Template print function C++

user_9830735 0
Viewed 3250

so far I wrote this:

template <typename TType>
void print_vector(const std::vector<TType>& vec)
{
    typename  std::vector<TType>::const_iterator it;
    std::cout << "(";
    for(it = vec.begin(); it != vec.end(); it++)
    {
        if(it!= vec.begin()) std::cout << ",";
        std::cout << (*it);
    }
    std::cout << ")";
}

template<>
template <typename T2>
void print_vector(const std::vector< std::vector<T2> >& vec)
{
    for( auto it= vec.begin(); it!= vec.end(); it++)
    {
        print_vector(*it);
    }
}

The first function works fine for things like std::vector< double> and so on. Now I want to be able to print std::vector< std::vector< TType>> things as well. The second part doesn't compile, but that's the "idea" I have of solving my task. Any suggestions on how to achieve that kind of behavior?

Compilation Error: too many template-parameter-lists

templates printing c++
3 Answers

Remove the template<> part, function template overloading would work fine.

template <typename TType>
void print_vector(const std::vector<TType>& vec)
{
    typename  std::vector<TType>::const_iterator it;
    std::cout << "(";
    for(it = vec.begin(); it != vec.end(); it++)
    {
        if(it!= vec.begin()) std::cout << ",";
        std::cout << (*it);
    }
    std::cout << ")";
}

template <typename T2>
void print_vector(const std::vector< std::vector<T2> >& vec)
{
    for( auto it= vec.begin(); it!= vec.end(); it++)
    {
        print_vector(*it);
    }
}
user_33097900

You may actually want to go for a more generic solution to the problem, allowing to print pretty much any iterable type:

#include <vector>
#include <iostream>

template <typename Iterable>
std::ostream& operator<<(std::ostream& os, const Iterable& vals)
{
    for (const auto& val : vals)
        os << val << std::endl;
    return os;
}

int main()
{
    auto simple_vec = std::vector<int>{3, 5 , 7};
    std::cout << simple_vec;
    auto nested_vec = std::vector<std::vector<int>>{{1, 2}, {3, 4}};
    std::cout << nested_vec;
}

For further improvements on this solution, you could try using SFINAE, to make sure the templated << is only available for iterable types.

user_64499490

If you make your function to print base types and override for vector using itself recursively:

template<typename T>
void print( const T &t ) 
{ 
    std::cout << t; 
}

template<typename T>
void print( const std::vector<T> &v ) 
{ 
    std::cout << '[';
    for( auto it = v.begin(); it != v.end(); ++it ) {
         if( it != v.begin() ) std::cout << ',';
         print( *it );
    }
    std::cout << ']';
}

then you do not need to write special one for vector of vectors or vector of vectors of vectors and so on.

live example

user_4323580
Related