Recall the STRCONV example from Chapter 8. The String class in this example has a flaw: It does not protect itself if its objects are initialized to have too many characters. (The SZ constant has the value 80.) For example, the definition String s = “This string will surely exceed the width of the “ “screen, which is what the SZ constant represents.”; will cause the str array in s to overflow, with unpredictable consequences, such as crashing the system. With String as a base class, derive a class Pstring (for “protected string”) that prevents buffer overflow when too long a string constant is used in a definition. A new constructor in the derived class should copy only SZ–1 characters into str if the string constant is longer, but copy the entire constant if it’s shorter. Write a main() program to test different lengths of strings.

SOLUTION:

#include "stdafx.h"

#include "iostream"

#include "string.h"

using namespace std;

/////////////////////////////////////////////////////////////////////////////////////////

class String

{

            protected:

                        enum { SZ = 80 };

                        char str[SZ];

            public:

                        String( )

                        {

                                    str[0] = '\0';

                         }

                        String( char s[ ] )

                        {

                                     strcpy_s(str, s);

                         }

                        void display( ) const

                        {

             cout << str << endl;

 }

                        operator char*( )

                        {

                                     return str;

                         }

};

class Pstring : public String

{

            private:

                        int len;

                        char ss[SZ];

            public:

                        Pstring( )

                        {

                                    String::String( );

                         }

                        Pstring(char s[ ])

                        {

                                    len = strlen(s);

                                    if(len >= SZ)

                                    {

                                                for(int i = 0; i < SZ-1; i++)

                                                            ss[i] = s[i];

                                                ss[SZ-1] = '\0';

                                                strcpy_s(str, ss);

                                    }

                                    else

                                                strcpy_s(str, s);

                        }

                        void display( ) const

                        {

                                    String::display( );

                        }

};

/////////////////////////////////////////////////////////////////////////////////////////

void main( )

{

            Pstring ps1;

            char xstr[] = "Joyeux Noel! ";

            ps1 = xstr;

            ps1.display( );

            Pstring ps2 = "SZ-1 characters into str if the string constant is longer, but copy the entire"

          " constant if it’s shorter. Write a main() program to test different lengths of strings.";

            cout << static_cast<char*>(ps2);

            cout << endl;

            system("pause");

}

OUTPUT:

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