How to check if there is a new line or not at the end of ifstream file. (c++)

Question

I have a program that works perfectly if there is a \\n at the end of ifstream file.

The task was like this: Define the structure of the product ( product name , category , price , quantity in stock ) . From File trgovina.txt ( It may already contain predefined products. "Like in the picture i posted) Through functions :

1. 1 load the products in to array from an existing file tgovina.txt
2. 2 Allow the product name printing from the file proizvodi.txt ( every product in new line )
3. enable search of products by category ( load the category from the user and prints out the names of products and categories on the screen and into the file which is named as "the required category" )
4. Enable printing of product which are less than 10 in stock in the file lessthen10.txt
5. Allow printing the most expensive and the cheapest products on display
6. Allow the entry of new products into the database ( write it to a file trgovina.txt )

The problem starts here : if the person stops writing at the first yellow marker, I would like to add a new line, so that when I want to add a new text, it will start in new line. If there is already a new line at the end of the text file, I want to just continue writing without adding new line.

The second problem is if the ofstream file has no text: in that case, I don't want to add a new line.

ofstream dat("trgovina.txt", std::ios_base::app);
if (!dat)
{
  cout << "Mistake!" << endl;
  return;
}
string name;
string category;
bool a = true;
double price;
int quantity;
while (a)
{   
  **//Here I want to check if there is a "\n" sign at the end of text
    //if there isn't I want to add one, and then continue writing.
    // But if the text file was empty i dont want to add new line**

  cout << "enter the name of new product: ";
  getline(cin, name);
  dat << name << "|";
  cout << "enter the category of new product: ";
  getline(cin, category);
  dat << category << "|";
  cout << "enter the price of new product: ";
  cin >> price;
  dat << price << "|";
  cout << "enter the quantity of new product: ";
  cin >> quantity;
  dat << quantity << endl; **//This works if the txt file is empty or if 
                             //there is "\n" at the end**
  cout << "more? (1 / 0)";
  cin >> a;
  cin.ignore();
  system("cls");
};
dat.close();

Sorry for my bad english.

I got an error using

while (a)
{   
    trgovina.seekg(-1); 
    char c;
    trgovina.get(c);
    if (c == '\n')
    {

    }
    else
    {
        dat << endl;
    }

This is the picture of the txt file after running few new lines from this code. It put's a new line on the top if the file was empty, if not it works good.

Answer 1

Its an ofstream so a stream in which you can only write. What you need is both reading (to determine what's inside) and write (to add items), this is called an fstream . You can read, write and seek into a fstream . To determine if the last char of it is a newline, just seek to the last char and read it with something like that:

fstream f("myfile.txt",std::fstream::in | std::fstream::out);
f.seekg(-1,is.f.end); // move the the end
char c;
f.get(c);
if (c=='\n') ...
else         ...