THINK++ — Engineering Visualized

Key-Value Pair

STL Map

An associative container that stores elements as a pair of key and value. Each key must be unique, and it acts as an index to its value.

USAGE

#include <map>
map<string, int> ageMap;

ageMap["Alice"] = 25;
ageMap["Bob"] = 30;

cout << ageMap["Alice"]; // 25
cout << ageMap.size();    // 2

ORDERED MAP

Keys are sorted. O(log N) for search/insert. Uses Red-Black Tree.

UNORDERED MAP

Keys are NOT sorted. O(1) average for search/insert. Uses Hashing.

ITERATING OVER MAP

for (auto const& [key, val] : ageMap) {
    cout << key << ":" << val << endl;
}

The above structured binding syntax requires C++17.

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