public member function
<set>
std::multiset::lower_bound
iterator lower_bound (const value_type& val) const;
const_iterator lower_bound (const value_type& val) const;
iterator lower_bound (const value_type& val);
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 multiset 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 multiset contains elements equivalent to val: In this case lower_bound returns an iterator pointing to the first of such elements, whereas upper_bound returns an iterator pointing to the element following the last.
Parameters
- val
- Value to compare.
Member type value_type is the type of the elements in the container, defined in multiset 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 multiset::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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// multiset::lower_bound/upper_bound
#include <iostream>
#include <set>
int main ()
{
std::multiset<int> mymultiset;
std::multiset<int>::iterator itlow,itup;
for (int i=1; i<8; i++) mymultiset.insert(i*10); // 10 20 30 40 50 60 70
itlow = mymultiset.lower_bound (30); // ^
itup = mymultiset.upper_bound (40); // ^
mymultiset.erase(itlow,itup); // 10 20 50 60 70
std::cout << "mymultiset contains:";
for (std::multiset<int>::iterator it=mymultiset.begin(); it!=mymultiset.end(); ++it)
std::cout << ' ' << *it;
std::cout << '\n';
return 0;
}
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Notice that lower_bound(30) returns an iterator to 30, whereas upper_bound(40) returns an iterator to 50.
mymultiset contains: 10 20 50 60 70
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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 multiset is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.