is it possible to insert a new element to std::set like in case of std::list for example:
//insert one element named "string" to sublist of mylist
std::list< std::list<string> > mylist;
mylist.push_back(std::list<string>(1, "string"));
Now, mylist has one element of type std::string in its sub-list of type std::list.
How can you do the same in if std::set is the sub-set of std::list my list i.e
std::list<std::set <string>> mylist;
if you can't then why not?
I think this should do the trick:
int main()
{
string s = "test";
set<string> mySet(&s, &s+1);
cout << mySet.size() << " " << *mySet.begin();
return 0;
}
For clarification on the legality and validity of treating &s as an array, see this discussion: string s; &s+1; Legal? UB?
&s+1 yields the next address after s. That would be legal if s were an array, but in this case I think it's undefined behavior. So it only appears to work correctly.std::set<int> foo(&a[0], &a[5]); &a[5] doesn't exist. This usage is common throughout the STL. It is not undefined behavior because the address &a[5] is evaluated (possible because the size of each element is known at compile time), but not dereferenced. I don't see how &a[5] can be legal while at the same time &s+1 is not?&s is akin to a pointer to an array -- an array with 1 element.
std::set doesn't have a constructor that takes an element to be inserted. The best you can do is use the range constructor:
int a[] = {1,2,3,4,5};
std::set<int> foo(a, a+5); // insert the values 1 through 5 into foo
This version takes a begin and end iterator describing the range to be inserted into the set. You can optionally supply a sorting criterion as well. It's not quite what you wanted, but it's close. So if you had your elements stored in a container v, you can insert a new set to your list like this:
list<set<string> > myList;
myList.push_back(set<string>(v.begin(), v.end()));
