CODEWITHSUNDEEP
c++templates
lucacerone
lucacerone

Reputation: 10149

How create template functions where both the container and the type are parameters?

This might be a trivial question but is driving me crazy. I want to define a single function foo() that would work with different containers like: vector<int>, vector<double>, set<int> and set<double>.

I have tried to define foo like this:

template<typename CONT, typename T>
   int foo(CONT<T>){
      //evaluate x
      return (int) x ;
   }

This kind of definition doesn't work, but I can't understand why.

How can I achieve something similar?

Upvotes: 0

Views: 88

Answers (2)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 154045

The way to specify both the container class template and its instantiation is to use template template parameters:

template <template <typename...> class Cont, typename T>
int foo(Cont<T>) {
    ...
}

Note that Cont is using a variable number of arguments because otherwise it wouldn't cover the unknown number of defaulted template arguments the standard containers have.

Upvotes: 7

BigBoss
BigBoss

Reputation: 6914

Consider this:

template< class ContainerT >
int foo( ContainerT const& c ) {
}

Then ContainerT can be any thing, including std::vector<int>, std::vector<std::string> or even std::map<std::string, int>. So you don't need to add a new template parameter and if you need to know the type just use value_type of your container:

typedef typename ContainerT::value_type container_type; // Or T in your foo

Upvotes: 5

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