set::insert

Inserts an element or a range of elements into a set.

// (1) single element
pair<iterator, bool> insert(
    const value_type& Val
); 

// (2) single element, perfect forwarded
template<class ValTy>
pair<iterator, bool> insert(
    ValTy&& Val
);

// (3) single element with hint
iterator insert(
    const_iterator Where,
    const value_type& Val
); 

// (4) single element, perfect forwarded, with hint
template<class ValTy>
iterator insert(
    const_iterator Where,
    ValTy&& Val
);

// (5) range 
template<class InputIterator> 
void insert(
    InputIterator First,
    InputIterator Last
); 

// (6) initializer list
void insert(
    initializer_list<value_type> IList
);

Parameters

Return Value

The single-element member functions, (1) and (2), return a pair whose bool component is true if an insertion was made, and false if the set already contained an element of 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 single-element-with-hint member functions, (3) and (4), return an iterator that points to the position where the new element was inserted into the 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, the container's state is not modified. 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 single-element member functions, 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, set<V>::value_type is type const V.

The range member function (5) inserts the sequence of element values into a 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 (6) uses an initializer_list to copy elements into the 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.

Example

// set_insert.cpp
// compile with: /EHsc
#include <set>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

template <typename S> void print(const S& s) {
    cout << s.size() << " elements: ";

    for (const auto& p : s) {
        cout << "(" << p << ") ";
    }

    cout << endl;
}

int main()
{

    // insert single values 
    set<int> s1;
    // call insert(const value_type&) version
    s1.insert({ 1, 10 });
    // call insert(ValTy&&) version 
    s1.insert(20);

    cout << "The original set values of s1 are:" << endl;
    print(s1);

    // intentionally attempt a duplicate, single element
    auto ret = s1.insert(1);
    if (!ret.second){
        auto elem = *ret.first;
        cout << "Insert failed, element with value 1 already exists."
            << endl << "  The existing element is (" << elem << ")"
            << endl;
    }
    else{
        cout << "The modified set values of s1 are:" << endl;
        print(s1);
    }
    cout << endl;

    // single element, with hint
    s1.insert(s1.end(), 30);
    cout << "The modified set values of s1 are:" << endl;
    print(s1);
    cout << endl;


    // The templatized version inserting a jumbled range
    set<int> s2;
    vector<int> v;
    v.push_back(43);
    v.push_back(294);
    v.push_back(41);
    v.push_back(330);
    v.push_back(42);
    v.push_back(45);

    cout << "Inserting the following vector data into s2:" << endl;
    print(v);

    s2.insert(v.begin(), v.end());

    cout << "The modified set values of s2 are:" << endl;
    print(s2);
    cout << endl;

    // The templatized versions move-constructing elements
    set<string>  s3;
    string str1("blue"), str2("green");

    // single element
    s3.insert(move(str1));
    cout << "After the first move insertion, s3 contains:" << endl;
    print(s3);

    // single element with hint
    s3.insert(s3.end(), move(str2));
    cout << "After the second move insertion, s3 contains:" << endl;
    print(s3);
    cout << endl;

    set<int> s4;
    // Insert the elements from an initializer_list
    s4.insert({ 4, 44, 2, 22, 3, 33, 1, 11, 5, 55 });
    cout << "After initializer_list insertion, s4 contains:" << endl;
    print(s4);
    cout << endl;
}

Output

The original set values of s1 are:
3 elements: (1) (10) (20)
Insert failed, element with value 1 already exists.
  The existing element is (1)

The modified set values of s1 are:
4 elements: (1) (10) (20) (30)

Inserting the following vector data into s2:
6 elements: (43) (294) (41) (330) (42) (45)
The modified set values of s2 are:
6 elements: (41) (42) (43) (45) (294) (330)

After the first move insertion, s3 contains:
1 elements: (blue)
After the second move insertion, s3 contains:
2 elements: (blue) (green)

After initializer_list insertion, s4 contains:
10 elements: (1) (2) (3) (4) (5) (11) (22) (33) (44) (55)

Requirements

Header: <set>

Namespace: std

See Also

Reference

<set>

set Class

multiset::insert

Standard Template Library