Ex643-warning.cpp

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//      Ex643-warning.cpp
 
//      Sec. 6.4 of lecture
//              Dynamic arrays in structures
 
//      Demonstration of   w r o n g   code
//              wrt. copying a structure with pointers
 
//      g++ -g -std=c++11 -Wall -Wextra -pedantic Ex643-warning.cpp
//  valgrind -v --leak-check=yes --tool=memcheck --undef-value-errors=yes --track-origins=yes --log-file=ex643.addr.out --show-reachable=yes ./a.out
 
#include <iostream>
#include <iomanip>                      // setw
#include <cstring>                      // strcpy, strlen
using namespace std;
 
struct Student2
  {
    long long int matrikel;
              int skz;
              char *pname, *pvorname;   // Pointers in structure
  };
 
int main()
{
 Student2 arni;
 char     tmp[20];                      // temp. input string
 
//      ---------------------------------------------------------------
//              Input pvorname
 
 cout << endl << " Vorname : ";
 
//              setw guarantes that not more than 20 characters are read
//                      see Schader/Kuhlin, p.96
 
 cin  >> setw(sizeof(tmp)) >> tmp;
 
//              Allocate memory for arni.pvorname
 
 arni.pvorname = new char[strlen(tmp)+1];// Don't forget "+1
 strcpy(arni.pvorname,tmp);             // and copy input on it
 
//      ---------------------------------------------------------------
//              Input pname
 
 cout << endl << " Familienname : ";
 cin  >> setw(sizeof(tmp)) >> tmp;
 
//              Allocate memory for arni.pname
 
 arni.pname = new char[strlen(tmp)+1];  // Don't forget "+1"
 strcpy(arni.pname,tmp);                // and copy input on it
 
//      ---------------------------------------------------------------
//              Input skz
 
 cout << endl << " Studentenkennzahl : ";
 cin >> arni.skz;
 
//      ---------------------------------------------------------------
//              Input matrikel
 
 cout << endl << " Matrikelnummer    : ";
 cin >> arni.matrikel;
 
//      ---------------------------------------------------------------
//      rough and  w r o n g  copying
 
 const Student2 robbi = arni;   // copies int, long long int, int*
                // but pvorname, pname point on dynamical data are posessed by arni
 
//      ---------------------------------------------------------------
//                              output robbi
 
 cout << endl << "-------- This output is still correct -----------" << endl;
 cout << robbi.pvorname << " "   << robbi.pname    << ", SKZ: ";
 cout << robbi.skz      << "   " << robbi.matrikel << endl << endl;
 
//      ---------------------------------------------------------------
//              Now, we deallocate dynamical data in arni
 
 delete [] arni.pvorname;
 delete [] arni.pname;
 
//      ---------------------------------------------------------------
//                              output robbi
 
 cout << endl << "-------- Even this output might be correct -----------" << endl;
 cout << robbi.pvorname << " "   << robbi.pname    << ", SKZ: ";
 cout << robbi.skz      << "   " << robbi.matrikel << endl << endl;
 
//      ---------------------------------------------------------------
//                              Let us allocate some tiny dynamical array
 char *tiny;
 tiny = new char [5];
 strcpy(tiny,"tiny");
 
//      ---------------------------------------------------------------
//                              output robbi
//      Suddenly, robbi.pname == "tiny"
 
 cout << endl << "-------- Hey, what happend to my output!! -----------" << endl;
 cout << robbi.pvorname << " "   << robbi.pname    << ", SKZ: ";
 cout << robbi.skz      << "   " << robbi.matrikel << endl << endl;
 
//      ---------------------------------------------------------------
//              Now, we deallocate dynamical data in robbi
 
 delete [] robbi.pvorname;
 delete [] robbi.pname;
 return 0;
}