EXC_BAD_ACCESS when adding object to array - c++

Question

I am new programming and C++. I am trying to create a Roster of Person objects using an array and then printing the attributes of the People in the Roster.
When I attempt to add a Person to the personArray, I am getting an
Exception = EXC_BAD_ACCESS (code=1, address=0x0).
I think this has to do with the scope of my personArray but I can't seem to figure it out.
Here is the code I am using:
#include <iostream>
#include <sstream>
#include <vector>
using namespace std;
class Person
{
public:
Person(string name, int age);
string getName() {
return name;
}
void setName(string n) {
name = n;
}
int getAge() {
return age;
}
void setAge(int a) {
age = a;
}
private:
string name;
int age;
};
class Roster {
public:
void addToPersonArray(string name, string age) {
Person person(name, stoi(age));
personArray[personCount] = &person;
}
void printPersonArray() {
for (int i = 0; i < 5; i++)
cout << personArray[i]->getName() << '\t' << personArray[i]->getAge() << '\n';
}
private:
Person *personArray[5];
int personCount = 0;
};
int main() {
const string studentData[] = {"Dan,45", "Mark,33", "Mary,22",
"April,17", "Jill,22"};
Roster roster;
stringstream ss(studentData[0]); // just testing the first entry
vector<string> result;
while (ss.good()) {
string substr;
getline(ss, substr, ',');
result.push_back(substr);
}
roster.printPersonArray();
}

Answer 1

The problem is here:
void addToPersonArray(string name, string age) {
Person person(name, stoi(age));
personArray[personCount] = &person;
}
person is a local variable in the member function addToPersonArray(), which will be destroyed after the function scope.
Hence, storing the address of a local variable(and trying to accessing it latter in printPersonArray()) will give you, nothing but an undefined behavior.
You are lucky that your programme got the exception.
One more thing to note that, you are not actually using your roster to test the program. Instead, all you do is parsing and saving to result vector. You can add this after the while loop, to make it actually work.
if (result.size() == 2) {
roster.addToPersonArray(result[0], result[1]);
}
Suggestion: Since you have a fixed array size, you probably wanna do it with std::array<Person, 5> or with std::vector<Person> by reserving the memory for 5 Person in the c'tor of Roster.
See a sample output: https://wandbox.org/permlink/tAGqqnhCfwz1wPrH
#include <iostream>
#include <sstream>
#include <vector>
#include <array>
class Person {
public:
Person(const std::string& name, int age): name(name), age(age) {}
std::string getName()const { return name; }
void setName(const std::string& n){ name = n; }
int getAge()const { return age; }
void setAge(int a) { age = a; }
private:
std::string name;
int age;
};
class Roster {
public:
Roster() { personArray.reserve(5); } // reserve some memory
void addToPersonArray(const std::string& name, const std::string& age) {
personArray.emplace_back(name, stoi(age));
}
void printPersonArray() {
// use range loop, which will assure, access what you have.
for (const Person& person: personArray)
std::cout << person.getName() << '\t' << person.getAge() << '\n';
}
private:
std::vector<Person> personArray;
//int personCount = 0; --------------> no need anymore
};
int main() {
std::array<std::string,5> studentData{ "Dan,45", "Mark,33", "Mary,22", "April,17", "Jill,22" };
Roster roster;
for(const std::string& str: studentData)
{
std::stringstream ss(str);
std::vector<std::string> result;
while (ss.good()) {
std::string substr;
std::getline(ss, substr, ',');
result.emplace_back(substr);
}
if (result.size() == 2) {
roster.addToPersonArray(result
[0], result[1]);
}
}
roster.printPersonArray();
return 0;
}
Output:
Dan 45
Mark 33
Mary 22
April 17
Jill 22

Answer 2

In addition to storing pointers to local variables in your addToPersonArray() function, your main() function does not add any entries to the personArray.
Instead, main creates a Roster object, and after some code that doesn't affect anything with Roster, you go straight into calling roster.printPersonArray, which does this:
void printPersonArray()
{
for (int i = 0; i < 5; i++) // <-- This will loop for all 5 entries
cout << personArray[i]->getName() << '\t' << personArray[i]->getAge() << '\n';
}
Since personArray was never initialized to contain valid pointers to Person objects, that loop will cause undefined behavior.
The issue is that you have a personCount member variable, but fail to make use of it to control how many valid entries there are in the array. The loop should have been written as below:
void printPersonArray()
{
for (int i = 0; i < personCount; i++)
cout << personArray[i]->getName() << '\t' << personArray[i]->getAge() << '\n';
}
In addition to the storage of pointers to local variables, your Roster::addToPersonArray() doesn't check if personCount is greater than 4, thus this is another place in your code where you failed to use personCount to control how many Person objects are being referenced.