Re: insert and retreave for std::set()

Kevin McCarty <>
Tue, 9 Oct 2012 11:04:41 -0700 (PDT)

On Oct 9, 10:06 am, Rene Ivon Shamberger <> wrote:

Using std::set::insert(), I have stored some data in the container, now I=

 would like to extract the data into another object.inset() method. The pro=
blem is that std::set() does not have a retreave() function. How do I go ab=
out it?

It's hard to answer your question usefully without knowing more about
why you are using an std::set. For instance, why don't you just
insert the strings directly into "someObject" instead of putting them
in an intermediate std::set? Do you need the automatic sorting and
uniqueness enforcement it provides? If so, then (depending on what
"someObject" is), it might be more efficient to instead sort/uniquify
them with STL algorithms in-place after putting them all into
"someObject". If you don't need the sorting / uniqueness checks,
there is no reason to involve the std::set at all.

void insertData(std::string& data){

void someMethod(){
std::set<std::string> set_obj;
// put a lot of elements in the set container
// now put one element a the time inside this method
while(there is data in set_obj){



If you know about a website that has examples of how to extract one eleme=

nt at the time from a 'std::set' please do let me know.


If I understand correctly, you want a function that returns an element
from the set and also removes it from the set at the same time. I
don't think that std::set has any such member function. I agree that
this is a bit of a lack; it would be nice to have a function

  T && std::set<T>::extract(std::set<T>::iterator);

(and similar such functions for other containers where it makes

Lacking that function, you can simulate a loop over the set contents
that achieves what appears to be your aim with:

  while (! set_obj.empty()) {
    someObject.insertData(* set_obj.begin());

This won't be super-efficient, as a copy of the object will be made.
But, since you don't seem to care about the contents of set_obj after
someObject is filled, you could dispense with the calls to erase() and
just loop through:

  for (set<string>::const_iterator it = set_obj.begin(),
       e = set_obj.end(); it != e; ++it)
    someObject.insertData(* it);

or equivalently, if someObject supports a common STL container

  someObject.assign(set_obj.begin(), set_obj.end());

- Kevin B. McCarty

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