Template methods, declaration and Implementation in header file, andOverloaded methods.

[anto.anish]

Hi ,

Since, i did not want to write explicit instantiations in Source file
of all template methods for various different datatypes that my client
might use, i choose to write implementation of template methods along
with their declarations in the header file. Well, there are also other
files in the project, which include this header file as well, which
all gets compiled, linked and tested well.

#ifndef __ATT_H__
#define __ATT_H__
namespace TESTSPACE
{

class Att : public Abs
{

public:
template<class T>
unsigned long read(T& start, unsigned long count=0)
{
//Implementation written here
}
unsigned long read(std::back_insert_iterator< vector<std::string> >&
start, unsigned long count=0)
{
//Implementation written here
}


template<class T>
unsigned long write(T& start, T& stop)
{
//Implementation written here
}
unsigned long write(vector <std::string>::iterator& start, vector
<std::string>::iterator& stop)
{
//Implementation written here
}

};
}
#endif




However, to keep the header file look more reader friendly with just
declarations and moving all the implementation towards the end of the
header file as given below, however generates me errors as
"error C2373: 'TESTSPACE::Att::read' : redefinition; different type
modifiers.
What am i missing here ? The template functions are basically
overloaded methods, then why does the compiler throw error for the
below code ?
#ifndef __ATT_H__
#define __ATT_H__
namespace TESTSPACE
{

class Att : public Abs
{

public:
template<class T>
unsigned long read(T& start, unsigned long count=0);
unsigned long read(std::back_insert_iterator< vector<std::string> >&
start, unsigned long count=0);


template<class T>
unsigned long write(T& start, T& stop);
unsigned long write(vector <std::string>::iterator& start, vector
<std::string>::iterator& stop);

};

//All implementations done here temporarily
//Move below code to a separate "impl.h" file later
template<class T>
unsigned long Att::read(T& start, unsigned long count)
{
//Implementation written here
}
unsigned long Att::read(std::back_insert_iterator<
vector<std::string> >& start, unsigned long count)
{
//Implementation written here
}


template<class T>
unsigned long Att::write(T& start, T& stop)
{
//Implementation written here
}
unsigned long Att::write(vector <std::string>::iterator& start,
vector <std::string>::iterator& stop)
{
//Implementation written here
}
}
#endif

 

[metarox]

If you do a template specialization, you have to tell the compiler
that it's one with "template <>" else the compiler will simply tell
you that your second function is already included in the template
declared version which is why you get that message when he reaches the
second read method. Also you can't partially specialize templated
functions, they need to be fully specialized.

You can also specialize the functions outside of the template file.h.

template<class T>
unsigned long Att::read(T& start, unsigned long count)
{
//Implementation written here
}

template<>
unsigned long Att::read(std::back_insert_iterator<
vector<std::string> >& start, unsigned long count)
{
//Implementation written here
}

David