Question

This is my source file written in C++.

#include<string>
#include<sstream>
#include "Lecture.hpp"
#include <iostream>

using namespace std;


Lecture::Lecture() {
  capacity=5;
  log = new int[capacity];
  used = 0;
}

/*
 * The following is copy constructor.
 */
Lecture::Lecture(Lecture& orig) {
   copy(&orig);

}

/*
 * This is an empty destructor
 */
Lecture::~Lecture() {
    // dereference dynamic memory
}

 Lecture & Lecture:: operator=(Lecture & other){
     this->copy(&other);
     return *this;
 }
 /*
  * Copy method.
  */
 void Lecture::copy(Lecture &other){    
     if(&other != this){
         capacity = other.capacity;
         log = new int[capacity];
         used = other.used;
         for(int x = 0; x < used; x++){
            log[x]= other.log[x]; 
         }
     }
 }

string Lecture::getLogs() {
  ostringstream ans;
  ans << "[";
  for (int i=0; i<used-1; ++i) {
    ans << log[i] <<", ";
  }
  if (used>0) 
    ans << log[used-1] << "]";
  else
    ans << "empty log]";
  return ans.str();
}

void Lecture::addLogEntry(int b) {
   if (used==capacity) {
    capacity *= 2;
    int* temp= new int[capacity];
    for (int i=0; i<used; ++i) {
      temp[i]=log[i];
    }
    delete[] log;
    log=temp;
  }
  log[used]=b;
  used++;
}

From copy constructor and from overloaded = operator function I am trying to invoke copy() function. It gives me the following error:

Lecture.cpp: In copy constructor `Lecture::Lecture(Lecture&)':
Lecture.cpp:26: error: no matching function for call to `Lecture::copy(Lecture*)'
Lecture.hpp:21: note: candidates are: void Lecture::copy(Lecture&)
Lecture.cpp: In member function `Lecture& Lecture::operator=(Lecture&)':
Lecture.cpp:38: error: no matching function for call to `Lecture::copy(Lecture*)'
Lecture.hpp:21: note: candidates are: void Lecture::copy(Lecture&)
make[2]: Leaving directory `/cygdrive/g/Aristotelis/C++/Assessment_2'
make[1]: Leaving directory `/cygdrive/g/Aristotelis/C++/Assessment_2'
make[2]: *** [build/Debug/Cygwin-Windows/Lecture.o] Error 1
make[1]: *** [.build-conf] Error 2
make: *** [.build-impl] Error 2 

For some reasons at copy method it expects a pointer. Why is that?
This is my header file:

#ifndef LECTURE_HPP
#define LECTURE_HPP

#include<string>
using namespace std;

class Lecture{ 

 public : 
  Lecture();                 // default constructor
  Lecture(Lecture &other);  // copy constructor
  string getLogs();
  void addLogEntry(int);
  void copy(Lecture &other); // copy method
  ~Lecture();                // destructor
  Lecture& operator=(Lecture& other); // overloading of '='

 private: 
  int* log;
  int used;
  int capacity;



};

#endif  /* LECTURE_HPP */

This is main method:

#include<iostream>
#include<string>
//#include "University.hpp"
#include <cmath>
#include <cstdlib>



using namespace std;

/*
 * 
 */
int main(int argc, char** argv) {


  Lecture c1;

  cout << "Information of c1: " <<c1.getLogs() << endl;

  c1.addLogEntry(20);

  cout << "Information of c1: " <<c1.getLogs() << endl;

  Lecture c2=c1;

  cout << "Information of c2: " <<c2.getLogs() << endl;

  Lecture c3;
  c3=c1;

  cout << "Information of c3: " <<c3.getLogs() << endl;

  c1.addLogEntry(-4);
  c2.addLogEntry(10);

  cout << "-----------------------------------------------"<< endl;

  cout << "Information of c1: " <<c1.getLogs() << endl;
  cout << "Information of c2: " <<c2.getLogs() << endl;
  cout << "Information of c3: " <<c3.getLogs() << endl;


    return 0;
}

What might be the problem?

Answer 1

Because you are passing a pointer:

Lecture::Lecture(Lecture& orig) {
   copy(&orig);  // The & here is taking the address of orig (so remove it!)
}

[Sidenote 1: Unless you have a very good reason, your copy constructor, etc. should prefer to take a const ref over a non-const ref.]

[Sidenote 2: See this question for the idiomatic way to implement copy-constructor and copy-assignment operators in C++.]