Basic Operations and Usage of C++ map

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Map is a standard C++ container that provides an excellent one-to-one relationship. Creating a map in some programs can achieve twice the result with half the effort. Here's a summary of some basic, simple, and practical map operations!

Most basic map constructors; map<string, int> mapstring; map<int, string> mapint; map<string, char> mapstring; map<char, string> mapchar; map<char, int> mapchar; map<int, char> mapint;
Adding data to map;

map<int, string> maplive; 1. maplive.insert(pair<int, string>(102, "aclive")); 2. maplive.insert(map<int, string>::value_type(321, "hai")); 3. maplive[112] = "April"; // The simplest and most commonly used insertion method for map! 3. Searching for elements in map:

The find() function returns an iterator pointing to the element with the key value, or an iterator to the end of the map if not found.

map<int, string>::iterator l_it; l_it = maplive.find(112); if (l_it == maplive.end()) cout << "we do not find 112" << endl; else cout << "we find 112" << endl; 4. Deleting elements from map: To delete 112; map<int, string>::iterator l_it; l_it = maplive.find(112); if (l_it == maplive.end()) cout << "we do not find 112" << endl; else maplive.erase(l_it); // delete 112; 5. Usage of swap in map: The swap operation in map does not exchange elements within a single container, but rather swaps two containers. For example: #include #include

using namespace std;

int main() { map<int, int> m1, m2, m3; map<int, int>::iterator m1_Iter;

m1.insert(pair<int, int>(1, 10)); m1.insert(pair<int, int>(2, 20)); m1.insert(pair<int, int>(3, 30)); m2.insert(pair<int, int>(10, 100)); m2.insert(pair<int, int>(20, 200)); m3.insert(pair<int, int>(30, 300));

cout << "The original map m1 is:"; for (m1_Iter = m1.begin(); m1_Iter != m1.end(); m1_Iter++) cout << " " << m1_Iter->second; cout << "." << endl;

// This is the member function version of swap //m2 is said to be the argument map; m1 the target map m1.swap(m2);

cout << "After swapping with m2, map m1 is:"; for (m1_Iter = m1.begin(); m1_Iter != m1.end(); m1_Iter++) cout << " " << m1_Iter->second; cout << "." << endl; cout << "After swapping with m2, map m2 is:"; for (m1_Iter = m2.begin(); m1_Iter != m2.end(); m1_Iter++) cout << " " << m1_Iter->second; cout << "." << endl; // This is the specialized template version of swap swap(m1, m3);

cout << "After swapping with m3, map m1 is:"; for (m1_Iter = m1.begin(); m1_Iter != m1.end(); m1_Iter++) cout << " " << m1_Iter->second; cout << "." << endl; }

Map sorting issues: Elements in a map are automatically sorted in ascending order by key, so the sort function cannot be used directly on a map. For example: #include #include

using namespace std;

int main() { map<int, int> m1; map<int, int>::iterator m1_Iter;

m1.insert(pair<int, int>(1, 20)); m1.insert(pair<int, int>(4, 40)); m1.insert(pair<int, int>(3, 60)); m1.insert(pair<int, int>(2, 50)); m1.insert(pair<int, int>(6, 40)); m1.insert(pair<int, int>(7, 30));

cout << "The original map m1 is:" << endl; for (m1_Iter = m1.begin(); m1_Iter != m1.end(); m1_Iter++) cout << m1_Iter->first << " " << m1_Iter->second << endl; } The original map m1 is: 1 20 2 50 3 60 4 40 6 40 7 30 Press any key to continue . . .

Basic map operation functions: C++ Maps are associative containers that store "key/value" pairs. begin() Returns an iterator to the beginning of the map clear() Deletes all elements count() Returns the number of times a specified element appears empty() Returns true if the map is empty end() Returns an iterator to the end of the map equal_range() Returns a pair of iterators for a specific range of elements erase() Deletes an element find() Finds an element get_allocator() Returns the allocator for the map insert() Inserts elements key_comp() Returns the function that compares element keys lower_bound() Returns an iterator to the first element whose key is not less than the given key max_size() Returns the maximum number of elements that can be held rbegin() Returns a reverse iterator to the end of the map rend() Returns a reverse iterator to the beginning of the map size() Returns the number of elements in the map swap() Swaps two maps upper_bound() Returns an iterator to the first element whose key is greater than the given key value_comp() Returns the function that compares element values