Call to non-static member function without an object argument compiler error

Question

I am working on a project for my intro to c++ class which is to build a program to calculate various statistics. I have the calculations down, but our professor wants us to use std::istream to collect the input from a file. The program will keep collecting information from the file until it reaches an End of File marker. I am very unfamiliar with the way std::istream works and I keep encountering this error when I try to compile.

main.cpp:5:10: error: call to non-static member function without an object argument stats::getInput(std::cin);

Here is my stats.cpp file:

#include "stats.h"
#include <vector>
#include <cstdlib>
#include <iostream>

stats::stats(){
}

std::vector <double> stats::getInput(std::istream& input_stream){

  std::vector <double> stream;
  double x;

  while(input_stream){

    input_stream >> x;
    // std::cout << "your list of numbers is: " << x << std::endl;

    if(input_stream){
      stream.push_back(x);
    }

  }

  return stream;
}

Here is my header file:

#ifndef _STATS_
#define _STATS_
#include <vector>
#include <cstdlib>

class stats{

 public:
  stats();
  std::vector <double> getInput(std::istream& input_stream);

 private:



};

#endif

and here is my main.cpp file:

#include "stats.h"
#include <iostream>

int main(){
  stats::getInput(std::cin);
}

Like I said, I am a beginner in c++ so the answer is probably fairly simple, but c++ is vastly different than Python. I have seen similar questions, but none of them have helped me figure it out.

Thanks

Solution

The error message from the compiler is very clear.

getInput is a non-static member function of the class.

You need an object of the class to be able to use that member function.

Instead of

stats::getInput(std::cin);

use

stats obj;
obj.getInput(std::cin);

---

Another solution.

Since the class does not have any member variables, you may change getInput to a static member functions.

class stats {

   public:
      stats();
      static std::vector <double> getInput(std::istream& input_stream);

   private:
};

If you do that, you may use:

stats::getInput(std::cin);

---

Also, your loop to read the data can be simplified to:

while (input_stream >> x){
  stream.push_back(x);
}