CODEWITHSUNDEEP
c++stliterator
McK
McK

Reputation: 231

How to receive an iterator of strings on STL algorithm

I need to develop an algorithm for a library that receives a "list of strings".

Of course I want to pass an "abstract" iterator to decouple the internal representation of that list (a vector, a linked list, a map...) to the access to it from my function.

This is my approach:

template <typename ForwardIterator>
void myAlgorithm(ForwardIterator itBegin, ForwardIterator itEnd) {
   for(; itBegin != itEnd ; ++itBegin) {
       // Do something with *itBegin
   }
}

My question is, how can I restrict the type of the container to be string? Or even more, is there some way of accepting both std::strings and char* as elements?

Thanks a lot.

Upvotes: 2

Views: 173

Answers (2)

fredoverflow
fredoverflow

Reputation: 263088

You can use std::enable_if to restrict the possible template arguments:

#include <type_traits>
#include <iterator>

template <typename ForwardIterator>
typename std::enable_if<
    std::is_same<
        typename std::iterator_traits<ForwardIterator>::value_type,
        std::string
    >::value, void
>::type
myAlgorithm(ForwardIterator itBegin, ForwardIterator itEnd) {
   for(; itBegin != itEnd ; ++itBegin) {
       // Do something with *itBegin
   }
}

Although I don't really see the point in this restriction.

Is there some way of accepting both std::strings and char* as elements?

Sure, just replace std::is_same with std::is_convertible.

Upvotes: 3

ildjarn
ildjarn

Reputation: 62975

Use a static assertion along with std::iterator_traits<>:

template<typename ForwardIterator>
void myAlgorithm(ForwardIterator itBegin, ForwardIterator itEnd) {
    typedef typename std::iterator_traits<ForwardIterator>::value_type value_t;
    BOOST_STATIC_ASSERT((
        boost::is_same<value_t, std::string>::value ||
        boost::is_same<value_t, char const*>::value
    ));

    for(; itBegin != itEnd ; ++itBegin) {
        // Do something with *itBegin
    }
}

If you're using a C++0x compiler, you can use static_assert instead of BOOST_STATIC_ASSERT and std::is_same instead of boost::is_same.

Upvotes: 5

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