CODEWITHSUNDEEP
c++templates
Neo
Neo

Reputation: 1269

C++ function for container

I want to write a C++ function like:

template <T<int> >
void printIntegers(T<int> ints) {
    for (int i: ints) printf("%d ", i);
}

Because I want T<int> to be either vector<int> or list<int> or any other STL container. How should I write the template parameter?

Upvotes: 0

Views: 235

Answers (3)

N. Shead
N. Shead

Reputation: 3938

You could take a template template parameter as the argument:

template <template <typename...> typename Container>
void printIntegers(Container<int> ints) {
  for (int i : ints) std::printf("%d ", i);
}

See https://en.cppreference.com/w/cpp/language/template_parameters#Template_template_parameter

As other answers have already suggested, though, taking by const reference may be preferable, and there are probably betters ways of doing your example anyway.

Upvotes: 4

Klaus
Klaus

Reputation: 25593

You simply use a template template parameter ( template template parameter subsection there ) like this:

template < template < typename > typename T > void printIntegers( T<int>& container ) 
{
    for ( int el: container ) { std::cout << el << " " ; } 
    std::cout << std::endl;
}


int main()
{
    std::vector<int> i{1,2,3,4};
    std::list<int> l{7,8,9,10};

    printIntegers( i );
    printIntegers( l );
}

Some hints: In your code you did a copy instead of a reference by passing the container into your function. That will generate a lot of overhead by copying the content. The compiler may optimze it out, but you should write it with a reference to get a guarantee to not waste your memory with a copy.

Upvotes: 3

Asteroids With Wings
Asteroids With Wings

Reputation: 17454

Don't overthink it.

template <typename Container>
void printIntegers(const Container& container)
{
    static_assert(std::is_same_v<typename Container::value_type, int>);
    
    for (const auto& el : container)
    {
       printf("%d ", el);
    }
}

Or even just:

template <typename Container>
void printThings(const Container& container)
{
    for (const auto& el : container)
    {
       std::cout << el << ' ';
    }
}

Upvotes: 4

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