How to write a function that takes an iterator or collection in a generic way?

Question

I've been a Java programmer almost exclusively for the past 8 years or so, and recently I've been playing with C++ again. Here's an issue that I've come up against with regards to iterators in C++ STL and Java.

In Java, you can write a method that takes an iterator like this:

void someMethod(Iterator<String> data) {
    // ...
}

You pass in an Iterator and the method does not need to know what the underlying collection of that iterator is, which is good.

In C++, there is no common base class for iterators (as far as I know). I'd have to write a function like this:

void some_function(std::vector<std::string>::const_iterator data) {
    // ...
}

In other words, some_function knows that the iterator is an iterator over a vector. That's not good, because I want the function to work regardless of what the underlying collection of the iterator is.

How can I do this in C++? If it isn't really possible, then what is the best way to create a function in C++ that takes a collection as a parameter, but that doesn't need to know what the exact kind of collection is?

Addendum

Thanks for the answers. In addition to the answers I found some good information on this in paragraph 7.5 (Iterator Traits) of the book The C++ Standard Library: A Tutorial and Reference (by Nicolai M. Josuttis). Paragraph 7.5.1 explains how to write specialized versions of functions for different iterator categories.

Answer 1

You probably want to consider a function template. Look at how some of std <algorithm> function templates work such as std::for_each.

e.g.

template< class Iterator >
void some_function( Iterator first, Iterator last )
{
    // ...
}

You can then call a function generated from this template with many kinds of iterable ranges.

e.g.

std::vector< double > my_doubles;
// ... populate doubles
some_function( my_doubles.begin(), my_doubles.end() );


std::set< Custom > my_custom_class_set;
// ... populate ...
some_function( my_custom_class_set.begin(), my_custom_class_set.end() );

int raw_array[50];
// ... populate ...
some_function( raw_array, raw_array + 50 );