Is there a C++ iterator that can iterate over a file line by line?

Question

I would like to get an istream_iterator-style iterator that returns each line of the file as a string rather than each word. Is this possible?

Answer 1

The standard library does not provide iterators to do this (although you can implement something like that on your own), but you can simply use the getline function (not the istream method) to read a whole line from an input stream to a C++ string.

Example:

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

using namespace std;

int main()
{
    ifstream is;
    string str;
    is.open("test.txt");
    while(is)
    {
        getline(is, str);
        reverse(str.begin(), str.end());
        cout<<str.c_str()<<endl;
    }
    return 0;
}

Answer 2

EDIT: This same trick was already posted by someone else in a previous thread.

It is easy to have istream_iterator do what you want:

namespace detail 
{
    class Line : std::string 
    { 
        friend std::istream & operator>>(std::istream & is, Line & line)
        {   
            return std::getline(is, line);
        }
    };
}

template<class OutIt>
void read_lines(std::istream& is, OutIt dest)
{
    typedef std::istream_iterator<detail::Line> InIt;
    std::copy(InIt(is), InIt(), dest);
}

int main()
{
    std::vector<std::string> v;
    read_lines(std::cin, std::back_inserter(v));

    return 0;
}

Answer 3

You could write your own iterator. It's not that hard. An iterator is just a class on which (simply speaking) the increment and * operators are defined.

Look at http://www.drdobbs.com/cpp/184401417 to get started writing your own iterators.

Answer 4

You can use istreambuf_iterator instead of istream_iterator. It doesn't ignore control characters like istream_iterator.

code.cpp:

#include <iterator>
#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream file("input.txt");

    istreambuf_iterator<char> i_file(file);

    istreambuf_iterator<char> eof;

    std::string buffer;
    while(i_file != eof)
    {
        buffer += *i_file;
        if(*i_file == '\n')
        {
            std::cout << buffer;
            buffer.clear();
        }
        ++i_file;
    }

    return 0;
}

input.txt:

ahhhh test *<-- There is a line feed here*
bhhhh second test *<-- There is a line feed here*

output:

ahhhh test
bhhhh second test

Answer 5

Here is a solution. The exemple print the input file with @@ at the end of each line.

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

using namespace std;

class line : public string {};

std::istream &operator>>(std::istream &is, line &l)
{
    std::getline(is, l);
    return is;
}

int main()
{
    std::ifstream inputFile("input.txt");

    istream_iterator<line> begin(inputFile);
    istream_iterator<line> end;

    for(istream_iterator<line> it = begin; it != end; ++it)
    {
        cout << *it << "@@\n";
    }

    getchar();
}

Edit : Manuel has been faster.