Template Question

[Lost User]

Hi everybody. I have the following question. Is it possible to get behavour like this from templates. template < typename T > class TType { public: CString GetAsString( ) { CString sValue; sValue.Format( GetFormat( ), m_tValue ); return sValue; } protected: T m_tValue; }; Define some function that depended of the type will return different string for formating. template < class int > CString GetFormat( ) { return "%d"; } template < class float > CString GetFormat( ) { return "%.4f"; } and then when this is used TType< int > a; // will use template function for int TType< float > a; // will use template function for float

[Martin Vladic]

It is invalid C++. Your idea written correctly looks like this: template class TType { public: CString GetAsString() { CString sValue; sValue.Format(GetFormat(), m_tValue); return sValue; } protected: T m_tValue; }; template CString GetFormat(); template <> CString GetFormat() { return "%d"; } template <> CString GetFormat() { return "%.4f"; } Unfortunately, this doesn't work on VC++ 6.0 (GetFormat is called even for float's). Try this: template class TType { public: TType(const T& value) : m_tValue(value) { } CString GetAsString() { CString sValue; sValue.Format(TypeHelper::GetFormat(), m_tValue); return sValue; } protected: T m_tValue; }; template class TypeHelper; template <> class TypeHelper { public: static CString GetFormat() { return "%d"; } }; template <> class TypeHelper { public: static CString GetFormat() { return "%.4f"; } }; -- Martin

[Lost User]

Are you sure that this will work ?

[Tomasz Sowinski]

You need to create a GetFormat function template and specializations for different types. VC++ seems to have problems with some forms of specializations. I was able to make the following code work:

// in TType template
CString GetAsString()
{
CString sValue;
sValue.Format( GetFormat(m_tValue), m_tValue );
return sValue;
}

// without this specializations won't compile on VC 6
template < class T >
CString GetFormat(const T& unused)
{
return CString();
}

template < >
CString GetFormat(const float & unused)
{
return "%.4e";
}

template < >
CString GetFormat(const int & unused)
{
return "%d";
}

Tomasz Sowinski -- http://www.shooltz.com.pl

[Martin Vladic]

Hm, it seems that discussion boards software stripped some chars from my post. For example, in template specialization definition: template <> class TypeHelper , it stripped "" after class name. Please send me request email, and I will send you correct version of my post. Regards -- Martin

[Martin Vladic]

I found out why some chars was stripped from my message and how to send it correctly. So, here it is, again: It is invalid C++. Your idea written correctly looks like this: template class TType { public: CString GetAsString() { CString sValue; sValue.Format(GetFormat(), m_tValue); return sValue; } protected: T m_tValue; }; template <class T> CString GetFormat(); template <> CString GetFormat<int>() { return "%d"; } template <> CString GetFormat<float>() { return "%.4f"; } Unfortunately, this doesn't work on VC++ 6.0 (GetFormat<int> is called even for float's). Try this: template <class T> class TType { public: TType(const T& value) : m_tValue(value) { } CString GetAsString() { CString sValue; sValue.Format(TypeHelper::GetFormat(), m_tValue); return sValue; } protected: T m_tValue; }; template <class T> class TypeHelper; template <> class TypeHelper<int> { public: static CString GetFormat() { return "%d"; } }; template <> class TypeHelper<float> { public: static CString GetFormat() { return "%.4f"; } }; -- Martin