A Complete Guide to Programming in C++ part 61 ppsx

EXERCISE ■ 579 Exercise Modify and complete the definition of the class InhomList, which represents an inhomogeneous list. ■ Write the destructor for the InhomList class.The destructor releases the memory occupied by the remaining list elements. ■ Implement the getPrev() method and both versions of the insert() and insertAfter() methods.The algorithm needed for inserting list ele- ments was described in the section “Implementing an Inhomogeneous List.” ■ Implement the displayAll() method, which walks through the list sequentially, outputting each element. ■ Test insertion and output of list elements. Check whether the comments on the objects are output, if present. ■ Define the getPos() method, which locates the position of an element to be deleted. If the element is in the list, its address is returned. Other- wise a NULL pointer is returned. ■ Write the erasePos() method, which deletes a list element at a given position. Pay attention to whether the element to be deleted is the first or any other element in the list. Since the destructor for Cell was declared virtual, only one version of the deletePos() method is neces- sary. ■ Define the erase() method, which deletes a list element with a given name from the list. ■ Test deletion of list elements. Continually display the remaining elements in the list to be certain. ■ Now implement the copy constructor and assignment. Use the insert() to construct the list, calling the applicable version of the method.You can call the typeid() operator to ascertain the type of the list element currently to be inserted.The operator is declared in the header file typeinfo. Example: if( typeid(*ptr) == typeid(DerivedEl)) The expression is true if ptr references a DerivedEl type object. ■ Then test the copy constructor and the assignment solution 580 ■ CHAPTER 26 ABSTRACT CLASSES ■ SOLUTION // // cell.h // Defines the classes Cell, BaseEl, and DerivedEl. // #ifndef _CELL_ #define _CELL_ #include <string> #include <iostream> using namespace std; class Cell { private: Cell* next; protected: Cell(Cell* suc = NULL ){ next = suc; } public: virtual ~Cell(){ } Cell* getNext() const { return next; } void setNext(Cell* suc) { next = suc; } virtual void display() const = 0; }; class BaseEl : public Cell { private: string name; public: BaseEl( Cell* suc = NULL, const string& s = "") : Cell(suc), name(s){} // Access methods: void setName(const string& s){ name = s; } const string& getName() const { return name; } void display() const { cout << "\n " << "\nName: " << name << endl; } }; SOLUTION ■ 581 class DerivedEl : public BaseEl { private: string rem; public: DerivedEl(Cell* suc = NULL, const string& s="", const string& b="") : BaseEl(suc, s), rem(b){ } // Access methods: void setRem(const string& b){ rem = b; } const string& getRem() const { return rem; } void display() const { BaseEl::display(); cout << "Remark: " << rem << endl; } }; #endif // // List.h : Defines the class InhomList // #ifndef _LIST_H_ #define _LIST_H_ #include "cell.h" class InhomList { private: Cell* first; protected: Cell* getPrev(const string& s); Cell* getPos( const string& s); void insertAfter(const string& s, Cell* prev); void insertAfter(const string& s,const string& b, Cell* prev); void erasePos(Cell* pos); public: InhomList(){ first = NULL; } InhomList(const InhomList& src); ~InhomList(); InhomList& operator=( const InhomList& src); void insert(const string& n); void insert(const string& n, const string& b); void erase(const string& s); void displayAll() const; }; #endif 582 ■ CHAPTER 26 ABSTRACT CLASSES // // List.cpp : The methods of class InhomList // #include "List.h" #include <typeinfo> // Copy constructor: InhomList::InhomList(const InhomList& src) { // Append the elements from src to the empty list. first = NULL; Cell *pEl = src.first; for( ; pEl != NULL; pEl = pEl->getNext() ) if(typeid(*pEl) == typeid(DerivedEl)) insert(dynamic_cast<DerivedEl*>(pEl)->getName(), dynamic_cast<DerivedEl*>(pEl)->getRem()); else insert(dynamic_cast<BaseEl*>(pEl)->getName()); } // Assignment: InhomList& InhomList::operator=(const InhomList& src) { // To free storage for all elements: Cell *pEl = first, *next = NULL; while( pEl != NULL ) { next = pEl->getNext(); delete pEl; pEl = next; } first = NULL; // Empty list // Copy the elements from src to the empty list. pEl = src.first; for( ; pEl != NULL; pEl = pEl->getNext() ) if(typeid(*pEl) == typeid(DerivedEl)) insert(dynamic_cast<DerivedEl*>(pEl)->getName(), dynamic_cast<DerivedEl*>(pEl)->getRem()); else insert(dynamic_cast<BaseEl*>(pEl)->getName()); return *this; } SOLUTION ■ 583 // Destructor: InhomList::~InhomList() { Cell *pEl = first, *next = NULL; while( pEl != NULL ) { next = pEl->getNext(); delete pEl; pEl = next; } } Cell* InhomList::getPrev(const string& n) { Cell *pEl = first, *prev = NULL; while( pEl != NULL ) { if( n > dynamic_cast<BaseEl*>(pEl)->getName() ) { prev = pEl; pEl = pEl->getNext(); } else return prev; } return prev; } Cell* InhomList::getPos( const string& n) { Cell *pEl = first; while( pEl != NULL && (n != dynamic_cast<BaseEl*>(pEl)->getName())) pEl = pEl->getNext(); if( pEl != NULL && n == dynamic_cast<BaseEl*>(pEl)->getName()) return pEl; else return NULL; } void InhomList::insertAfter(const string& s, Cell* prev) { if( prev == NULL ) // Insert at the beginning: first = new BaseEl( first, s); else // In the middle or at the end: { Cell* p = new BaseEl(prev->getNext(), s); prev->setNext(p); } } 584 ■ CHAPTER 26 ABSTRACT CLASSES void InhomList::insertAfter( const string& s, const string& b, Cell* prev) { if( prev == NULL ) // Insert at the beginning: first = new DerivedEl( first, s, b); else // In the middle or at the end: { Cell* p = new DerivedEl(prev->getNext(), s, b); prev->setNext(p); } } void InhomList::insert(const string& n) { Cell* pEl = getPrev(n); insertAfter(n, pEl); } void InhomList::insert(const string& n, const string& b) { Cell* pEl = getPrev(n); insertAfter(n, b, pEl); } void InhomList::erasePos(Cell* pos) { Cell* temp; if( pos != NULL) if( pos == first ) // Delete the first element { temp = first; first = first->getNext(); delete temp; } else // Delete from the middle or at the end { // Get the predecessor temp = getPrev( dynamic_cast<BaseEl*>(pos) ->getName()); if(temp != NULL) // and bend pointer. temp->setNext(pos->getNext()); delete pos; } } void InhomList::erase(const string& n) { erasePos( getPos(n)); } SOLUTION ■ 585 void InhomList::displayAll() const { Cell* pEl = first; while(pEl != NULL) { pEl->display(); pEl = pEl->getNext(); } } // // List_t.cpp : Tests the sorted inhomogeneous list // #include "List.h" int main() { InhomList liste1; cout << "\nTo test inserting. " << endl; liste1.insert("Bully, Max"); liste1.insert("Cheers, Rita", "always merry"); liste1.insert("Quick, John", "topfit"); liste1.insert("Banderas, Antonio"); liste1.displayAll(); cin.get(); cout << "\nTo test deleting. " << endl; liste1.erase("Banderas, Antonio"); liste1.erase("Quick, John"); liste1.erase("Cheers, Rita"); liste1.displayAll(); cin.get(); cout << "\n " << "\nGenerate a copy and insert an element. " << endl; InhomList liste2(liste1), // Copy constructor liste3; // and an empty list. liste2.insert("Chipper, Peter", "in good temper"); liste3 = liste2; // Assignment cout << "\nAfter the assignment: " << endl; liste3.displayAll(); return 0; } This page intentionally left blank 587 Multiple Inheritance This chapter describes how new classes are created by multiple inheritance and explains their uses. Besides introducing you to creating and destroying objects in multiply-derived classes, virtual base classes are depicted to avoid ambiguity in multiple inheritance. chapter 27 588 ■ CHAPTER 27 MULTIPLE INHERITANCE class MotorHome : public Car, public Home { private: // Additional private members here protected: // Additional protected members here public: // Additional public members here }; Car Home MotorHome ■ MULTIPLY-DERIVED CLASSES The multiply-derived class MotorHome Definition scheme for class MotorHome . classes are created by multiple inheritance and explains their uses. Besides introducing you to creating and destroying objects in multiply-derived classes, virtual base classes are depicted to. elements. Continually display the remaining elements in the list to be certain. ■ Now implement the copy constructor and assignment. Use the insert() to construct the list, calling the applicable version. NULL; } InhomList(const InhomList& src); ~InhomList(); InhomList& operator=( const InhomList& src); void insert(const string& n); void insert(const string& n, const string&