Iterating over vector of custom object with two conditions - c++

Question

Using C++11, I'd like to iterate over a vector and return a type that indicates that the index was not found.
I am use to the traditional for(;;) loop and specifying the index manually, as my code shows below.
inline std::size_t ItemList::FindItem(Items& Item)
{
for (std::size_t i = 0; i < ItemVector.size(); i++)
{
if (ItemVector[i]->GetId() == Item.GetId() && !ItemVector[i]->GetName().compare(Item.GetName()))
{
return i + 1;
}
}
return 0;
}
I'm also having to increment the index +1 in order to return a value of 0 (to accommodate unsigned size_t) to indicate the calling method that the index was not found (I understand this is asinine). I am assuming it would be more suitable to return something more like std::end()?
Would using a C++11 iterator approach be more efficient? The vector will populate to a large number and the find needs to be quick.

Answer 1

You could use std::find_if and work with iterators:
auto it = std::find_if(ItemVector.begin(), ItemVector.end(),
[&Item](Items *value) {
return value->GetId() == Item.GetId() && !value->GetName().compare(Item.GetName());
}
);
Then you can simply test if it != ItemVector.end() to know if you found something.
There will likely be no (or very small) difference between this and your version in term of speed, but it is a cleaner way to check if something was found or not.

Answer 2

Yes, an iterator would be the way to do this, you're actually writing your own version of find_if You could instead do:
find_if(cbegin(ItemVector), cend(ItemVector), [&](const auto& i){ return i.GetId() == Item.GetId() && i.GetName() != Item.GetName(); })
You can test whether the result of this function was found by testing for equality with cend(ItemVector).
Additionally if you need to find the index of the item you can pass this result after cbegin(ItemVector) to: distance
Live Example

Answer 3

My solution for double search condition that Lambda has multiple parameters in find_if
bool check_second_loop(FullFrame *image_track, guint64 object_id, bool *deletion)
{
auto itr= std::find_if(image_track->track_ids.begin(),
image_track->track_ids.end(),
[object_id](const guint64& a)
{
return a == object_id;
});
if (itr != image_track->track_ids.end())
{
image_track->track_ids.erase(itr);
if(image_track->track_ids.size()==0)
{
*deletion = true;
}
return true;
}
else
return false;
}
bool check_first_loop(guint64 object_id, gint source_id)
{
bool deletion = false;
auto it = find_if(full_frame_list.begin(), full_frame_list.end(),
[object_id, &deletion, source_id](FullFrame &x)
{
return check_second_loop(&x, object_id, &deletion)
&& x.camera_number == source_id;
});
if (it != full_frame_list.end())
{
// Found
return true;
}
else
return false;
}