This is the code which put an extra line to the std::string array. I am here trying to print last k lines of file. Any help is appreciated.

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

//file.exceptions(ifstream::eofbit | ifstream::failbit | ifstream::badbit);
void print_last(unsigned k, string file_name)
{
    string *data=new string[k];
    unsigned last=0;
    ifstream is;
    is.open(file_name.c_str(), ios::binary);
    if(is.is_open())
    {
        while(getline(is, data[last]))  //while (getline( myfile, line ))  // same as: while (getline( myfile, line ).good())
        {
            last=(last+1)%k;
        }
        is.close();
        for(int i=0;i<k;i++)
        {
            last=(last+1)%k;
            cout<<data[last]<<endl;
        }
    }

}

int main()
{
    unsigned k;
    string file_name;
    cin>>k>>file_name;
    print_last(k, file_name);
}

Check your text file -- your program ran ok for me. I have a text file that lists US state names and their abbreviations. Ran your program with "5 states.txt" and it printed the last 5 lines of that file. If the text file contains blank lines at the beginning or end of the file your program may not produce the desired results unless you expect the blank lines.

What problem are you having such that you need help? Simply saying "Any help is appreciated" is very broad. For example, I'd do something completely different; does throwing away your code and starting over constitute "help"?

It seems strange but on my console it is showing only last four lines plus an extra empty line. Moreover, I have tested it with three files.

What problem are you having such that you need help?
It is actually storing an extra empty empty string to the data array but I intend to print last 5 human readable lines of a file.

It is actually storing an extra empty string in the data array but I intend to print last 5 human readable lines of a file.

You can change your program to ignore empty lines, just add the check just before line 17. If the line is empty don't increment the counter. But that may cause other undesireable side affects. Your program runs correctly as it is, if it doesn't display the lines you think it should then you need to edit the text file and remove the blank lines.

Edited 3 Years Ago by Ancient Dragon

I was updating the std::string data array even at the end of file which was owverwriting the oldest line stored in k sized array. I have changed it to use an intermediate string instead and is working fine with this modification.

void print_last(unsigned k, string file_name)
{
    string *data=new string[k];
    string str;
    unsigned last=0;
    ifstream is;
    is.open(file_name.c_str(), ios::binary);
    if(is.is_open())
    {
        while(getline(is, str)) //while (getline( myfile, line ))  // same as: while (getline( myfile, line ).good())
        {
            data[last]=str;
            last=(last+1)%k;
        }
        is.close();
        for(int i=0;i<k;i++)
        {
            cout<<data[last]<<endl;
            last=(last+1)%k;
        }
    }
    delete[] data;

}
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