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

Here is a pretty clean approach that uses boost::tokenizer. This returns an object providing begin() and end() member functions; for a complete interface, see the documentation of the tokenizer class.

#include 
#include 
#include  


using istream_tokenizer = boost::tokenizer,
                                           std::istreambuf_iterator>;

istream_tokenizer line_range(std::istream& is);
{
    using separator = boost::char_separator;

    return istream_tokenizer{std::istreambuf_iterator{is},
                             std::istreambuf_iterator{},
                             separator{"\n", "", boost::keep_empty_tokens}};
}

This hardcodes char as the stream's character type, but this could be templatized.

The function can be used as follows:

#include 

std::istringstream is{"A\nBB\n\nCCC"};

auto lines = line_range(is);
std::vector line_vec{lines.begin(), lines.end()};
assert(line_vec == (std::vector{{"A", "BB", "", "CCC"}}));

Naturally, it can also be used with an std::ifstream created by opening a file:

std::ifstream ifs{"filename.txt"};
auto lines = line_range(ifs);