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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.
Contents |
Linear in the size of the container, i.e., the number of elements.
#include <iostream>#include <string_view>#include <map> void print_info(std::string_view rem,conststd::multimap<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::multimap<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=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 224 | C++98 | the complexity waslog(size())+ N, butN was not defined | corrected to 'linear insize()' |
| erases elements (public member function)[edit] |
