unordered_set size() function in C++ STL Last Updated : 05 Jun, 2023 Comments Improve Suggest changes Like Article Like Report The unordered_set::size() method is a builtin function in C++ STL which is used to return the number of elements in the unordered_set container. Syntax: unordered_set_name.size() Parameter: It does not accepts any parameter. Return Value: The function returns the number of elements in the container. Below programs illustrate the unordered_set::size() function: Program 1: CPP // C++ program to illustrate the // unordered_set.size() function #include <iostream> #include <unordered_set> using namespace std; int main() { unordered_set<int> arr1 = { 1, 2, 3, 4, 5 }; // prints the size of arr1 cout << "size of arr1:" << arr1.size(); // prints the element cout << "\nThe elements are: "; for (auto it = arr1.begin(); it != arr1.end(); it++) cout << *it << " "; return 0; } Output:size of arr1:5 The elements are: 5 1 2 3 4 Program 2: CPP // C++ program to illustrate the // unordered_set::size() function // when container is empty #include <iostream> #include <unordered_set> using namespace std; int main() { unordered_set<int> arr2 = {}; // prints the size cout << "Size of arr2 : " << arr2.size(); return 0; } Output:Size of arr2 : 0 Time complexity: O(1) Comment More infoAdvertise with us B barykrg Follow Improve Article Tags : Misc C++ CPP-Functions cpp-unordered_set cpp-unordered_set-functions +1 More Practice Tags : CPPMisc Explore C++ Programming Language 5 min read C++ OverviewIntroduction to C++ Programming Language 3 min read Features of C++ 5 min read History of C++ 7 min read Interesting Facts about C++ 2 min read Setting up C++ Development Environment 8 min read Difference between C and C++ 3 min read C++ BasicsUnderstanding First C++ Program 4 min read C++ Basic Syntax 4 min read C++ Comments 3 min read Tokens in C 4 min read C++ Keywords 2 min read Difference between Keyword and Identifier in C 3 min read C++ Variables and ConstantsC++ Variables 4 min read Constants in C 4 min read Scope of Variables in C++ 7 min read Storage Classes in C++ with Examples 6 min read Static Keyword in C++ 5 min read C++ Data Types and LiteralsC++ Data Types 7 min read Literals in C 4 min read Derived Data Types in C++ 4 min read User Defined Data Types in C++ 4 min read Data Type Ranges and Their Macros in C++ 3 min read C++ Type Modifiers 4 min read Type Conversion in C++ 4 min read Casting Operators in C++ 5 min read C++ OperatorsOperators in C++ 9 min read C++ Arithmetic Operators 4 min read Unary Operators in C 5 min read Bitwise Operators in C 6 min read Assignment Operators in C 4 min read C++ sizeof Operator 3 min read Scope Resolution Operator in C++ 4 min read C++ Input/OutputBasic Input / Output in C++ 5 min read cin in C++ 4 min read cout in C++ 2 min read Standard Error Stream Object - cerr in C++ 2 min read Manipulators in C++ 4 min read C++ Control StatementsDecision Making in C (if , if..else, Nested if, if-else-if ) 7 min read C++ if Statement 3 min read C++ if else Statement 3 min read C++ if else if Ladder 3 min read Switch Statement in C++ 5 min read Jump statements in C++ 4 min read C++ Loops 7 min read for Loop in C++ 6 min read Range-Based for Loop in C++ 3 min read C++ While Loop 3 min read C++ do while Loop 4 min read C++ FunctionsFunctions in C++ 8 min read return Statement in C++ 4 min read Parameter Passing Techniques in C 3 min read Difference Between Call by Value and Call by Reference in C 4 min read Default Arguments in C++ 5 min read Inline Functions in C++ 6 min read Lambda Expression in C++ 4 min read C++ Pointers and ReferencesPointers and References in C++ 5 min read C++ Pointers 8 min read Dangling, Void , Null and Wild Pointers in C 6 min read Applications of Pointers in C 4 min read Understanding nullptr in C++ 3 min read References in C++ 5 min read Can References Refer to Invalid Location in C++? 2 min read Pointers vs References in C++ 5 min read Passing By Pointer vs Passing By Reference in C++ 5 min read When do we pass arguments by pointer? 5 min read Like