| Name | Expression | Precondition | Semantics | Postcondition |
| Default constructor | X() X a; | | Creates an empty container. | The size of the container is 0. |
| Erase key | a.erase(k) | | Destroys all elements whose key is the same as k, and removes them from a. [2] The return value is the number of elements that were erased, i.e. the old value of a.count(k). | a.size() is decremented by a.count(k) . a contains no elements with key k. |
| Erase element | a.erase(p) | p is a dereferenceable iterator in a. | Destroys the element pointed to by p, and removes it from a. | a.size() is decremented by 1. |
| Erase range | a.erase(p, q) | [p, q) is a valid range in a. | Destroys the elements in the range [p,q) and removes them from a. | a.size() is decremented by the distance from i to j. |
| Clear | a.clear() | | Equivalent to a.erase(a.begin(), a.end()) | |
| Find | a.find(k) | | Returns an iterator pointing to an element whose key is the same as k, or a.end() if no such element exists. | Either the return value is a.end(), or else the return value has a key that is the same as k. |
| Count | a.count(k) | | Returns the number of elements in a whose keys are the same as k. | |
| Equal range | a.equal_range(k) | | Returns a pair P such that [P.first, P.second) is a range containing all elements in a whose keys are the same as k. [3] If no elements have the same key as k, the return value is an empty range. | The distance between P.first and P.second is equal to a.count(k) . If p |
