C++: What is the difference between std::map and std::set?

map — key-value pairs. set — keys only.

std::map:

• Key-value pairs.
• Sorted by key.
• O(log n) operations.

1std::map<int, std::string> m;
2m[1] = "one";
3m[2] = "two";

std::set:

• Keys only (no values).
• Sorted.
• O(log n) operations.

1std::set<int> s;
2s.insert(1);
3s.insert(2);

Key difference:

• map — stores key-value pairs.
• set — stores keys only.