unordered_set::insert
Inserts an element or a range of elements into an unordered_set.
pair<iterator,bool> insert(
const value_type& Val
); // single element
iterator insert(
const_iterator Where,
const value_type& Val
); // single element with hint
template<class ValTy>
pair<iterator,bool> insert(
ValTy&& Val
); // single element, perfect forwarded
template<class ValTy>
iterator insert(
const_iterator Where,
ValTy&& Val
); // single element, perfect forwarded, with hint
template<class InputIterator>
void insert(
InputIterator First,
InputIterator Last
); // range
void insert(
initializer_list<value_type> IList
); // initializer list
Parameters
Parameter |
Description |
Val |
The value of an element to be inserted into the unordered_set unless it already contains an element whose key is equivalently ordered. |
Where |
The place to start searching for the correct point of insertion. |
ValTy |
Template parameter that specifies the argument type that the unordered_set can use to construct an element of value_type, and perfect-forwards Val as an argument. |
First |
The position of the first element to be copied. |
Last |
The position just beyond the last element to be copied. |
InputIterator |
Template function argument that meets the requirements of an input iterator that points to elements of a type that can be used to construct value_type objects. |
IList |
The initializer_list from which to copy the elements. |
Return Value
The first and third member functions (single element) return a pair whose bool component is true if an insertion was made, and false if the unordered_set already contained an element whose key had an equivalent value in the ordering. The iterator component of the return-value pair points to the newly inserted element if the bool component is true, or to the existing element if the bool component is false.
The second and fourth member functions (single element with hint) return an iterator that points to the position where the new element was inserted into the unordered_set or, if an element with an equivalent key already exists, to the existing element.
Remarks
No iterators, pointers, or references are invalidated by this function.
During the insertion of just one element, if an exception is thrown but does not occur in the container's hash function, the container's state is not modified. If the exception is thrown in the hash function, the result is undefined. During the insertion of multiple elements, if an exception is thrown, the container is left in an unspecified but valid state.
To access the iterator component of a pairpr that's returned by the first or third member function, use pr.first; to dereference the iterator within the returned pair, use *pr.first, giving you an element. To access the bool component, use pr.second. For an example, see the sample code later in this article.
The value_type of a container is a typedef that belongs to the container, and, for set, unordered_set<V>::value_type is type const V.
The range member function:
template<class InputIterator>
void insert(
InputIterator First,
InputIterator Last
); // range
inserts the sequence of element values into an unordered_set that corresponds to each element addressed by an iterator in the range [First, Last); therefore, Last does not get inserted. The container member function end() refers to the position just after the last element in the container—for example, the statement s.insert(v.begin(), v.end()); attempts to insert all elements of v into s. Only elements that have unique values in the range are inserted; duplicates are ignored. To observe which elements are rejected, use the single-element versions of insert.
The initializer list member function:
void insert(
initializer_list<value_type> IList
); // initializer list
uses an initializer_list to copy elements into the unordered_set.
For insertion of an element constructed in place—that is, no copy or move operations are performed—see set::emplace and set::emplace_hint.
For a code example, see set::insert.
Requirements
Header: <unordered_set>
Namespace: std