overloading operator+ (C++)

Question

Hey so I am working on an overload of +, but when I try to do a simple call like

statistician a,b,c;

a = b+c;

When I do the above call it crashes. and if i do an overload of =, it just returns a zero. here is some of my code. Thanks for the help guys!!!

FYI next_number(double value), increases the dynamic array by 1, and puts that value in end of the array.

statistician operator+(const statistician& left, const statistician& right) { statistician temp; if(left.m_iArraySize == 0) { return right; } else if(right.m_iArraySize == 0) { return left; } else { statistician temp; for(int i =0; i< left.m_iArraySize; i++) { temp.next_number(left.m_dSeqArray[i]); } for(int i =0; i< right.m_iArraySize; i++) { temp.next_number(right.m_dSeqArray[i]); } return temp; } }

The Implementation of the class

#include "Statistician.h" #include <iostream> using namespace std; namespace main_savitch_2C { statistician::statistician() { m_iArraySize=0; m_dSeqArray = new double[1]; // Preset our list to 1 items m_dSeqArray[0] = 0; } statistician::~statistician() { delete[] m_dSeqArray; m_iArraySize=0; } statistician::statistician(const statistician &s) { m_iArraySize=0; m_dSeqArray = new double[1]; // Preset our list to 1 items m_dSeqArray[0] = 0; } int statistician::ChangeArraySize(int iArraySize) { double *iTempArray; iTempArray = new double[m_iArraySize]; //Assert Data assert(iArraySize >-1); // Copy the info of the array into a temp array for(int i = 0; i < m_iArraySize-1; i++) { iTempArray[i] = m_dSeqArray[i]; } // iTempArray = m_dSeqArray; // delete the array delete[] m_dSeqArray; m_dSeqArray = new double[iArraySize]; // Copy the info of the temp array back into the orginal array variable for(int i = 0; i < m_iArraySize; i++) { m_dSeqArray[i] = iTempArray[i]; } m_dSeqArray[iArraySize-1]=0; // Free our TempArray delete[] iTempArray; return 0; } //length int statistician::length() const { if(m_iArraySize == 0) {return 0;} return m_iArraySize; } //sum() double statistician::sum() const { if(m_iArraySize == 0) {return 0;} long double dSum=0; for(int i = 0; i < m_iArraySize; i++) { dSum = dSum + m_dSeqArray[i]; } return dSum; } //mean() double statistician::mean() const { if(m_iArraySize == 0) {return 0;} double dSum,dMean; int iCounter; dSum=0; dMean=0; iCounter=0; for(int i = 0; i < m_iArraySize; i++) { dSum = dSum + m_dSeqArray[i]; iCounter++; } // Check for Dividing by zero if(dSum == 0) { dMean = 0; } else { dMean = dSum/iCounter; } return dMean; } //reset() int statistician::reset() { delete[] m_dSeqArray; m_iArraySize = 0; m_dSeqArray = new double[1]; m_dSeqArray[0] = 0; return 0; } //next_number(i) int statistician::next_number(double iValue) { // Ensure that size of the array has not somehow become negative m_iArraySize++; if(m_iArraySize > 1) { ChangeArraySize(m_iArraySize); m_dSeqArray[m_iArraySize-1] = iValue; } else { m_dSeqArray[m_iArraySize-1] = iValue; } return 0; } //next_number(int iValue) int statistician::next_number(int iValue) { m_iArraySize++; if(m_iArraySize > 1) { ChangeArraySize(m_iArraySize); m_dSeqArray[m_iArraySize-1] = iValue; } else { m_dSeqArray[m_iArraySize-1] = iValue; } return 0; } //next_number(char iValue) in case a character is passed int statistician::next_number(char iValue) { cout << "Invalid value passed to next_number!" <<endl; return 0; } //Minimum double statistician::minimum() const { if(m_iArraySize == 0) {return 0;} double dMinimum = m_dSeqArray[0]; for(int i = 0; i < m_iArraySize; i++) { if(m_dSeqArray[i] < dMinimum) { dMinimum = m_dSeqArray[i]; } } return dMinimum; } //Maximum double statistician::maximum() const { if(m_iArraySize == 0) {return 0;} double dMaximum = m_dSeqArray[0]; for(int i = 0; i < m_iArraySize; i++) { if(m_dSeqArray[i] > dMaximum) { dMaximum = m_dSeqArray[i]; } } return dMaximum; } //Operator Overloading /* statistician statistician::operator=( statistician& left) { cout << left.sum(); cout << left.length(); cout << this->sum(); if(this != &left) { this->reset(); for (int i =0; i < left.m_iArraySize; i++) { this->next_number(left.m_dSeqArray[i]); cout<<this->next_number(left.m_dSeqArray[i]) <<endl; cout<<left.next_number(left.m_dSeqArray[i]) <<endl; } } return *this; } */ statistician operator+(const statistician& left, const statistician& right) { statistician temp; if(left.m_iArraySize == 0) { return right; } else if(right.m_iArraySize == 0) { return left; } else { statistician temp; for(int i =0; i< left.m_iArraySize; i++) { temp.next_number(left.m_dSeqArray[i]); } for(int i =0; i< right.m_iArraySize; i++) { temp.next_number(right.m_dSeqArray[i]); } return temp; } } bool operator==( const statistician& left,const statistician& right) { cout << "L length = : "<<left.length() <<" R Length: "<< right.length()<<endl; if(left.length() != right.length()) { return false; } cout << "L minimum = : "<<left.minimum() <<" R minimum: "<< right.minimum()<<endl; if(left.minimum() != right.minimum()) { return false; } cout << "L maximum = : "<<left.maximum() <<" R maximum: "<< right.maximum()<<endl; if(left.maximum() != right.maximum()) { return false; } cout << "L sum = : "<<left.sum() <<" R sum: "<< right.sum()<<endl; if(left.sum() != right.sum() ) {return false; } cout << "L mean = : "<<left.mean() <<" R mean: "<< right.mean()<<endl; if(left.mean() != right.mean() ) {return false; } return true; } } // End of Namespace

and the .h....

#ifndef StatClass #define StatClass #include <cassert> namespace main_savitch_2C { class statistician //With copy constructor { public: // Constructor statistician(); //Deconstructor ~statistician(); //Copy constructor statistician(const statistician &s); //length int length() const; //sum() double sum() const; //mean() double mean() const; //reset() int reset(); //next_number(i) int next_number(double iValue); int next_number(int iValue); int next_number(char iValue); //Minimum double minimum() const; //Maximum double maximum() const; //Operator Overloading //statistician operator=(statistician& left); friend statistician operator+(const statistician& left, const statistician& right); friend bool operator==(const statistician& left, const statistician& right); private: // Private Variables double *m_dSeqArray; int m_iArraySize; // Private Functions int ChangeArraySize(int iArraySize); }; }; #endif

What do the constructor and member variables of statistician look like? Does the constructor initialize m_iArraySize? — Steve Jessop
– Steve Jessop, Commented Aug 29, 2010 at 21:07
It's impossible to tell what's happening without the full code. A verbal description of what some of the missing code does is not very useful when the entire question is here solely because your code does not do what you expect. — Steve Townsend
– Steve Townsend, Commented Aug 29, 2010 at 21:07
Please post the code for statistician's default constructor, this is relevant to the behaviour of the code that you have posted. Also, what is the type of m_dSeqArray? — johnsyweb
– johnsyweb, Commented Aug 29, 2010 at 21:11
Your code will be considerably simpler and less error-prone if you change m_dSeqArray to a std::vector<double>. — Steve Jessop
– Steve Jessop, Commented Aug 29, 2010 at 22:46

Beta · Accepted Answer · 2010-08-29 22:03:01Z

If you don't define the assignment operator (operator=), then the compiler provides a default version, which does a shallow copy-- that is, it copies the pointer m_dSeqArray, but not the thing it points to. So when you use it, you wind up with two pointers pointing to the same thing. When the two statisticians pass out of scope, each calls the destructor, which tries to delete the array twice, BOOM!

Your version of the assignment operator copies each element twice:

this->next_number(left.m_dSeqArray[i]); cout<<this->next_number(left.m_dSeqArray[i]) <<endl;

So the resultant statistician should look weird, but not be empty (unless the statistician being assigned was empty, which it is in your example).

Gorpik · Accepted Answer · 2010-08-29 22:01:42Z

First, the canonical operator+ should be implemented in terms of operator+=, and it is in this operator that you should write your logic.

Second, statistician copy constructor does not copy anything, it just creates a default statistician. Since operator+ uses the copy constructor for its return value, you will never get what you intend.

Third, statistician::next_number() does not do what you think. You never increase the size of the internal array, so you will end up going out of bounds. This leads to undefined behaviour, probably crashing when you overwrite memory belonging to other objects.

I have not checked all the code for all methods, but you should definitely fix these three errors before continuing. Well, the first one is not so important, but the other two ones are a must.

so the ChangeArraySize(m_iArraySize), that i am calling in next_number is not increasing it? As for the copy constructor, i do not think i am effectively writing it, i have changed it to this: m_iArraySize= s.m_iArraySize; m_dSeqArray = new double[1]; but since the operator+ uses the copy constructor, does that mean this see's m_dSeqArray as an array of [0]. with initialize value forever?
Since m_iArraySize is one less than the actual array size, you end up just nullifying the value of the last element in the array in ChangeArraySize(). And if you were not actually implementing the copy constructor, your copy would share the original object internal array. When you delete that array in the original object destructor (upon leaving operator+), you end up with a deleted array in the copy (a recipe for disaster). Your new implementation does not crash, but it does not copy the array either.

Chubsdad · Accepted Answer · 2010-08-30 02:44:04Z

Though not a direct reason for crash, I can't help pointing it out

The copy constructor looks to be a cut-paste of the constructor. This may not be right I believe. Copy constructor may be involved since operator+ involves returning a copy which could call copy constructor if it is not elided away.

How are you using 's' in the copy constructor?

statistician::statistician(const statistician &s) { m_iArraySize=0; m_dSeqArray = new double[1]; // Preset our list to 1 items m_dSeqArray[0] = 0; }

Collectives™ on Stack Overflow

overloading operator+ (C++)

3 Answers 3

Comments

2 Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

Comments

Linked

Related