::emplace_hint (C++11) map::try_emplace (C++17) Lookup map::count map::find map::contains (C++20) map::equal_range map::lower_bound map::upper_bound

Non-member functions

operator==operator<=> (C++20) std::swap(std::map) erase_if(std::map) (C++20)   operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)

Deduction guides(C++17)

 

void clear();		(noexcept since C++11) (constexpr 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 iterator remains valid.

Complexity

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

Example

Run this code

#include <iostream>#include <string_view>#include <map>   void print_info(std::string_view rem, conststd::map<int, char>& v){std::cout<< rem <<"{ ";for(constauto&[key, value]: v)std::cout<<'['<< key <<"]:"<< value <<' ';std::cout<<"}\n";std::cout<<"Size="<< v.size()<<'\n';}   int main(){std::map<int, char> container{{1, 'x'}, {2, 'y'}, {3, 'z'}}; print_info("Before clear: ", container); container.clear(); print_info("After clear: ", container);}

Output:

Before clear: { [1]:x [2]:y [3]:z } Size=3 After clear: { } Size=0

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 224	C++98	the complexity was log(size())+ N, but N was not defined	corrected to 'linear in size()'

See also

erase

erases elements (public member function)