Templates templates templates

[JKop]

The following compiles:

#include <iostream>
using std::cout;
using std::endl;

template< class T >
struct DisplayFormat
{
unsigned char radix;
const T* digits;
T decimal_point_symbol;
unsigned char digits_after_decimal_point;
T comma_symbol;
unsigned char digits_until_comma;
};
DisplayFormat<wchar_t> us_display_format =
{ 10 , L"0123456789" , L'.' , 2 , L',' , 3 };
template < DisplayFormat < wchar_t > * df> //THIS LINE
inline void Blah()
{
cout << df->digits << endl;
}

int main()
{
Blah<&us_display_format>();
}

Where I'm having trouble is "THIS LINE". How do I turn:

template < DisplayFormat < wchar_t > * df>

into:
template < template < class T > DisplayFormat < T > * df >
Obviously I've tried the above, but it won't compile.
-JKop

[Alf P. Steinbach]

* JKop:

The following compiles:

#include <iostream>
using std::cout;
using std::endl;

template< class T >
struct DisplayFormat
{
unsigned char radix;
const T* digits;
T decimal_point_symbol;
unsigned char digits_after_decimal_point;
T comma_symbol;
unsigned char digits_until_comma;
};

DisplayFormat<wchar_t> us_display_format =
{ 10 , L"0123456789" , L'.' , 2 , L',' , 3 };

template < DisplayFormat < wchar_t > * df> //THIS LINE
inline void Blah()
{
cout << df->digits << endl;
}

int main()
{
Blah<&us_display_format>();
}

How do I turn:

template < DisplayFormat < wchar_t > * df>

into:

template < template < class T > DisplayFormat < T > * df >

Obviously I've tried the above, but it won't compile.

I don't quite understand what you're asking, but the code doesn't work.

Here's a bit that when substituted in the above code, works:
template< typename CharType >
std::basic_ostream<CharType>& stdOutput();

template<>
std::basic_ostream<char>& stdOutput<char>(){ return std::cout; }

template<>
std::basic_ostream<wchar_t>& stdOutput<wchar_t>(){ return std::wcout; }

template < typename CharType, DisplayFormat<CharType> const * df>
inline void Blah()
{
stdOutput<CharType>() << df->digits << endl;
}
Also the call in 'main' must be adjusted (extra template argument).

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[tom_usenet]

On Tue, 20 Jul 2004 20:42:47 GMT, JKop <NU**@NULL.NULL> wrote:

The following compiles:

#include <iostream>
using std::cout;
using std::endl;

template< class T >
struct DisplayFormat
{
unsigned char radix;
const T* digits;
T decimal_point_symbol;
unsigned char digits_after_decimal_point;
T comma_symbol;
unsigned char digits_until_comma;
};
DisplayFormat<wchar_t> us_display_format =
{ 10 , L"0123456789" , L'.' , 2 , L',' , 3 };
template < DisplayFormat < wchar_t > * df> //THIS LINE
inline void Blah()
{
cout << df->digits << endl;
}

int main()
{
Blah<&us_display_format>();
}

Where I'm having trouble is "THIS LINE". How do I turn:

template < DisplayFormat < wchar_t > * df>

into:
template < template < class T > DisplayFormat < T > * df >

You can do it with two template parameters:

template <class CharT, DisplayFormat<CharT>* df>

and then call it with:

Blah<DisplayFormat<wchar_t>, &us_display_format>();

But why don't you just pass the display format to Blah as a function
parameter rather than a template parameter?

Tom

[JKop]

tom_usenet posted:

You can do it with two template parameters:

template <class CharT, DisplayFormat<CharT>* df>

and then call it with:

Blah<DisplayFormat<wchar_t>, &us_display_format>();

That crossed my mind, but I was hoping I wouldn't have to do that.

But why don't you just pass the display format to Blah as a function
parameter rather than a template parameter?

That was just a contrived example. DisplayFormat<T> is actually going to be
a member of a class.
Thanks for the input,
-JKop