nothing being outputted to the output file? (ifstream and ofstream)

[donovandc]

I am new to programming and these type of forums so please forgive me if the question asked sounds weird but I am getting the two files that are needed which are "output.txt" and "output_sorted.txt" but when I check them, its just blank.

 #include <iostream>
#include <cmath>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;


double calcDistance(double  x1, double  y1, double  z1, double  x2, double  y2, double  z2) {
	double sqr =((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) + (z1 - z2) * (z1 - z2));
	double dist = (sqrt(sqr));
	 return dist;
}


int main() {

	double x1, x2, y1, y2, z1, z2;
	std::vector<double> dis;
	ifstream fin("input.txt");
	ofstream fout("output.txt");
	double distance;

	while (fin.good()) {
		fin >> x1 >> y1 >> z1 >> x2 >> y2 >> z2;
		distance = calcDistance(x1, y1, z1, x2, y2, z2);
		dis.push_back(distance);
		fout << x1 << " " << y1 << " " << z1 << " " << x2 << " " << y2 << " " << z2 << " distance = " << distance << endl;
	}

	sort(dis.begin(), dis.end());
	ofstream fout2("output_sorted.txt");
	for (vector<double>::iterator itr = dis.begin(); itr != dis.end(); ++itr)
    fout2 << *itr <<endl;
return 0;

}
	

[jonnin]

change line 34 to cout, do you get anything?
same up above, print what should go into the file, make sure its printing something.

[TheIdeasMan]

Also, learn how to use a debugger, keep an eye on the values of the variables as you step through the code 1 line at a time. See if the vector is populated.

Just be careful with line 26, there is an existing std::distance , it may not have an effect here (I haven't tested it), I like to avoid anything that is already in std:: To fix this get rid of line 6 and put std:: before each std thing (sqrt, ifstream, ofstream, sort)

Ideally one should put their own code into it's own namespace, that is what they are for.

https://en.cppreference.com/w/cpp/language/namespace
https://en.cppreference.com/w/cpp/language/namespace_alias

It's usually a good idea to test if a file was opened, regardless.

There is a std::hypot which you could use instead of your calcDistance function if you wish.
https://en.cppreference.com/w/cpp/numeric/math/hypot

Instead of iterator in line 33, one could do this (range based for loop):

for (const item& : dis) {
     fout2 << item <<endl;
}

[George P]

Either use a range-based for loop, as suggested by TheIdeasMan, or if you want to use iterators in a for loop consider using auto to let the compiler properly type the loop variable, and use the vector's constant interators for the beginning and end when not modifying the contents:

for (auto itr = dis.cbegin(); itr != dis.cend(); ++itr)

(C++11 needed for the const iterators)

Having using namespace std; is going to bite you in the butt sooner or later, it bypasses the reasons why namespaces were introduced, and can be seen as being lazy.
https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice

[George P]

Another take on why using namespace std; shouldn't be used:

https://isocpp.org/wiki/faq/coding-standards#using-namespace-std

The key take-away:

The using-directive exists for legacy C++ code and to ease the transition to namespaces, but you probably shouldn’t use it on a regular basis, at least not in your new C++ code.

[mbozzi]

ISOCPP FAQ wrote:

But either way is fine. Just remember that you are part of a team, so make sure you use an approach that is consistent with the rest of your organization.

https://isocpp.org/wiki/faq/coding-standards#using-namespace-std

Hmm. What is the benefit of consistency in this case?

[TheIdeasMan]

For those that don't like typing std:: everywhere, consider setting up code snippets in your favorite IDE.

I have them so it will write the whole container or algorithm with const as well. The mnemonics is up to the user. I have csstr meaning const std::string and csvec meaning const std::vector<> The 's' means std, I could 'b' there to mean something from boost.

As for using std::cout; it wasn't long before that gave me the shits as well, it's a pain to write lots of those types of statements in the file.

[mbozzi]

I just have a keybinding where Alt-M directly inserts the text std::

[seeplus]

L24/25 is usually written as :

while (fin >> x1 >> y1 >> z1 >> x2 >> y2 >> z2) {

Also it's good practice to check that files have been opened ok before reading/writing them.

After L21 something like:

if (!fin || !fout)
    return (std::cout << "Cannot open files\n"), 1;