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| Unordered associative | ||||
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| Iterator invalidation | ||||
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| 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.May also invalidate past-the-end iterators.
Contents |
Linear in the size of the container, i.e., the number of elements.
#include <iostream>#include <string_view>#include <unordered_map> void print_info(std::string_view rem,conststd::unordered_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::unordered_map<int,char> container{{1,'x'},{2,'y'},{3,'z'}}; print_info("Before clear: ", container); container.clear(); print_info("After clear: ", container);}
Possible output:
Before clear: { [1]:x [2]:y [3]:z }Size=3After clear: { }Size=0The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2550 | 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 |
| erases elements (public member function)[edit] |
