CODEWITHSUNDEEP
c++functionpointers
Hugo Perea
Hugo Perea

Reputation: 465

C++ - How to pass an object with a pointer in a function by reference?

How do I pass an object that has a pointer member inside it to a function? I want to be able to modify that objects member and have the original object in main have the modified value reflected upon it, Simple code I just want to know how to do this. I'm new. I made this code as simple as I code, I tried an overloaded assignment operator and a copy constructor but still no good. Can someone explain to me the process that happens when I call the function set(); and why I am getting an error

i want to use the set() function to change the objects name member to a different one

#include <iostream>
#include <string>
using namespace std;

class student
{
public:
    void setName(string *nameVariable);
    void printName(){ cout << *name; }
private:
    string *name;
};

void student::setName(string *nameVariable)
{
    name = nameVariable;
}



void  set(student& student1);

int main()
{
    string *nameptr, name;//creates pointer and varible of type string
    nameptr = &name;//sets nameptr to the adress of name                
    *nameptr = "Nick";//inderict access, assigns what nameptr is pointing to the value"nick"        

    student student1;
    student1.setName(nameptr);
    student1.printName();//couts - Nick -

    set(student1);
    student1.printName();//should cout - Jorge - after modification however an error occurs
    cout << endl;
    system("pause");
}



void  set(student& rightStudent)
{
    string *nameptr, name;
    nameptr = &name;
    *nameptr = "Jorge";
    student localStudent;
    localStudent.setName(nameptr);

    rightStudent = localStudent;
}

Upvotes: 1

Views: 85

Answers (1)

R Sahu
R Sahu

Reputation: 206577

The main problem is that after the function set returns, student1 points to a dangling pointer. Inside the function, rightStudent points to the address of name. That address is invalid once the function returns. Hence, you are seeing undefined behavior.

The program is very brittle. You are storing a pointer but there isn't enough logic to make sure that the pointer remains valid as long as the object (of type student) is alive.

To make things simple, you should store an object instead of a pointer in student.

class student
{
   public:
      void setName(string  const& nameVariable);
      void printName(){ cout << name; }
   private:
      string name;
};

Once you change that, the rest of your program becomes simpler.

void student::setName(string const& nameVariable)
{
    name = nameVariable;
}

void  set(student& student1);

int main()
{
    string name = "Nick";

    student student1;
    student1.setName(name);
    student1.printName();

    set(student1);
    student1.printName();
    cout << endl;
    system("pause");
}

void  set(student& rightStudent)
{
    string name = "Jorge";
    rightStudent.setName(name);
}

Upvotes: 1

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