std::vector<int> vlist;
std::vector<int>::iterator itr;
// Add int elements here
// remove every element == 0
for(itr = vlist.begin(); itr != vlist.end(); itr++)
if((*itr) == 0){
itr--;
vlist.erase(itr + 1);
}
std::vector<T>::erase()
Author
Just a quick question this time, since the erase() method invalidates the iterator passed, is the following safe?
For vector<> that's not OK; all iterators are invalidated. For list<> you only invalidate the item pointed at.
However, most people use the semantic of the post-increment to do the same thing.
The problem with your approach is that it fails when you want to delete the first item (as you try to -- on begin()).
[edited by - hplus0603 on November 27, 2003 11:24:55 PM]
However, most people use the semantic of the post-increment to do the same thing.
std::list<> the_list;while( iter != the_list.end() ) { if( SHOULD_DELETE( *iter ) ) { the_list.erase( iter++ ); } else { ++iter; }} The problem with your approach is that it fails when you want to delete the first item (as you try to -- on begin()).
[edited by - hplus0603 on November 27, 2003 11:24:55 PM]
vector::erase() returns an iterator pointing to the value just passed the value erased, so instead of doing the iterator increment/decrement dance, try something like:
However, worrying about invalidated iterators is generally bad news. Consider using std::remove() or std::remove_if() instead. i.e.:
Fewer worries about invalidated iterators, and more efficient to boot.
edit: !@#$! smilies
[edited by - SiCrane on November 27, 2003 11:04:47 PM]
for(itr = vlist.begin(); itr != vlist.end(); ) { if((*itr) == 0){ itr = vlist.erase(itr); // effectively increments the iterator } else { itr++; }} However, worrying about invalidated iterators is generally bad news. Consider using std::remove() or std::remove_if() instead. i.e.:
vlist.erase(std::remove(vlist.begin(), vlist.end(), 0), vlist.end()); Fewer worries about invalidated iterators, and more efficient to boot.
edit: !@#$! smilies
[edited by - SiCrane on November 27, 2003 11:04:47 PM]
Author
Interesting points, I had tried using the return value of erase() within the loop, but for some strange reason I got a runtime error.
I''ll have to look into it again. And yeah my method is clearly not safe as someone had pointed out with my backtracking method.
And I think your method of using std::remove() looks pretty sweet SiCrane, just might do the trick
Cheers again guys, I''m just one step closer to understanding how to properly use STL.
I''ll have to look into it again. And yeah my method is clearly not safe as someone had pointed out with my backtracking method.
And I think your method of using std::remove() looks pretty sweet SiCrane, just might do the trick
Cheers again guys, I''m just one step closer to understanding how to properly use STL.
This topic is closed to new replies.
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