Hello. I am trying to insert elements into an stl vector and I am trying to do it in such a way that it's permanently sorted. So I figured I could use lower_bound, and insert the element there (I know, some may say that if I need to insert elements in the middle of the array, I should choose lists, but I need random access to elements).

So I said

This compiles fine. But the problem is I can't actually get the position. No matter to whom (an integer, an iterator, etc) I assign the value returned by lower_bound, the compiler throws a very descriptive error (yeah, I love stl errors).

I googled for answers, but it seems, there isn't an awful lot of info on this topic.. Everywhere I turn to, people use some vector<int> to demonstrate the issue.

what exact code is causing the error? what is the error?

int a = lower_bound(v.begin(),v.end(),cl,client_com);

produces

int *a = lower_bound(v.begin(),v.end(),cl,client_com);

produces a similar error..

They are the correct errors are they not? they are telling you that function returns an iterator and you are trying to convert to an int and int*.

[edit]
Understanding template errors is learning from past mistakes, I think it would be beneficial if we just spilt that error down so you can look at it.

to
the following is probably the line that throws some confusion
An iterator is a pointer to an element and you have a structure(vector) of client*, and the container is using the default allocator(probably) for the element type.
gcc doc for lower_bound
hope it helps

Can you use a std::map or std::multimap? Those are both associative, but it might be easier to make the order-determining value the key for each element and let the container automatically sort. Or std::set/std::multiset.
ta0kira

I finally made it work with an iterator. At the same point, for some external reason, I decided I can't automatically sort the vector. Thank you all for your answers.

As taOkira points out there maybe a better structure to use possibly a self balancing tree?
Here is a link that could be useful for future reference.

Did you end up at set?

Thank you very much. I am really interested about changing my vectors to maps or sets.

First I must explain my last post. I have a function which adds elements of type client* to an array-like structure (currently this is a vector, in the next few hours it might very well turn into a map or set).

The thing is that at the time when I am adding the element to the set, I don't have it's id. This id is an integer I have to retrieve from a postgres database, after someone, through the network provides some info (login,password) and I decided I will run the query and fetch the result in another thread, so it won't block the rest of the program.. Only then, in that thread can I set the id of the element.

You may ask why do I have to add the client to the array before running the thread.. As you may have figured, this is a network server and I am polling on some file descriptors so it won't block. When some info comes on one of the descriptors, I have to search through some array, to figure out which client said what. So the client must already be in the list, so I can find him when he provides the user and password and set his id..

Now I am thinking of using a separate array for "temporary" users, who haven't yet authenticated themselves. Do you think this is a good idea?

Hello. I did change stuff in my program, and now it works very nice with maps . The problem was I hadn't really understood much about stl (not that I do now, but at least I know more than before ). Thank you very much.