class template partial specialization c++

Class templates can be partially specialized. You can specify special implementations for particular circumstances, but some template parameters must still be defined by the user. For example, for the following class template

template <typename T1, typename T2> class MyClass { . };

the following partial specializations are possible:

// partial specialization: both template parameters have same type template <typename T> class MyClass<T,T> { . }; // partial specialization: second type is int template <typename T> class MyClass<T,int> { . }; // partial specialization: both template parameters are pointer types template <typename T1, typename T2> class MyClass<T1*,T2*> { . };

The following example shows which template is used by which declaration:

MyClass<int,float> mif; // uses MyClass<T1,T2> MyClass<float,float> mff; // uses MyClass<T,T> MyClass<float,int> mfi; // uses MyClass<T,int> MyClass<int*,float*> mp; // uses MyClass<T1*,T2*>

If more than one partial specialization matches equally well, the declaration is ambiguous:

MyClass<int,int> m; // ERROR: matches MyClass<T,T> // and MyClass<T,int> MyClass<int*,int*> m; // ERROR: matches MyClass<T,T> // and MyClass<T1*,T2*>

To resolve the second ambiguity, you can provide an additional partial specialization for pointers of the same type:

template <typename T> class MyClass<T*,T*> { . };

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See Also:
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• Complete Tutorial of C++ Template's
• Standard Template Library Tutorial
• Inter Process Communication Tutorial
• Advance Programming in C & C++

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