I need help - outputing the values of an array returned from a function

[anthony1947]

Hello,

I am having a slight problem in the main programme outputing the values of the pointer to the array returned by the function generate_planet(ifstream &fin) [Line 56]. At the moment, I can only return the first (of four values) of the array the_planets [Line 92] for every counter increment of 'i' within the main programme. How can I output all the four values of the_planet within the main programme

The content of the input file (route.txt) is:

10
1 9 8 10
2 6 8 3
3 7 8 1
4 1 1 2
5 21 11 6
6 7 11 0
7 11 18 1
8 5 3 1
9 9 9 17
10 8 1 2

The programme I have developed so far is as follows:

#include <iostream>
#include <cmath>
#include <fstream>

class planet
{
public:
// Variables that define the coordinates of the planets
float planet_id;
float x;
float y;
float z;
};

void report_planet (float planet_id, float x_coord, float y_coord, float z_coord)
{
using namespace std;

cout << "Planet's ID: " << planet_id << endl;
cout << "x coordinate: " << x_coord << endl;
cout << "y coordinate: " << y_coord << endl;
cout << "z coordinate: " << z_coord << endl;
cout << "\n";

return;
};

using namespace std;

float generate_planet (ifstream &fin)
{
int j = 0;
float *temp_arr;
temp_arr = new float [4];
for (j=0; j<4; j++)
{
fin >> temp_arr[j];
cout << temp_arr[j] << "\t";
cout << j << endl;
}
return *temp_arr;
delete [] temp_arr;
};

void main()
{
using namespace std;

int i;
int j;
int temp_size;
planet *the_planets[10];

ifstream fin;
fin.open ("route.txt");
fin >> temp_size;
float *temp_array = new float[temp_size];
for (i=0; i<temp_size; i++)
{
float the_planets = generate_planet (fin);
cout << "\n";
cout << the_planets << endl;
report_planet(the_planets, 12, 32, -93);
cout << "\n";
}

delete [] temp_array;
fin.close ();

cin.sync ();
cin.get ();

return;
}

[D80DSL3A]

Yes, there are some problems with your code.
The problems are numerous and intertwined.
It looks like an effort to "force" the program to work has been made.

For starters:

#include <iostream>
#include <cmath>
#include <fstream>
using namespace std;// put this here. No need for it to appear anywhere else. 

Next:
You declare (but never use) an array of 10 planet pointers. I think it's these pointers which
the function generate_planet() is meant to provide values for. It would work if generate_planet allocates an instance of planet, fills it with values from the file then returns a pointer to the planet.

I think the program would work better if you used the following:

ifstream fin;
fin.open ("route.txt");// add code to test for failure here before continuing with the file read
fin >> temp_size;
planet **the_planets = new planet*[temp_size];// creates an array of temp_size planet pointers
for (i=0; i<temp_size; i++)
	the_planets[i] = generate_planet (fin);

Where:

planet* generate_planet(ifstream &fin)
{
	planet* new_planet = new planet;	
	fin >> new_planet->planet_id;
	fin >> new_planet->x;
	fin >> new_planet->y;
	fin >> new_planet->z;
	return new_planet;
}

Then:

for (i=0; i<temp_size; i++)
	report_planet( the_planets[i] );// passing a pointer to planet i 

Where:

void report_planet(planet* a_planet)
{
	cout << "Planet's ID: " <<  a_planet->planet_id << endl;
	cout << "x coordinate: " << a_planet->x << endl;
	cout << "y coordinate: " << a_planet->y << endl;
	cout << "z coordinate: " << a_planet->z << endl;
	cout << "\n";
	return;
}

Finally, release all the memory:

for (i=0; i<temp_size; i++)
	delete the_planets[i];// delete each planet
delete [] the_planets;// delete the array of pointers 

EDIT: Note that planet** the_planets is to replace planet* the_planets[10].

[anthony1947]

Brilliant! it works; Thank you. Yours is an excellent interpretation of what I was attempting to do, without any issues and it looks so simple. Can you advise me on any books that I can use to polish my skills in C++ programming, including good coding practice?

[ne555]

Hi, you should use objects instead of pointers.

fin >> temp_size;
std::vector<planet> the_planets(temp_size);// creates an array of temp_size planets 

planet generate_planet(ifstream &fin)
{
	planet new_planet;
	//fill the data
	return new_planet;
}

Also: main must return int

[anthony1947]

Thanks Ne555! I will try the implementation for array creation that you have suggested.