std::map - cppreference.com

std::map is a sorted associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function Compare. Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as red-black trees.

Everywhere the standard library uses the Compare requirements, uniqueness is determined by using the equivalence relation. In imprecise terms, two objects a and b are considered equivalent (not unique) if neither compares less than the other: !comp(a, b) && !comp(b, a).

std::map meets the requirements of Container, AllocatorAwareContainer, AssociativeContainer and ReversibleContainer.

[edit] Member types

[edit] Member classes

[edit] Member functions

[edit] Non-member functions

[edit] Deduction guides (since C++17)

[edit] Example

#include <iostream>
#include <map>
#include <string>
#include <string_view>
 
void print_map(std::string_view comment, const std::map<std::string, int>& m)
{
    std::cout << comment;
    for (const auto& [key, value] : m) {
        std::cout << key << " = " << value << "; ";
    }
    std::cout << "\n";
}
 
int main()
{
    // Create a map of three strings (that map to integers)
    std::map<std::string, int> m { {"CPU", 10}, {"GPU", 15}, {"RAM", 20}, };
 
    print_map("Initial map: ", m);
 
    m["CPU"] = 25;  // update an existing value
    m["SSD"] = 30;  // insert a new value
 
    print_map("Updated map: ", m);
}

Initial map: CPU = 10; GPU = 15; RAM = 20; 
Updated map: CPU = 25; GPU = 15; RAM = 20; SSD = 30;

[edit] Defect reports

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