feeding a stringstream to a class member function - c++11

Question

I am a newbie trying to learn by doing. I want to feed a stringstream into a class member function called "print()" but I get errors. Once this works, I can proceed to write more class member functions that work with the data I feed them.
For now I have created a class that has a member function 'print'.
class Month
{
public:
string m_month;
void print()
{
cout << m_month << endl;
}
};
Next, I initialized 12 months:
Month month1 = { "January" };
Month month2 = { "February" };
Month month3 = { "March" };
etc.
When I call "month1.print();" it prints January which is correct.
I used stringstream and a for loop to concatenate month + 1 to 12 and I want to feed the stringstream to the print function.
stringstream os;
string mValue = "month";
int iValue = 1;
for(int i = 0; i < 12; ++i)
{
os << mValue << "" << iValue << "\n";
iValue += 1;
}
However, the stringstream can't be combined with the print function.
os.print(); and os.str().print();
result in "error: ‘std::stringstream {aka class std::__cxx11::basic_stringstream}’ has no member named ‘print’"
Converting the stringstream to char and then feeding it into the print function results in "error: request for member ‘print’ in ‘cstr’, which is of non-class type ‘const char*’"
const string tmp = os.str();
const char* cstr = tmp.c_str();
cstr.print();
Long story short: What I am trying to do is concatenate month + 1 to 12 and feed that to the class member function "print". This seems trivial but I can't get it to work. Any suggestions?
Edit: Full code:
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
class Month
{
public:
string m_month;
void print()
{
cout << m_month << endl;
}
};
int main()
{
Month month1 = { "January" };
Month month2 = { "February" };
Month month3 = { "March" };
Month month4 = { "April" };
Month month5 = { "May" };
Month month6 = { "June" };
Month month7 = { "July" };
Month month8 = { "August" };
Month month9 = { "September" };
Month month10 = { "October" };
Month month11 = { "November" };
Month month12 = { "December" };
stringstream os; // Initialize stringstream "os"
string mValue = "month"; // Initialize mValue "month"
int iValue = 1; // Initialize iValue "1"
for(int i = 0; i < 12; ++i)
{
os << mValue << "" << iValue << "\n"; // Glue mValue and iValue
// together
iValue += 1; // Increment iValue by one
}
send stringstream "os" to the print function // mock code: Here I want to send month1.print(); month2.print(); etc. to the print function. The output should be January, February etc.
return 0;
}

Answer 1

This doesn't do what you think it does:
for(int i = 0; i < 12; ++i)
{
// iValue is actually unnecessary. You could have just used (i + 1)
os << mValue << "" << iValue << "\n";
iValue += 1;
}
All this does is fill the stringstream with the string:
"month1\nmonth2\nmonth3\nmonth4\nmonth5\nmonth6\nmonth7\nmonth8\nmonth9\nmonth10\nmonth11\nmonth12"
Your intent seemed to be to concat a number to the end of a "month" string, and have them act as the month1, month2... variables that you defined above. That's not how it works. You can't (and shouldn't) try to "dynamically" reference variables like that. In os.print();, the stringstream doesn't act as Month simply because it contains a string with the same name as a Month variable.
Instead, add the variables to some kind of container (like a std::vector), and loop over it:
std::vector<Month> months{ month1, month2, month3, ..., month12 }
for (unsigned int i = 0; i < months.size(); i++)
{
months[i].print();
}

Answer 2

A stringstream should be thought of as a stream like any other, except that it happens to be text and held in memory. So it's cheap to convert it to a string, and in fact they are often used for building strings.
But a "Print" method of a class has no business knowing that a stream is a stringstream. All it should care is that it gets a stream which is text, and is input. In fact the former is a bit hard to enforce due to historical weaknesses stretching back a long way. If you just read the stream byte by byte, pass to std::cout, and terminate on EOF then that's probably OK.