Question

Today I wrote a small predicate to find matching symbols in a container.

But I’m faced to a problem: I want to use this predicate in a std::find_if call inside a const-method of a class, searching in a container that is a member of this class.

But I just noticed that neither std::find nor std::find_if are able to operate on const_iterators !

I checked on some C++ references and it seems there is no version of std::find or std::find_if that accept/return const_iterators. I just can’t understand why, since from what I’ve seen, there is no way that these algorithms could modify the object referenced by the iterator.

Here is how is documented std::find in the SGI implementation:

Returns the first iterator i in the
range [first, last) such that *i ==
value. Returns last if no such
iterator exists.

Answer 1

std::find and std::find_if can definitely operate on *::const_iterator for a given container. Are you by chance looking at the signatures of those functions, and misunderstanding them?

template <class InputIterator, class Type>
InputIterator find(InputIterator first, InputIterator last, const Type& val);

Note that InputIterator here is just a name of a template type parameter, and any const_iterator will satisfy the requirements for it.

Or, perhaps, you’re confusing const_iterator (i.e. an iterator referencing a const value) with a const iterator (i.e. an iterator which is itself const)?