Question

1. Please answer a-d, there was a previous post with additional questions. Thank you in advance.

Consider the following program and provide code and explanations where asked in the code comment after running the program in your system. Note that there are 4 parts (in bold) that need to be addressed.

#include <iostream>

#include <string.h>

using namespace std;

class Header{

private:

    char used;

    int payloadsize;

    char* data;

public:

    Header (){

        used = 0, payloadsize = -1, data = NULL;

    }

    Header (int ps, char initvalue = 0){

        used = 0;

        payloadsize = ps;

        data = new char [payloadsize];

        memset (data, initvalue, payloadsize);

    }

    int getsummation (){

        int sum = 0;

        for (int i=0; i<payloadsize; i++){

            sum += data [i];

        }

        return sum;

    }

};

int main (){

    Header h1;

    Header h2 (10);

    Header* h3 = new Header (20);

    cout << "Header type size " << sizeof (Header) << endl;

    cout << "Header oject size " << sizeof (h1) << endl;      

    cout << "Header object h2 size "<< sizeof (h2) << endl;

    cout << "Header object pointer size " << sizeof (h3) << endl;

    // a. now allocate memory big enough to hold 10 instances of Header

    // b. Put 10 instances of Header in the allocated memory block, one after another without overwriting

            // The instances should have payload size 10, 20,..., 100 respectively

            // and they should have initial values 1,2,...10 respectively

    // c. now call getsummation() on each instance using a loop, output should be:

            // 10, 40, 90, ...., 1000 respectively

    Header* ptr = h3 + 100;

    cout <<"Printing pointer h3: " << h3 << endl;

    cout <<"Printing pointer ptr: " << ptr << endl;

    

    // d. explain the output you see in the following

    cout << "Difference " << (ptr - h3) << " objects" << endl;

    cout << "Difference " << ((char*) ptr - (char *)h3) << " bytes" << endl;

    

}

Answer 1

#include <iostream>

#include <string.h>

using namespace std;

class Header{

private:

char used;

int payloadsize;

char* data;

public:

Header (){

used = 0, payloadsize = -1, data = NULL;

}

Header (int ps, char initvalue = 0){

used = 0;

payloadsize = ps;

data = new char [payloadsize];

memset (data, initvalue, payloadsize);

}

int getsummation (){

int sum = 0;

for (int i=0; i<payloadsize; i++){

sum += data [i];

}

return sum;

}

};

int main (){

Header h1;

Header h2 (10);

Header* h3 = new Header (20);

cout << "Header type size " << sizeof (Header) << endl;

cout << "Header oject size " << sizeof (h1) << endl;

cout << "Header object h2 size "<< sizeof (h2) << endl;

cout << "Header object pointer size " << sizeof (h3) << endl;

// a. now allocate memory big enough to hold 10 instances of Header
Header* H[10];

// b. Put 10 instances of Header in the allocated memory block, one after another without overwriting
for(int i=0;i<10;i++)
{
   H[i]=new Header(10*(i+1),i+1);
   }

// The instances should have payload size 10, 20,..., 100 respectively

// and they should have initial values 1,2,...10 respectively

// c. now call getsummation() on each instance using a loop, output should be:
cout<<endl;
for(int i=0;i<10;i++)
{
   cout<<H[i]->getsummation()<<" ";
   }
   cout<<endl<<endl;

// 10, 40, 90, ...., 1000 respectively

Header* ptr = h3 + 100;// Here we are moving our pointer till 100th address from address in h3

cout <<"Printing pointer h3: " << h3 << endl;

cout <<"Printing pointer ptr: " << ptr << endl;

  

// d. explain the output you see in the following

cout << "Difference " << (ptr - h3) << " objects" << endl;//Because we have added 100 in the address h3 and stores the new address in ptr and now we are subtracting them, that's why we are getting 100 in response

cout << "Difference " << ((char*) ptr - (char *)h3) << " bytes" << endl;//this is the difference in bytes, Because we are using address of 16 bytes that's why the difference in bytes are 16*100=1600

  

}