Invalid conversion between the same types

Question

I have a function which converts the elements of a vector to a string separated by comma. I want this function to work for numeric values as int, float or double etc. so I have made the function to receive a vector of templates:

template <typename T>
std::string ConvertToString(std::vector<T> elements)
{
    std::stringstream stream;
    for(int i = 0; i < elements.size()-1; i++)
    {
        stream << elements[i];
        stream << ",";
    }
    stream <<elements[elements.size()-1];
    return stream.str();
}

Then I declare and populate a vector:

std::vector<int> values;
values.push_back(1);
values.push_back(2);
values.push_back(3);

And try to call the function:

std::string convertedString = ConvertToString(values);

Now on the call of the above function line I receive the following error :

error C2664: 'ConvertToString' : cannot convert parameter 1 from 'std::vector<_Ty>' to 'std::vector<_Ty>'

I do not understand why do I get this error since the types mentioned are the same. Can somebody explain me where am I wrong and how could I make the function call work?

Thank you very much!

Edit:

I am using Visual Studio 2012.

My full code is this:

#include<string>
#include<iostream>
#include<sstream>
#include<vector>

std::string ConvertToString(std::vector<std::string> strings);

int __cdecl main(int argc, char **argv) 
{
    std::vector<int> values;
    values.push_back(1);
    values.push_back(2);
    values.push_back(3);
    values.push_back(4);
    values.push_back(5);

    std::string convertedValues = ConvertToString(values); //here the error occurs

    return 0;
}

template <typename T>
std::string ConvertToString(const std::vector<T> elements)
{
    std::stringstream stream;
    for(int i = 0; i < elements.size()-1; i++)
    {
        stream << elements[i];
        stream << ",";
    }
    stream <<elements[elements.size()-1];
    return stream.str();
}

Answer 1

When you write this:

std::string ConvertToString(std::vector<std::string> strings);

...before main , you are declaring a function ConvertToString that takes a std::vector<std::string> and return a std::string , so when you try to call it inside main with a std::vector<int> it obviously does not work.

The compiler does not see the templated version of ConvertToString in main , so it cannot call ConvertToString(std::vector<int>) . Change the first declaration of ConvertToString to:

template <typename T>
std::string ConvertToString(const std::vector<T> elements);

And as already mentioned by other answers, you should pass by const reference rather than by value:

template <typename T>
std::string ConvertToString(std::vector<T> const& elements);

Answer 2

This is valid C++03 so is a compiler bug or, more likely (dare I way), a malformed example. (Consider building an example from int main() and submit to the compiler vendor).

Luckily a workaround is available which will be much better anyway. Write

template <typename T> std::string ConvertToString(const std::vector<T>& elements)

ie pass the parameter by const reference, which will also obviate a deep copy of the vector.