Find number of items in .txt file

Question

I'm looking for a way to find the number of items in a .txt file.

The file structure is as follows:

students.txt pricem 1441912123
house.pdf jatkins 1442000124
users.txt kevin_tomlinson 1442001032
accounts.mdb kevin_tomlinson 1442210121
vacation.jpg smitty83 1442300125
calendar.cpp burtons 1442588012

The result should be 18 in this example since there are 18 separate "words" in this file.

I need that value so I can iterate through the items and assign them to an array of structures (maybe there's a way to accomplish both of these steps together?):

// my structure
struct AccessRecord
{
   string filename;
   string username;
   long timestamp;
};

// new instance of AccessRecord
// max possible records: 500
AccessRecord logRecords[500];

// while file has content
while (!fin.eof())
{
   // loop through file until end
   // max possible records: 500
   for (int i = 0; i < 500; i++) // need to figure out how to iterate
   {
      fin >> logRecords[i].filename
          >> logRecords[i].username
          >> logRecords[i].timestamp;
   }
}

Which will then be written to the screen.

So the question is, how do I find the count? Or is there a better way?

Recommended reading: [Why is iostream::eof inside a loop condition considered wrong?](https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong) — user4581301, May 04 '18 at 18:32

scohe001 · Answer 1 · 2018-05-04T18:09:19.017

2

You know that each line contains a string, a string and a long, so you can iterate with:

std::vector<AccessRecord> logs;
std::string fname, uname;
long tstamp;
while(fin >> fname >> uname >> tstamp) {
    logs.push_back(AccessRecord(fname, uname, tstamp));
    //To avoid copies, use: (thanks @Rakete1111!)
    //logs.emplace_back(std::move(fname), std::move(uname), tstamp);
}

This is assuming you've created a constructor for your struct like:

AccessRecord(std::string f, std::string u, long t)
               : filename(f), username(u), timestamp(t) { }

Notice that I'm using an std::vector here instead of an array so that we don't even have to worry about the number of items, since the vector will resize itself dynamically!

edited May 04 '18 at 18:09

answered May 04 '18 at 18:02

scohe001

13,879
2
28
47

You can remove that `new_log` by using `emplace_back`: `logs.emplace_back(std::move(fname), std::move(uname), tstamp);` + moves to avoid copies :) – Rakete1111 May 04 '18 at 18:04
Thanks, @scohe001. This is for school. We haven't learned about constructors or vectors yet. I think it might raise some eyebrows if I used this approach, not that I understand it anyway :) – Scott May 04 '18 at 18:06
@Rakete1111 not too familiar with `emplace_back` so I've left it as a comment. Thanks for the suggestion! – scohe001 May 04 '18 at 18:07
@scohe001 Well then you should get familiar with it :) It's really great :D – Rakete1111 May 04 '18 at 18:08
Yeah. Definitely will. I think those concepts are coming up in later chapters. – Scott May 04 '18 at 18:23

score 0 · Answer 2 · answered May 04 '18 at 21:30

You should overload operator>> for your structure:

struct AccessRecord
{
   string filename;
   string username;
   long timestamp;
   friend std::istream& operator>>(std::istream& input, AccessRecord& ar);
};

std::istream& operator>>(std::istream& input, AccessRecord& ar)
{
   input >> ar.filename;
   input >> ar.username;
   input >> ar.timestamp;
   return input;
}

This allows you to simplify your input function:

AccessRecord ar;
std::vector<AccessRecord> logs;
//...
while (fin >> ar)
{
  database.push_back(ar);
}

Usually, if you are accessing an objects data members directly outside of the class or structure, something is wrong. Search the internet for "data hiding", "c++ encapsulation" and "c++ loose coupling".

Find number of items in .txt file

2 Answers2