Final Touches: Multiple-File Programs, Inheritance, Templates

1. Final Touches: Multiple-File Programs, Inheritance, Templates • Multiple-File Programs • header files • implementation files • main-program file) • Inheritance in C++ • Templates in C++ CS 103

2. Why Multiple Files • Re-use • Better data abstraction (data hiding) • More manageability of large programs CS 103

3. The Multiple-File Approach • Have each major class as a separate program • Re-use: The class can then be used by other programs using the #include macro instead of the copy-&-paste approach • Put the class/function declarations in a header (.h) file, and the class/function implementations in another (.c or .cpp) file. This achieves data hiding. CS 103

4. Project1.cpp file: Example Stack.h file: Stack.cpp file: class Stack { public: typedef int dtype; Stack(int cap=100); int getCapacity(); void push(dtype b); dtype pop(); dtype peek(); bool isEmpty(); private: dtype *dataptr; int top; int capacity; }; #include "Stack.h" Stack::Stack(int cap){ top=0; capacity = (cap>0)?cap:100; dataptr = new int[capacity]; }; int Stack::getCapacity( ) { return capacity; }; int Stack::dtype Stack::pop(){ assert(!isEmpty()); return dataptr[--top]; }; // the implementation of // the remaining methods ........ #include <cstdlib> #include <iostream> #include "Stack.h” using namespace std; // local stuff, if any int main(int argc, char *argv[]){ ……… } CS 103

5. What should Go into a .h File • Only declarations (i.e., info to the compiler) • Nothing that requires storage • Reason: • a header file gets included in several files of a project; • if storage for a variable (or for a code) is allocated multiple times, you get a multiple-definition compilation error • Advanced: One exception to this rule is static data (data local to a file), because the linker does not allocate multiple instances to static data. CS 103

6. Redeclarations Issues • An X.h file can have: #include “Y.h” • Consider this scenario: • The X.h file has: #include “Y.h” #include “Z.h” • The Y.h file has: #include “Z.h” • This means: the declarations in Z.h are included twice in X.h. The second declarations are called redeclarations • Class redeclarations are not allowed. • So, we have a problem CS 103

7. Redeclarations Issue Solution • Inside each Z.h file, do: • Add to at the start of the file (right after all the #includes) the next two lines: #ifndef Z_H_ // Not that Z is the name of .h file #define Z_H_ • Add the following line at the very end of Z.h (on a separate line): #enddef CS 103

8. Class Inheritance in C++ • Inheritance allows us to create new classes which are derived from older classes • The derived classes are called subclasses or simply derived classes • The older classes aresuperclasses orparent classesorbase classes • A derived class automatically includes some of its parent's members, and can have additional ones. Notation: base subclass1 subclass2 CS 103

9. Woman Student Lawyer Animal Mother Reptile Person Person Father Grad Man Bird UG Engineer Conceptual Examples of Hierarchical Classes CS 103

10. Syntax for Inheritance • classderivedClass : publicbaseClass { • private : • // Declarations of additional members, if needed. • public: • // Declarations of additional members, if needed. • protected: • // Declarations of additional members, if needed. • } The derived class inherits from the base class: all public members, all protected members (see later), and the default constructor The additional members defined can have the same name (and type) as thoseof the base class (as when some base members are to be redefined) CS 103

11. “Protected” Access • We have seen two access modes in C++ classes: public and private • Public members are directly accessible by users of the class • Private members are NOT directly accessible by users of the class, not even by inheritors • There is a 3rd access mode: protected • Protected members are directly accessible by derived classes but not by other users CS 103

12. Example of Inherited Classes class Shape { protected: int width, height; public: void setDims (int a, int b){ width=a; height=b;} }; class Triangle: public Shape { public: int area ( ) { return (width * height/2); } }; class Rectangle: public Shape { public: int area ( ) { return (width * height); } }; class Square: public Rectangle { public: void setDims (int a){ width=a; height=a;} }; CS 103

13. Another Example of Inherited Classes(A char stack inherited from string) class CharStack: public string{ public: void push(char b){ string str; str += b; insert(0,str);}; char peek( ){return at(0);}; char pop( ){ char a=at(0); erase(0,1); return a; }; // size( ) and empty( ) are the // same in string, so are // inherited as is. } • Observations: • We have no idea how • the string class is • implemented, and we • don’t care • CharStack inherited • from string all the latter’s • public methods, including • size( ) and empty( ) • We implemented push( ), • pop( ) and peek( ) using • the public methods of • the string class CS 103

14. More on Inheritance Syntax classderivedClass : protectedbaseClass { …}; // Effect: all public members inherited from baseClass are // now protected members of derivedClass classderivedClass : privatebaseClass { …}; // Effect: all public and protected members inherited from // baseClass are now private members of derivedClass Multiple inheritance A class can inherit several classes at once: classderivedClass:publicbaseClass1,publicbaseClass2{ …}; Remark: Not recommended CS 103

15. Templates • We saw function templates early on • Templates allow us to turn the type of data into a parameter that can be changed at will • For example, we defined stacks/queues/trees of ints • If we want a stack/queues/trees of floats, we have to cut and paste, and change the data type from int to float • We reduced this effort by using: typedef int datatype; • That is still inconvenient, time-consuming, and error prone • With templates, we do not need to cut+paste+change CS 103

16. Function Templates (Reminder ) template<classtype> function_declaration; -Or- template<typenametype> function_declaration; • Syntax for declaring a function template: Example of a FunctionTemplate Declaration: // Returns the minimum of array x[ ]. The data // type of x[ ] is arbitrary & customizable template<typename T> T min(T x[], int length){ T m = x[0]; // M is the minimum so far for (int i=1;i<n;i++) if (x[i]<m) m=x[i]; return m; } Example of Use: int x[]= {11, 13, 5, 7, 4, 10}; double y[]= {4.5, 7.13, 17}; int minx = min<int>(x,6); double miny= min<double>(y,3); CS 103

17. Templates with More than One Generic Type • Templates can have several generic types • Syntax for their declaration: • class can be replaced by typename. template<classtype1,classtype2> funct_decl; CS 103

18. Class Templates • Much as function templates allow argument types to be parameterized, class templates allow us to parameterize the types of: • member variables • arguments of member functions & constructors • return values of member functions • The syntax is similar but somewhat more cumbersome CS 103

19. Class Templates Syntax • For class template declaration: • For the implementation of the methods outside the class, the syntax is: • For the implementation of the constructors outside the class, the syntax is: template<class T> class_declaration; template<class T> return_type className<T>::methodName(parameter-list){ ……} template<class T> className<T>:: className(parameter-list){……} CS 103

20. Stack as a ClassTemplate template <class T> class stack { private : T *dataptr; int top; int capacity; public: stack(int cap=100); int getCapacity() {return capacity;} void push(T b); T pop() {assert(top>0); return dataptr[--top];} bool isEmpty() {return top==0;} }; CS 103

21. template<class T> stack<T>::stack(int cap){ top=0; capacity = (cap>0)?cap:100; dataptr = new T[capacity]; } template<class T> void stack<T>::push(T b){ if (top < capacity) dataptr[top++]=b; else{ capacity *=2; T *newptr=newT[capacity]; for(int k=0;k<capacity/2;k++) newptr[k]=dataptr[k]; delete [] dataptr; dataptr = newptr;dataptr[top++]=b; } } CS 103

22. A Complete Program Using a Stack Template #include <cstdlib> #include <iostream> usingnamespace std; // template stack definition goes here int main(int argc, char *argv[]){ stack<int> intS(5); // a stack of integers cout<<"intS capacity after construction = "<<intS.getCapacity()<<endl; int x[]={2,3,7,8,-10,14,5}; for (int i=0;i<7;i++) intS.push(x[i]); cout<<"intS capacity after pushing 7 elements="<< intS.getCapacity(); cout<<“\nEmptying intS: "; while (!intS.isEmpty()) cout<<intS.pop()<<"; "; cout<<endl; CS 103

23. stack<char *> stringS(5); // a stack of strings stringS.push("hi"); stringS.push("there"); cout<<"Emptying stringS: "; while (!stringS.isEmpty()) cout<<stringS.pop()<<"; "; cout<<endl; double y[]={3.14,9.8,1.42,12}; stack<double> doubleS(y,4); // a stack of doubles cout<<"doubleS capacity="<<doubleS.getCapacity()<<endl; cout<<"Emptying doubleS: "; while (!doubleS.isEmpty()) cout<<doubleS.pop()<<"; "; cout<<endl; } CS 103

24. C++ Standard Templates Library (STL) • C++ comes with a library that supports most of the data structures (i.e., classes) we covered in this semester CS 103

25. Some Operations of STL Classes CS 103