public member function
<set>

std::set::lower_bound

iterator lower_bound (const value_type& val) const;
      iterator lower_bound (const value_type& val);
const_iterator lower_bound (const value_type& val) const;
Return iterator to lower bound
Returns an iterator pointing to the first element in the container which is not considered to go before val (i.e., either it is equivalent or goes after).

The function uses its internal comparison object (key_comp) to determine this, returning an iterator to the first element for which key_comp(element,val) would return false.

If the set class is instantiated with the default comparison type (less), the function returns an iterator to the first element that is not less than val.

A similar member function, upper_bound, has the same behavior as lower_bound, except in the case that the set contains an element equivalent to val: In this case lower_bound returns an iterator pointing to that element, whereas upper_bound returns an iterator pointing to the next element.

Parameters

val
Value to compare.
Member type value_type is the type of the elements in the container, defined in set as an alias of its first template parameter (T).

Return value

An iterator to the the first element in the container which is not considered to go before val, or set::end if all elements are considered to go before val.

Member types iterator and const_iterator are bidirectional iterator types pointing to elements.

Example

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// set::lower_bound/upper_bound
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  std::set<int>::iterator itlow,itup;

  for (int i=1; i<10; i++) myset.insert(i*10); // 10 20 30 40 50 60 70 80 90

  itlow=myset.lower_bound (30);                //       ^
  itup=myset.upper_bound (60);                 //                   ^

  myset.erase(itlow,itup);                     // 10 20 70 80 90

  std::cout << "myset contains:";
  for (std::set<int>::iterator it=myset.begin(); it!=myset.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return 0;
}


Notice that lower_bound(30) returns an iterator to 30, whereas upper_bound(60) returns an iterator to 70.
myset contains: 10 20 70 80 90

Complexity

Logarithmic in size.

Iterator validity

No changes.

Data races

The container is accessed (neither the const nor the non-const versions modify the container).
Concurrently accessing the elements of a set is safe.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the container.

See also

  • 9316991614 2018-02-25
  • 191841613 2018-02-25
  • 16411612 2018-02-25
  • 6081981611 2018-02-25
  • 1784561610 2018-02-25
  • 4651609 2018-02-25
  • 9348111608 2018-02-25
  • 2513771607 2018-02-25
  • 6478461606 2018-02-24
  • 4985791605 2018-02-24
  • 5637141604 2018-02-24
  • 282181603 2018-02-24
  • 6217941602 2018-02-24
  • 5076141601 2018-02-24
  • 714281600 2018-02-24
  • 6607141599 2018-02-24
  • 949041598 2018-02-24
  • 6809961597 2018-02-24
  • 671871596 2018-02-24
  • 7107821595 2018-02-24