Passing a class object into a template function. C++ - c++

Question

I have a template function defined as follows:
template<class T>
string toString(T value) {
ostringstream ss;
if (is_same<T, Student>::value) {
ss << value.getFirst() << ":" << value.getLast() << ":" << value.getId() << ":" << value.getGpa();
return ss.str();
}
else {
//ss << value;
return ss.str();
}
}
If i were to call this function like so:
int main(){
Student studentObj;
toString(studentObj);
}
How do i access this classes various members from the toString function?
I have tried (errors commented)
value.getId() //Returns int
//Error C2228 left of '.getId' must have class/struct/union
and
value<Student>.getId()
//Error C2275 'Student': illegal use of this type as an expression
Thanks in advance!
edit: Class definition
class Student {
protected:
std::string firstname;
std::string lastname;
int id;
float gpa;
public:
Student();
Student(std::string, std::string, int, float);
Student(const Student &);
std::string getFirst();
std::string getLast();
int getId();
float getGpa();
};

Answer 1

No. You cannot do that. With second phase of template code compilation for any non-Student type the if part will fail to compile. Not that if is runtime, not compile time, even though std::is_same is compile time. When you call it as toString(10) the compiler still has to compile it fully for int. It won't evaluate runtime if statement and eliminate the if (true) block - compiler still has to compile it, and produce object code for it. And hence the error.
You just need to specialize it:
template<class T>
string toString(T value)
{
ostringstream ss;
/// skipped code
return ss.str();
}
// SPECIALIZE for 'Student'
template<>
std::string toString(Student s)
{
// Code here
}
Add const and/or & if you want to.

Answer 2

To access the member functions of a class through template function, try calling this way.
Student studentobj;
std::string temp = toString<Student>(studentobj); // This will invoke the member functions of student class
// Code snippet similar to your query
class test
{
public:
test(){}
void callme()
{
std::cout<<"In callme function"<<std::endl;
}
};
template<class T>
void sample(T obj)
{
std::cout<<"In sample function"<<std::endl;
obj.callme();
}
int _tmain(int argc, _TCHAR* argv[])
{
test obj;
sample<test>(obj);
return 0;
}
Output:
In sample function
In callme function