How to read in a set of values from a text file, then go to the next line and do the same

Question

Im trying to read a list like this one

James  John 15 5 1
Douglas Frank 23 8 1
Bnejamin Zach 17 1 4

and store each value into a a separate variable. The names are strings, and the other numbers are floats and an int. I can get the data from one line so far, but I dont know how to go onto the next line and do the same. Here is my code so far.

#include <iostream>
#include <string>
#include <fstream>


using namespace std;

int main()
{
ifstream employees;
string lastname, firstname, lastname1, firstname1, lastname2, firstname2;
float base, sales, base1, sales1, base2, sales2;
int years, years1, years2;


employees.open("employees.txt");

while (employees)

  {
employees >> lastname >> firstname >> base >> sales >> years;

I want to keep it as simple as possible, I dont know user defined functions, arrays, or vectors at all yet. So is there a simple function that will just end the line at years; and go to the next line and carry on?

Thanks.

Answer 1

Opening and reading a file properly is harder than learning what an array is. If you don't use an array you have to use too many variables to hold all your data, and you have to repeatedly write the code to read from the file, rather than writing it once in a loop.

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

int main()
{

    string firstNames[3];
    string lastNames[3];
    float heights[3];
    float weights[3];
    int ages[3];

    ifstream infile("data.txt");

    if(!infile)
    {
        cout << "Couldn't open file!" << endl;
        return 1;
    }

    int count = 0;

    while (infile >> firstNames[count] 
                  >> lastNames[count]
                  >> heights[count] 
                  >> weights[count] 
                  >> ages[count] ) 
    {

        ++count;
    }


    infile.close();

    for (int i = 0; i<count; ++i) {
        cout << firstNames[i] << " " 
             << lastNames[i] << " " 
             << heights[i] << " "
             << weights[i] << " "
             << ages[i] << " " << endl;
    }


    return 0;
}


--output:--
James John 15 5 1 
Douglas Frank 23 8 1 
Bnejamin Zach 17 1 4 

Compare to this disaster:

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

int main()
{

    string firstName0,firstName1, firstName2;
    string lastName0, lastName1, lastName2;
    float height0, height1, height2;
    float weight0, weight1, weight2;
    int age0, age1, age2;

    ifstream infile("data.txt");

    if(!infile)
    {
        cout << "Couldn't open file!" << endl;
        return 1;
    }

    infile >> firstName0 >> lastName0 >> height0 >> weight0 >> age0;
    infile >> firstName1 >> lastName1 >> height1 >> weight1 >> age1;
    infile >> firstName2 >> lastName2 >> height2 >> weight2 >> age2;


    infile.close();

    cout << firstName0 << " "
         << lastName0 << " "
         << height0 << " "
         << weight0 << " "
         << age0 << endl;

    cout << firstName1 << " "
         << lastName1 << " "
         << height1 << " "
         << weight1 << " "
         << age1 << endl;

    cout << firstName2 << " "
         << lastName2 << " "
         << height2 << " "
         << weight2 << " "
         << age2 << endl;

    return 0;
}

--output:--
James John 15 5 1
Douglas Frank 23 8 1
Bnejamin Zach 17 1 4

Look at all the code you have to repeat.

Note that when you use an array, the variable names become firstNames[0] (v. firstName0), lastNames[0] (v. lastName0), etc., and firstNames[1] (v. firstName1) and lastNames[1] (v. lastName0).

Answer 2

There are many ways in C++ to accomplish what you are trying to do. One approach that allows for data validation is to use the std::getline function to read the file one line at a time and then use a std::stringstream to parse the data.. This allows you to validate the data and continue processing if the data on a line is malformed.

[As Mats noted you can use a data structure and std::vector to make storing and managing the data easier.]

#include <fstream>
#include <sstream>
#include <string>
#include <vector>


struct employee
{
    std::string firstname;
    std::string lastname;
    float base;
    float sales;
    int years;
};

int main()
{

    std::ifstream employeeFile;
    employeeFile.open("employees.txt");

    std::string tmpLine;
    std::vector<employee> employeeTable;

    // read in an entire line at a time 
    while(std::getline(employeeFile, tmpLine))
    {
        // Place the input line into a stream that reads from
        // a string instead of a file.
        std::stringstream inputLine(tmpLine);


        // Try parsing the data. The ! operator is used here to check
        // for errors. Since we expect the data to be in a specific format
        // we want to be able to handle situations where the input line
        // may be malformed. For example, encountering a string where
        // a number should be.
        employee e;
        if(!(inputLine >> e.firstname >> e.lastname >> e.base >> e.sales >> e.years))
        {
            // ... error parsing input. Report the error
            // or handle it in some other way.

            continue;   // keep going!
        }

        // Add to the vector
        employeeTable.push_back(e);
    }

    return 0;
}

Answer 3

You can use getline inside your loop to retrieve each line and then use it with a stringstream

Something like:

string line;
while(getline(employees,line))
{
  //doSomething
}

If you can't use arrays to store them easily, you can put a counter to know at which line you're at, but this is very repetitive, and the number of lines in your file cannot vary:

string line;
for (int count = 1 ; count <= 3 ; count++)
{
  getline(employees,line);
  istringstream iss(line);
  if (count == 1)
  {
    iss >> lastname >> firstname >> base >> sales >> years;
  }
  else if (count == 2)
  {
    iss >> lastname1 >> firstname1 >> base1 >> sales1 >> years1;
  }
  else if (count == 3)
  {
    iss >> lastname2 >> firstname2 >> base2 >> sales2 >> years2;
  }
}

Answer 4

Use an array. Whenever you end up with "I want to add a number to this variable because I want more than one", if the number reaches more than 2, then you should really use an array (unless very special cases).

You may also want to use a struct to store your different values (firstname, lastname, base, sales and years) - that way, you only get a single array, rather than several different arrays.

Since this is C++, arrays means vector. In other words:

struct employee
{
    string firstname, lastname;
    float base, sales;
    int years;
};


vector<employee> emp_table;

employee e;

while (employees >> e.firstname >> e.lastname >> e.base >> e.sales >> e.years)
{
    emp_table.push_back(e); 
}

Note I put the input of employees as the while-condition. This avoids an extra loop iteration and "pushing back" a second copy of the last entry when you have reached end of file.