Re: Two versions of generic functions?

From:
Victor Bazarov <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Tue, 13 Apr 2010 14:10:52 -0400
Message-ID:
<hq2c3u$86e$1@news.datemas.de>
Immortal Nephi wrote:

     I create generic class. Non-unicode string and unicode string
definitions are placed in generic class body. I am unable to place
them into function body. I will have to create two separate
functions. Both functions behave the same.
    First version of function is non-unicode and second version of
function is unicode. Both functions take too much spaces in the
source code. It would be nice to have only one function.
    How do I declare local type variable into function body? Local type
variable will be string and wstring. The C++ Compiler will fail to
compile and error message says redefinition sampleText variables.

template< typename A, typename B, typename C >
class Foo
{
public:
    Foo() {}
    ~Foo() {}

    void Print( A a, B &b, C &c );

    static const A text;
    static const A text2;
};

const std::string Foo< std::string, std::ostream, std::istream >::text
=
    "Non-unicode --> Type your name: ";

const std::wstring Foo< std::wstring, std::wostream, std::wistream

::text =
    
L"Unicode --> Type your name: ";

const std::string Foo< std::string, std::ostream, std::istream

::text2 =
    
"\n\nNon-unicode --> Your name is ";

const std::wstring Foo< std::wstring, std::wostream, std::wistream

::text2 =
    
L"\n\nUnicode --> Your name is ";

template< typename A, typename B, typename C >
void Foo< A, B, C >::Print( A a, B &b, C &c )
{
    A sampleText;
    std::string sampleText = ?Non-unicode string?;
    std::wstring sampleText = L?Unicode string?; // error redefinition

Isn't your 'A' type the type you need to declare 'sampleText'? If so,
use it:

      A sampleText;

Since you want to initialize it here, you need a helper class that would
contain that string in its static member, something like

   template<class ST> struct FooHelper {
       static const ST str;
   };

   std::string const FooHelper<std::string>::str("narrow");
   std::wstring const FooHelper<std::wstring>::str(L"wide");

    ...

   template<typename A ...> void FOO<A,B,C>::Print(...

      A sampleText = FooHelper<A>::str;

     A name;

    b << a << std::endl << text;
    c >> name;

    b << text2 << name << std::endl;
}

int main()
{
    Foo< std::string, std::ostream, std::istream > f;
    f.Print( "Non-unicode String", std::cout, std::cin );

    Foo< std::wstring, std::wostream, std::wistream > f2;
    f2.Print( L"Unicode String", std::wcout, std::wcin );

    return 0;
};


V
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