std::set is an associative container that contains a sorted set of unique objects of typeKey. Sorting is done using the key comparison functionCompare. Search, removal, and insertion operations have logarithmic complexity. Sets are usually implemented asRed–black trees.

Everywhere the standard library uses theCompare requirements, uniqueness is determined by using the equivalence relation. In imprecise terms, two objectsa andb are considered equivalent if neither compares less than the other:!comp(a, b)&&!comp(b, a).

std::set meets the requirements ofContainer,AllocatorAwareContainer,AssociativeContainer andReversibleContainer.

[edit]Template parameters

[edit]Member types

[edit]Member functions

[edit]Non-member functions

[edit]Notes

The member typesiterator andconst_iterator may be aliases to the same type. This means defining a pair of function overloads using the two types as parameter types may violate theOne Definition Rule. Sinceiterator is convertible toconst_iterator, a single function with aconst_iterator as parameter type will work instead.

[edit]Example

#include <algorithm>#include <iomanip>#include <iostream>#include <iterator>#include <set>#include <string_view> template<typename T>std::ostream& operator<<(std::ostream& out,const std::set<T>& set){if(set.empty())return out<<"{}";    out<<"{ "<<*set.begin();std::for_each(std::next(set.begin()), set.end(),[&out](const T& element){        out<<", "<< element;});return out<<" }";} int main(){    std::set<int> set{1,5,3};std::cout<< set<<'\n';     set.insert(2);std::cout<< set<<'\n';     set.erase(1);std::cout<< set<<"\n\n";     std::set<int> keys{3,4};for(int key: keys){if(set.contains(key))std::cout<< set<<" does contain "<< key<<'\n';elsestd::cout<< set<<" doesn't contain "<< key<<'\n';}std::cout<<'\n'; std::string_view word="element";    std::set<char> characters(word.begin(), word.end());std::cout<<"There are "<< characters.size()<<" unique characters in "<<std::quoted(word)<<":\n"<< characters<<'\n';}

{ 1, 3, 5 }{ 1, 2, 3, 5 }{ 2, 3, 5 } { 2, 3, 5 } does contain 3{ 2, 3, 5 } doesn't contain 4 There are 5 unique characters in "element":{ e, l, m, n, t }

[edit]Defect reports

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

[edit]See also

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