I want to save some data as a text file, the first txt file will contain header information, the other text file will save data streamed from sensors, so with the help from the internet I created the following "datalogger.cpp" file

Qt Code: 
  1. #include "datalogger.h"
  2. #include <QDebug>
  3. #include <iostream>
  4. #include <QFile>
  5.  
  6. DataLogger::DataLogger(QObject *parent) : QObject(parent)
  7.    {
  8.  
  9.     }
  10.  
  11.    DataLogger::~DataLogger(){
  12.  
  13.     }
  14.     void DataLogger::save(DataStream &input){
  15.         saveAsText(input);
  16.  
  17.  
  18.     }
  19.     void DataLogger::saveAsText(DataStream &input){
  20.  
  21.                         QTextStream outHeader(&outFileHeader);
  22.  
  23.                         outHeader   << "[CAPTURE SETTINGS]\n"
  24.                                     << "Filename: " <<      SettingsSingleton::instance().getFileName() << ".txt \n"
  25.                                     << "Samples: " <<       QString::number(input.size()) << "\n"
  26.                                     << "Duration: " <<      QString::number(input.back().time) << "ms \n"
  27.                                     << "Sample rate: " <<   QString::number(SettingsSingleton::instance().getSampleRate()) << " Hz\n"
  28.                                     << "Source: "  <<       SettingsSingleton::instance().getSource() << "\n"                                  
  29.  
  30.                         outFileHeader.close();
  31.  
  32.                     }
  33.  
  34.                     QFile outFile(SettingsSingleton::instance().getFileName() + ".txt");
  35.  
  36.                      QTextStream out(&outFile);                      
  37.  
  38.                         for (int i ; i<input.size();i++){
  39.                                const EcgStreamObject tmp=input.at(i);
  40.                                                 out << tmp.toText() << endl; //"\n";    
  41.  
  42.                         }  
  43.  
  44.                         outFile.close();
  45.                     }    
  46.  
  47.     }
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I have my "DataStream" input variable that I want to pass to the method and save as a ".txt" file, however I do no know how to call the method "void DataLogger::save(DataStream &input)" from a different ".cpp" file where the DataStream variable is located.
I am extremely new to c++ please it as simple as possible please.
Thank you in advance