Returning a structure pointer - c++

Question

I'm quite new with c++ and need some help with the following code.
#include <iostream>
using namespace std;
struct student {
string name;
int age;
float marks;
};
struct student *initiateStudent(string , int , float);
int main ( ) {
int totalStudents = 1;
string name;
int age;
float marks;
cin >> totalStudents;
student *stud[totalStudents];
for( int i = 0; i < totalStudents; i++ ) {
cin >> name >> age >> marks;
stud[i] = initiateStudent(name,age,marks);
}
cout << stud[0]->name;
return 0;
}
struct student *initiateStudent(string name, int age, float marks)
{
student *temp_student;
temp_student->name = name;
temp_student->age = age;
temp_student->marks = marks;
return temp_student;
}
I need in the function initiateStudent return a struct pointer to the pointer array stud by passing the members name, age, marks.
I know that the problem sofar is the fact that temp_student is destroyed when I return to the main file.
So my question is how it could be done by just passing the members of the struct and then return back with information to the pointer array stud.
Thank you very much.

Answer 1

Semi-answer To explain the bad habits:
#include <string>
#include <iostream>
#include <vector>
//using namespace std; often injects subtle bugs. Use with caution
// read more here:
// http://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice
struct student
{
std::string name; // explicit namespacing reduces possibility of unwanted collisions
int age;
float marks;
//added constructor in place of initialization function.
student(std::string name, int age, float marks):name(name), age(age), marks(marks)
{
}
};
int main()
{
int totalStudents = 1;
std::string name;
int age;
float marks;
while (!(std::cin >> totalStudents)) // testing input for success
// Needed extra brackets caught by M.M
// teach me to not test even a throw-away example
{
std::cout << "must... have... good... input..." << std::endl;
cin.clear(); // clear the error and get rid of any other garbage the user may have input.
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}
//student *stud[totalStudents]; illegal in C++
std::vector<student *> stud(totalStudents); // using dynamic array instead
for (int i = 0; i < totalStudents; )// i++ removed
{
if (std::cin >> name >> age >> marks) //testing input
{
stud[i] = new student(name, age, marks); // using constructor
i++; // and put here. Only increment if input is valid.
}
else
{
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}
}
std::cout << stud[0]->name;
for (student * stu: stud) // cleaning up allocated memory
{
delete stu;
}
return 0;
}
One of the beauties of C++ is you rarely need to self-manage memory. In fact there are huge advantages in not doing it above and beyond not having to clean up after yourself.
#include <string>
#include <iostream>
#include <vector>
struct student
{
std::string name;
int age;
float marks;
student(std::string name, int age, float marks):name(name), age(age), marks(marks)
{
}
};
int main()
{
std::string name;
int age;
float marks;
std::vector<student> stud; // look ma! No pointer!
while (std::cin >> name >> age >> marks) //exits loop on bad input
{
stud.emplace_back(name, age, marks); // building directly in vector
// vector will size itself as needed.
}
std::cout << stud[0].name;
return 0;
}
One more caveat: >> is whiespace delimited. That means it stops when it finds whitespace (space, tab, end of line...) so a name of "John Jacob Jingleheimer-Shmidt" will go into name as "John". >> will then attempt to interpret "Jacob" as age, and that will not go so well.

Answer 2

the simple solution is to make your initiateStudent() creates temp_student on the heap (with new): and returns it. keep in mind heap allocated memory is not freed automatically so don't forget to free it later on yourself.
#include <iostream>
#include <string>
using namespace std;
struct student {
string name;
int age;
float marks;
};
struct student *initiateStudent(string , int , float);
int main ( ) {
int totalStudents = 1;
string name;
int age;
float marks;
cout << "Total student: ";
cin >> totalStudents;
cin.sync(); // very very important to not affect the next input (name)
student* stud = new student[totalStudents];
for( int i = 0; i < totalStudents; i++ )
{
cout << "Name: ";
getline(cin, name);
cin.sync();
cout << "age: ";
cin >> age;
cout << endl;
cout << "Marks: ";
cin >> marks;
cout << endl;
cin.sync();
stud[i] = *initiateStudent(name, age, marks);
}
cout << "Student 1: " << stud[0].name << endl;
delete[] stud;
stud = NULL;
return 0;
}
struct student *initiateStudent(string name, int age, float marks)
{
student *temp_student = new student;
temp_student->name = name;
temp_student->age = age;
temp_student->marks = marks;
return temp_student;
}