Re: About std::list

"Doug Harrison [MVP]" <>
Sat, 28 Jun 2008 17:06:26 -0500
On Sun, 29 Jun 2008 03:06:19 +0700, "Alan Carre" <>

This is something I've always wondered about... which is, yes: "For
std::list, complexity of removing an element is actually O(1)", that is if:

line 1: std::list<T>::iterator itr;
line 2: std::list<T>::erase(itr);

Then the complexity of "line 2" is *certainly* O(1). But what about "itr"?
In order to erase an element (or elements) from a list, I assume we mean to
erase something specific. That is, normally we're going to wind up doing
something like...

MyType SpecificElement(specifics);
std::list<MyType>::iterator itr = MyList.find(SpecificElement);
if(itr != MyList.end()) MyList.erase(itr);

And the complexity becomes ~= O(N) again due to "find".


So my question is this... is there a *safe* way one could store off the
iterator corresponding with a particular object? That way, on destroy one
could write:


Reducing the complexity back to O(1).

The nice thing about list and the associative containers is that erasing
items only invalidates pointers, iterators, and references to the erased
items, and adding items doesn't invalidate anything.

Doug Harrison
Visual C++ MVP

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