*** glibc detected *** double free or corruption (fasttop): 0x09499008 ***

[adjoiningPanda]

Hello fellow programmers. I am new to c++ and also fairly new to programming. I have been given an assignment to create a class called Doctor. The user inputs a number of patients and patient names for the doctor and the program prints them out along with several supporting other functions. However, I am having a problem. At the end of the run (which is correct), I receive the following error: *** glibc detected *** double free or corruption (fasttop): 0x09499008 ***. Can any one tell me what is happening? Here is my code:

#include <iostream>
#include <string>
#include <assert.h>
//#define PRODUCT_VERSION

using namespace std;

//Doctor class
class Doctor {
public:
		//Doctor Constructor and Destructor
        Doctor();
        ~Doctor();

		//public variables 
        string name; //name of Doctor
        int numPatients; //number of patients
        string* patientList; //list of patients

		//asks user to input public variables
        void askUserInput();
		//prints doctor's patient list and returns number of prints
		//for testing purposes
        int printPatients();
		//resets the number of patients to zero and the patientList to an
		//empty list
        void reset();

		//overloads the ++ operator to create a copy of the patientList
        void operator++();
};

//make Doctor instance for testing
Doctor docLow;
Doctor docMid;
Doctor docHigh;
//make Doctor list copy
string* copyList;

int main()
{
	

	//if defined, product version is executed with user input.
	//otherwise, testing is executed with pre-defined boundary inputs
#ifdef PRODUCT_VERSION

#else
	//Unit Testing
	cout << "*** UNIT TESTING for Doctor class ***\n\n";
	//boundary tests
	int i = 0;
	//tests 3 cases
	while (i < 3)
	{
		switch (i) 
		{
			case 0:
				{
					//Empty case
					cout << "Testing Low Boundary...\n\n";
					docLow.name = "Empty";
					docLow.numPatients = 0;
					docLow.patientList = new string[docLow.numPatients];
					runTests(docLow);
					docLow.patientList = NULL;
					i++;
					break;
				}
			case 1:
				{
					//Middle case
					cout << "\nTesting Middle Boundary...\n\n";
					docMid.name = "Medium";
					docMid.numPatients = 5;
					docMid.patientList = new string[docMid.numPatients];
					//predefined patientList
					docMid.patientList[0] = "Amanda";
					docMid.patientList[1] = "Bradley";
					docMid.patientList[2] = "Charlie";
					docMid.patientList[3] = "Doug";
					docMid.patientList[4] = "Eno";
					runTests(docMid);
					docMid.patientList = NULL;
					i++;
					break;
				}
			case 2:
				{
					//Long Case
					cout << "\nTesting High Boundary...\n\n";
					docHigh.name = "Long";
					docHigh.numPatients = 10;
					docHigh.patientList = new string[docHigh.numPatients];
					//predefined patientList
					docHigh.patientList[0] = "Amanda";
					docHigh.patientList[1] = "Bradley";
					docHigh.patientList[2] = "Charlie";
					docHigh.patientList[3] = "Doug";
					docHigh.patientList[4] = "Eno";
					docHigh.patientList[5] = "Fran";
					docHigh.patientList[6] = "Gabriel";
					docHigh.patientList[7] = "Hannah";
					docHigh.patientList[8] = "Ico";
					docHigh.patientList[9] = "Jack";
					runTests(docHigh);
					docHigh.patientList = NULL;
					i++;
					break;
				}
		}
	}
#endif
}


//Doctor destructor
Doctor::~Doctor()
{
		numPatients = 0;
		//allocated memory is deleted
		delete [] patientList;
		patientList = NULL;
}

void Doctor::askUserInput()
{
		//Asks user for doctor name
        cout << "What is the doctor's name?: " ;
        getline(cin, name);
        cout << endl;

		//Asks user for number of patients
        cout << "Enter the number of patients the doctor has: ";
        cin >> numPatients;
        string getEnter;
        getline(cin, getEnter);
        cout << endl;

		//allocates memory for dynamic string
        patientList = new string[numPatients];

		//Asks user for each patient's name
        cout << "Enter each patient's name.\n\n";

        for (int i = 0; i < numPatients; i++)
        {
			cout << "Patient " << i + 1 << ": ";
			getline(cin, patientList[i]);
			cout << endl;
        }

        cout << endl;
}

}

void Doctor::reset()
{
		//resets number of patients to zero
        numPatients = 0;
		//deletes allocated memory
        delete [] patientList;
		//makes empty list
        patientList = new string[numPatients];
}

void Doctor::operator++()
{
		//allocates necessary memory for a copy list
		copyList = new string[numPatients];

		//iterates through patientList and copies each patient to copyList
		for (int i = 0; i < numPatients; i++)
		{
			copyList[i] = patientList[i];
		}
}

bool checkEqualArrays(string array1[], string array2[], Doctor doc)
{
	//iterates through both arrays and ensures they are equal
	int i = 0;
	bool equal = true;
	while(i < doc.numPatients && equal)
	{
		if (array1[i] != array2[i])
		{
			equal = false;
		}
		i++;
	}
	//returns true if equal, false otherwise
	return equal;
}

void runTests(Doctor doc)
{
	//creates local copy variables in order to restore
	//original values when Doctor variables are reset
	string storeName;
	int storeNumPatients;
	string* storePatientList;

	storeName = doc.name;
	storeNumPatients = doc.numPatients;
	storePatientList = new string[doc.numPatients];
	
	for (int i = 0; i < storeNumPatients; i++)
	{
		storePatientList[i] = doc.patientList[i];
	}

	//prints out Doctor's public variables that were either input
	//by the user (checks askUserInput()) or pre-defiend by the programmer 
	cout << "Test results: \n\n";
	cout << "Doctor name: " << doc.name << endl << endl;
	cout << "Number of Patients: " << doc.numPatients << endl << endl;
	cout << "Patient List: \n\n";

	for (int i = 0; i < doc.numPatients; i++)
	{
		cout << doc.patientList[i] << endl << endl;
	}

	cout << "Case passed...\n\n" << endl;

	//Tests the number of patients printPatients() printed
	//and compares to numPatients
	cout << "\nTest for printPatients() function: \n\n";
	assert(true == (doc.numPatients == doc.printPatients()));
	cout << "Case passed...\n\n";

	//Tests reset() to ensure numPatients is equal to zero
	//and patient list is empty
	cout << "Test for reset() function: \n\n";
	doc.reset();
	assert(true == (doc.numPatients == 0));
	doc.printPatients();
	cout << endl;

	cout << "Case passed...\n\n" << endl;

	//restore original values that were recently reset
	doc.name = storeName;
	doc.numPatients = storeNumPatients;
	delete [] doc.patientList;
	doc.patientList = new string[doc.numPatients];

	for (int i = 0; i < doc.numPatients; i++)
	{
		doc.patientList[i] = storePatientList[i];
	}

	//Tests if operator++() function successfully created a 
	//copy of the Patient list
	cout << "Test for operator++() function: \n\n";
	doc.operator++();
    assert(true == (checkEqualArrays(doc.patientList, copyList, doc)));
	
	doc.patientList = new string[doc.numPatients];

	for (int i = 0; i < doc.numPatients; i++)
	{
		doc.patientList[i] = storePatientList[i];
	}

	cout << "Printing copied patient list... \n\n";
	
	for (int i = 0; i < doc.numPatients; i++)
	{
		cout << copyList[i] << endl << endl;
	}

	cout << "Case passed...\n\n";

	//Tests to ensure that Doctor destructor deletes 
	//previous allocated memory
	cout << "\nTest for ~Doctor() function: \n\n";
	doc.~Doctor();

	cout << "Doctor name: " << doc.name << endl << endl;
	cout << "Number of Patients: " << doc.numPatients << endl << endl;
	cout << "List of Patients: " << endl << endl;

	for (int i = 0; i < doc.numPatients; i++)
	{
		cout << doc.patientList[i] << endl << endl;
	}
	
	delete [] storePatientList;
	storePatientList = NULL;
	delete [] copyList;
	copyList = NULL;
	cout << "Case passed...\n\n";
}

[Cubbi]

There are multiple memory management errors. The most obvious one is that the user-defined copy constructor for Doctor is missing, which results in multiple Doctors referring to the same array and, ultimately, double-free. The copy constructor is called each time you invoke runTests() or checkEqualArrays()

There is also a memory leak on line 261

There are still more memory errors after those, that are showing up on memory profiler.


Why are you using arrays instead of vectors?

[adjoiningPanda]

It's a requirement for the assignment to use dynamic arrays. Again, I'm just learning how to program in C++. The reason I continuously allocate new memory is because the destructor was automatically being called and deallocating the array. I have no clue why that is happening.

How do I make a copy constructor? Do you mean overloading the default constructor?

Also, do you recommend I install a memory profiler?