How to test if a line is empty?

I'm actually trying to understand how does the getline() function works! But I'm facing difficulties to test if a line is empty or not!

Here is my code:

ifstream fichier("upload.txt",ios::binary);
string ligne;
while(getline(fichier,ligne))
{
    cout<<ligne<<endl;
    if(ligne=="")
         cout<<"line below is empty"<<endl;         
}

But, the if-condition seems to be not working :((

On Windows, a line break is normally CRLF (0x0D 0x0A). std::getline() will read until it encounters the LF and discard it from the returned std::string. If the std::ifstream is opened in text mode (the default mode), platform line breaks are normalized to LF and a leading CR will also be discarded. But, if opened in binary mode, the CR will not be discarded. So you will have to check for that:

ifstream fichier("upload.txt", ios::binary);
string ligne;
while (getline(fichier, ligne)) {
	if (ligne.empty() || ligne == "\r") {
		cout << "line is empty" << endl;
	} else {
		cout << ligne << endl;
	}
}

Otherwise, don't use binary mode for text files:

ifstream fichier("upload.txt");
string ligne;
while (getline(fichier, ligne)) {
	if (ligne.empty()) {
		cout << "line is empty" << endl;
	} else {
		cout << ligne << endl;
	}
}

Your problem is opening file in binary. Other than that, you should do few things :

1. Check if file is properly opened

2. Compare against empty()

3. Check if string only contains space , then it's considered empty.

4. Close file

   ifstream fichier("upload.txt", std::ifstream::in ); //File opened for reading.
   string ligne;
   //Always Check if file is properly opened.
   if (fichier.is_open() ) 
   {
      while(getline(fichier,ligne))
      {
         cout<<ligne<<endl;
          if(ligne.empty() || str.find_first_not_of(' ') == std::string::npos)
           cout<<"line below is empty"<<endl;         
      }
      fichier.close();
   
   }
   else 
   {
    // show message:
     std::cout << "Error opening file";
   }