unordered_multimap insert() in C++ STL Last Updated : 29 Jul, 2021 Comments Improve Suggest changes Like Article Like Report The function std::unordered_multimap::insert() is a built-in function in C++ STL that extends container by inserting new element in unordered_multimap. This function increases container size by one. The insert() function can be used to insert a single key-value pair, a complete unordered_map, initialized list insertion etc. Syntax: iterator insert(const_iterator position, const value_type& val); Parameters: This method takes following parameters: Position: position to insert elementValue: value to be inserted Return Value: This method returns an iterator pointing to the newly inserted element.Time Complexity: O(1) in average caseO(n) in worst case Below programs illustrate the unordered_multimap::insert function:Program 1: CPP #include <iostream> #include <unordered_map> using namespace std; int main(void) { // Declare unordered_multimap unordered_multimap<char, int> cmap = { { 'B', 2 }, { 'C', 3 }, { 'D', 4 }, { 'E', 5 }, }; // insert a key-value pair using insert() auto pos = cmap.insert(cmap.begin(), pair<char, int>('A', 1)); // print the map with the newly inserted key-value pair for (auto x : cmap) cout << x.first << ": " << x.second << endl; return 0; } Output: A: 1 B: 2 C: 3 D: 4 E: 5 Program 2: CPP #include <iostream> #include <unordered_map> using namespace std; int main() { // Declare unordered_multimap unordered_multimap<char, int> cmap = { { 'b', 2 }, { 'c', 3 }, { 'd', 4 }, { 'e', 5 }, }; unordered_multimap<char, int> dmap = { { 'A', 1 }, { 'G', 6 } }; // Insert the map from begin to end cmap.insert(dmap.begin(), dmap.end()); // Print the map for (auto x : cmap) cout << x.first << ": " << x.second << endl; return 0; } Output: G: 6 A: 1 b: 2 c: 3 d: 4 e: 5 Program 3: CPP #include <iostream> #include <unordered_map> using namespace std; int main() { // Declare unordered_multimap unordered_multimap<char, int> cmap = { { 'B', 2 }, { 'C', 3 }, { 'D', 4 }, { 'E', 5 }, }; // Insert a new list cmap.insert({ { 'A', 1 }, { 'F', 6 }, { 'G', 7 } }); // Print the map for (auto x : cmap) cout << x.first << ": " << x.second << endl; return 0; } Output: G: 7 F: 6 A: 1 B: 2 C: 3 D: 4 E: 5 Comment More infoAdvertise with us Next Article unordered_multimap emplace() function in C++ STL C Chaitanya Tyagi Follow Improve Article Tags : Technical Scripter C++ Technical Scripter 2018 Practice Tags : CPP Similar Reads Unordered Multimap in C++ STL In C++, the unordered_multimap is an unordered associative container that stores data in the form of key-value pairs. It is similar to unordered map, but it allows multiple elements with the same key. It provides fast insertion, deletion and search operations in O(1) time by using hashing.Example:C+ 7 min read unordered_multimap begin() and end() function in C++ STL The unordered_multimap::begin() is a built-in function in C++ STL that returns an iterator pointing to the first element in the container or to the first element in one of its buckets. Syntax: unordered_multimap_name.begin(n) Parameters: The function accepts one parameter. If a parameter is passed, 5 min read unordered_multimap size() function in C++ STL The unordered_multimap::size() is a built-in function in C++ STL which returns the size of the unordered_multimap. It denotes the number of elements in that container. Syntax: unordered_multimap_name.size() Parameters: The function does not accept any parameters. 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