Re: question to understand templates

On 14 Apr., 18:43, Bharath <tiromarc...@[EMAIL PROTECTED]
> wrote:
> Dear all,
> I'm trying learn templates concept.
>
> Here is a line of code from Bjarne Strustrup's C++ programming
> language 3rd edition:
>
> template<class C> struct String<C>::Srep
>
> I couldn't understand what the above line of code means. I'm expecting
> "struct/class <name>" after template<class C>. What exactly
> String<C>::Srep mean? Does "String" refer to STL's string template?

It cannot be the standard library's string class, because
this is located in namespace std (and thus would require
a leading std:: qualifier) and the full class template name
would be std::basic_string. std::basic_string still depends on
it's template parameters charT, traits, and allocator and
a typedef exists for charT = char and all remaining parameters
using some default types as std::string;

Without any further knowledge we can say that above
declaration specifies a class template String, which
depends on some type-parameter C. We can deduce this from
the combination of template<class C> with the name String.
The struct keyword before String<C>::Srep means that
we want to declare an *inner* class struct named Srep
inside the class template String. As written this
declaration is invalid. We can either declare Srep as
part of the class template definition String like this:

template<class C>
struct String { // Defines outer class (template) String
   struct Srep;  // Declares inner class Srep
};

or we can *define* String<C>::Srep out-of-class like
this:

template<class C>
struct String<C>::Srep {
   //...
};

Alternatively, we can also provide the definition of
Srep immediately at the point of it's declaration in
the hosting class template like this:

template<class C>
struct String { // Defines outer class (template) String
   struct Srep { // Defines inner class Srep;
     //...
   };
};

Without using templates you can compare your original
declaration with something like this:

struct StringType { // Defines outer class String
   struct Srep; // Declares inner class Srep
};

// Defines inner class Srep outside of the class StringType:
struct StringType::Srep {
};

HTH & Greetings from Bremen,

Daniel Krügler


-- 
      [ See http://www.gotw.ca/resources/clcm.htm
for info about ]
      [ comp.lang.c++.moderated.    First time posters: Do this! ]