From cppreference.com
voidclear()noexcept;(since C++11)Erases all elements from the container. After this call,
returns zero.
Invalidates any references, pointers, and iterators referring to contained elements. May also invalidate past-the-end iterators.
Complexity
Linear in the size of the container, i.e., the number of elements.
Example
Run this code
#include<iostream>#include<string_view>#include<unordered_set>voidprint_info(std::string_viewrem,conststd::unordered_set<int>&v){std::cout<<rem<<"{ ";for(constauto&value:v)std::cout<<value<<' ';std::cout<<"}\n";std::cout<<"Size="<<v.size()<<'\n';}intmain(){std::unordered_set<int>container{1,2,3};print_info("Before clear: ",container);container.clear();print_info("After clear: ",container);}Possible output:
Before clear: { 1 2 3 } 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
C++11 for unordered associative containers, unclear if complexity
is linear in the number of elements or buckets clarified that it's linear in the number of elements See also