Specification and Implementation Separating the specification from implementation makes it easier to modify programs. Changes in the class’s implementation should not affect the client (as long as the class’s interface has not been changed). Follow these two principles: –Place the class declaration in a header file to be included by any client that wants to use the class (e.g., StackType.h). –Place the definition of the class member functions in a source file (e.g., StackType.cpp)

Multiple definitions When splitting a program into multiple files, the header file needs to be included in each file in which the class is used. To avoid multiple definitions of a class (or even functions), the class specification need to be enclosed in the following preprocessor code: #ifndef NAME #define NAME #endif

Multiple definitions (cont’d) #ifndef STACKTYPE_H #define STACKTYPE_H template class StackType { public: …….. void Push(ItemType); void Pop(ItemType&); private: int top; ItemType *items; }; #endif

Rules when using templates When working with templates, we change the ground rules regarding which file(s) we put the source code into. Previously (i.e., no templates) StackType.cpp could be compiled into object code independently of any client code. Using templates, the compiler cannot instantiate a function template unless it knows the argument to the template This information is found in the client code !!

Rules using templates (cont’d) Two possible solutions –Place the class definition and member function definitions into the same file (e.g., StatckType.h) –Or, give the include directive for the implementation file at the end of the header file

Rules when using templates (cont’d) template class StackType { public: …….. void Push(ItemType); void Pop(ItemType&); private: int top; ItemType *items; }; #include StatckType.cpp