Copying Array - Crashes After Doubling Array - c++

Question

I'm having some trouble with this program, I'm aware I can use a vector but I'm trying to do it only using arrays. Once the program gets to the initial array size of 1000, it should double the array (in this case to 2000) after copying the data. So for example if I had a list of 3000 names, it'd double once at 1000, then again at 2000 - making the total list 4000. I'm not entirely sure why it crashes after I double the array size. Can someone help me with this?
#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;
struct Information {
char functionality;
string SSN;
string name;
};
Information* person;
int numPeople = 1000;
int numRetrieved = 0;
int numArray = 0;
int numInserted = 0;
int numDeleted = 0;
void doubleArray(Information *person){
numPeople = numPeople * 2;
Information* temp = new Information[numPeople];
memcpy(temp, person, numPeople/2);
delete[] person;
person = temp;
cout << "Person 1: " << person[0].name << " " << person[0].SSN << endl;
}
//Currently not using this until I figure out the double...
void halfArray(Information *person){
numPeople = numPeople / 2;
}
void deleteInfo(Information *person, string SSN){
for(int i = 0; i < numArray; i++){
if(person[i].SSN == SSN){
for(int k = i; k < numArray-1; k++){
person[k].SSN = person[k+1].SSN;
person[k].name = person[k+1].name;
}
numArray--;
numDeleted++;
if((numArray+1) < (numPeople / 4)){
//halfArray(person);
}
}
}
}
void retrieve(Information *person, string findSSN, int lastPerson){
for(int i = 0; i < lastPerson; i++){
if(person[i].SSN == findSSN){
numRetrieved++;
}
}
}
void insert(Information *person, string SSN, string name){
if(numArray == (numPeople - 1)){
doubleArray(person);
}
bool dontInsert = false;
for(int i = 0; i <= numArray; i++){
if(person[i].SSN == SSN){
dontInsert = true;
}
}
if(dontInsert){
dontInsert = false;
}else{
person[numArray].SSN = SSN;
person[numArray].name = name;
numArray++;
numInserted++;
}
}
int main(int argc, char* argv[]) {
person = new Information[numPeople];
char firstLetter;
string SSN, firstName, lastName, name;
fstream input(argv[1]);
for(int i = 0; !input.eof(); i++){
input >> firstLetter >> SSN >> firstName >> lastName;
name = firstName + " " + lastName;
switch(firstLetter){
case 'd':{
deleteInfo(person, SSN);
break;
}
case 'i':{
insert(person, SSN, name);
break;
}
case 'r':{
retrieve(person, SSN, numArray);
break;
}
}
}
input.close();
}

Answer 1

You delete the memory that the Information* points at, but you have a copy of that pointer, and assigning it to your temp variable has no effect outside of doubleArray.
Let's say that the value of person passed in is 0xC001C001;
void doubleArray(Information *person){
numPeople = numPeople * 2;
Information* temp = new Information[numPeople];
memcpy(temp, person, numPeople/2);
delete[] person;
person = temp;
cout << "Person 1: " << person[0].name << " " << person[0].SSN << endl;
}
You create a new pointer temp which has a value of 0xBAD1BAD1. You delete person (0xC001C001), then assign 0xBAD1BAD1 to person. Execution then continues in the insert function ...
void insert(Information *person, string SSN, string name){
if(numArray == (numPeople - 1)){
doubleArray(person);
}
bool dontInsert = false;
for(int i = 0; i <= numArray; i++){
if(person[i].SSN == SSN){
dontInsert = true;
}
}
The person variable here still has the value 0xC001C001, which has been deallocated. Your program blows up when you deference person with person[i].SSN.
When you want to change a pointer, the classic pattern is to pass a pointer pointer. (Two star programming)
void redo(P** p)
{
P* temp = new P();
delete *p;
*p = temp;
}