Why am I getting a Segmentation fault: 11 in my C++ program? - c++

Question

I am currently experiencing trouble with an Segmentation fault : 11 in my C++ Program which uses object-oriented concepts:
//
// main.cpp
// pointersInOOP
//
// Created by Jayant Raul Rao on 15/05/15.
// Copyright (c) 2015 Jayant Raul Rao. All rights reserved.
//
#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;
class Student
{
public:
char * name;
int semesterHours;
float gpa;
};
int main(int argc, const char * argv[]) {
cout<<"Beta Version of 1.0 Student constructor. \n";
cout<<"\n";
cout<<"\n";
//Declaring a student object and a pointer
Student s;
Student *pOnS = &s;
//take userInput
printf("Please name the student... : ");
cin>>pOnS->name;
printf("Okay, you called your Student %s. Please now input the gpa of the Student: ", pOnS->name);
cin>>pOnS->name;
printf("The gpa of %s is %f", pOnS->name, pOnS->gpa);
return 0;
}
And when I execute this code I actually give my input and that always ends in a Segmentation fault. This error I get if I execute in the Terminal. If I execute directly in Xcode I get directed to a file called istream where there is written at a line: Bad access 0x1. Therefore I am unable to execute my program. I have already found out what Segmentation fault means.
Something like literally Stack Overflow. But I am unable to really understand any bugfix.
I thank you in advance,
Jayant Raul Rao

Answer 1

This code is un tested, but the main point is that it would be easier if you use a String type for the student name. So if you change char *name to std::string name your code will work.
If you want to stick to using char then you have to do something like this.
#include <string>
...
//take userInput
printf("Please name the student... : ");
std::string name;
cin>>name;
pOnS->name = new char(name.size() + 1);
strncpy(pOnS->name, name.c_str(), name.size());
pOnS->name[name.size() + 1] = '\0';
P.S fix this:
printf("Okay, you called your Student %s. Please now input the gpa of the Student: ", pOnS->name.c_str()); <-- if using String type
cin>>pOnS->gpa; //<----

Answer 2

class Student
{
public:
char * name; //you are not allocating memory for this.
int semesterHours;
float gpa;
};
You could use a character array like char name[15] or std::string
Also you are not initializing gpa before printing it.

Answer 3

A segmentation fault indicates some sort of invalid memory access. In this case, you're declaring a pointer (char * name), but never initializing it. So it points to some arbitrary value, which may or may not be a valid memory address. Then you try to write through it: cin>>pOnS->name;. This is undefined behaviour, which is likely to result in one of the following:
If the pointer's value is not a valid writable memory address, then you'll get a crash right away; the error that you'll get depends on the OS, but the most common ones are "segmentation fault", "general protection fault", or "bus error".
If the pointer's value is a valid writable memory address, then you'll overwrite whatever happens to be there. This may seem to work correctly, only for it to crash unpredictably when you try to run your program on a different computer, or at a different time. Or it may corrupt something that your program will try to use later, resulting in a crash in unrelated code.
To avoid this problem, ensure that you always write to valid memory locations. The easiest way to do that in this case is to use std::string rather than a raw character array.
Also, I think that your second write to pOnS->name should actually be to pOnS->gpa.

Answer 4

pons = new student;
Use the above statement after declaring pons as an object reference in the function. Rest looks fine and it worked for me hope it does for you too.