std::deque: How do I get an iterator pointing to the element at a specified index?

Question

I have a std::deque, and I want to insert an element at a specified index (I'm aware that std::list would be better at this). The deque::insert() function takes an iterator to specify the location to insert. Given an index, how can I get an iterator pointing to that location, so that I can pass that iterator to insert()?

For example:

void insertThing ( deque<Thing> & things, Thing thing, size_t index )
{
   deque<Thing>::iterator it = /* what do I do here? */
   things.insert ( it, thing );
}

I'm sure this is a very basic question, and I apologize for it. It's been a long time since I've used the STL, and I don't see anything in std::deque's member list that obviously does what I want. Thanks.

Answer 1

void insertThing ( deque<Thing> & things, Thing thing, size_t index )
{
   deque<Thing>::iterator it = things.begin() + index;
   things.insert ( it, thing );
}

Answer 2

deque支持随机访问，所以你应该可以说

things.insert( my_deque.begin() + index, thing);

Answer 3

I like clean soulution without warnings in code, so as std::deque::iterator operator+ overloaded for signed integer code like:

void insertThing ( deque<Thing> & things, Thing thing, size_t index )
{
   deque<Thing>::iterator it = things.begin() + index; // warning here
   things.insert ( it, thing );
}

Introduce warning. So better solution I like more:

void insertThing ( deque<Thing> & things, Thing thing, size_t index )
{
   auto it = things.begin();
   std::advance(it, index);     // clean code (warnings from system headers skipped)
   things.insert ( it, thing );
}