CODEWITHSUNDEEP
c++algorithmstlsetlower-bound
user3243499
user3243499

Reputation: 3151

How to delete elements in a set from begining till one element before iterator using c++ stl?

I have a set of ints as 

set<int> ds;
ds.insert(2); 
ds.insert(3);
ds.insert(4);
ds.insert(5);
ds.insert(6);
ds.insert(7);
ds.insert(8);

set<int>::iterator it = lower_bound(ds.begin(), ds.end(), 6);

I want to delete 2 till 5.

I am currently trying to do like ds.erase(ds.begin(), --it);

But the code freezes and does not progress further. Also, I would not want to erase anything if there are no elements prior to the iterator location.

How to achieve it using c++ STL?

Upvotes: 0

Views: 129

Answers (2)

Sumit Jha
Sumit Jha

Reputation: 1691

First it is pointing to 6 and --it changes it 5. In std::map.erase(first, last)

Iterators specifying a range within the map container to be removed: [first,last). i.e., the range includes all the elements between first and last, including the element pointed by first but not the one pointed by last.Member types iterator and const_iterator are bidirectional iterator types that point to elements.

So you can simply use it instead --it.

ds.erase(ds.begin(),it);

Upvotes: 1

Vlad from Moscow
Vlad from Moscow

Reputation: 310950

Here you are.

#include <iostream>
#include <set>

int main() 
{
    std::set<int> ds = { 2, 3, 4, 5, 6, 7, 8 };

    ds.erase( ds.begin(), ds.lower_bound( 6 ) );

    for ( int x : ds ) std::cout << x << ' ';
    std::cout << std::endl;

    return 0;
}

The program output is

6 7 8

Or

#include <iostream>
#include <set>
#include <algorithm>

int main() 
{
    std::set<int> ds = { 2, 3, 4, 5, 6, 7, 8 };

    ds.erase( ds.begin(), std::lower_bound( ds.begin(), ds.end(), 6 ) );

    for ( int x : ds ) std::cout << x << ' ';
    std::cout << std::endl;

    return 0;
}

The output is the same as shown above.

Upvotes: 4

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