read irregular file into a 2-dimension array using C++

Question

I am very new to C++. I believe there are solutions already in stackoverflow but I cannot find any.

I need to read data from a txt file into a 2 dimension array. File is like

54 3 5 678

10 1 2 3 46 8 1 1 2 3 4

9 8 10

Each line contains up to 120 integers and there are no more than 60 lines.

Your reply is high appreciated. Thanks!

Update: It is not homework. Thank you all!

If this is homework, you should add the "homework" tag and briefly explain the requirements of the assignment. — Jon Purdy, Sep 24 '11 at 23:43

sehe · Answer 1 · 2011-09-25T18:59:13.243

Here goes...

Definitely the answer you need¹, though very correct and true to C++ nature.

Instead of parsing to a jagged array it reads into a vector of vectors of ints.
^{(Or, a list of sets, a stack of deques, whatever tickles your fancy).}

In absense of any specs, I accept

any number of lines (until the first empty one),
any number (>0) of numbers on any line
ignoring whitespace anywhere (besides the line ends)
any integer numbers (including negatives...)

Cheers

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/support_istream_iterator.hpp>
#include <boost/spirit/include/karma.hpp>

namespace spirit = boost::spirit;
namespace qi     = boost::spirit::qi;
namespace karma  = boost::spirit::karma;

int main()
{
    std::cin.unsetf(std::ios::skipws);
    spirit::istream_iterator b(std::cin), e;

    std::vector<std::vector<int> > vectors;

    if (qi::phrase_parse(b, e, +qi::int_ % qi::eol, qi::space - qi::eol, vectors))
        std::cout 
            << karma::format(karma::right_align(8)[karma::auto_] % ',' % '\n', vectors)
            << std::endl;

    return 0;
}

For the input shown, it prints:

  54,       3,       5,     678
  10,       1,       2,       3,      46,       8,       1,       1,       2,       3,       4
   9,       8,      10

Update Standard Library version

See it live here: http://ideone.com/HtAAg

For fun, here is the standard-library-only version of the same. Just to show, that things don't have to be all that bad when you go without the jet propulsion libraries :)

#include <vector>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <iterator>

static void display(const std::vector<int>& v)
{
    std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, ",\t"));
    std::cout << std::endl;
}

int main()
{
    std::vector<std::vector<int> > vectors;

    std::string s;
    while (std::getline(std::cin, s))
    {
        std::istringstream iss(s);
        vectors.push_back(std::vector<int>());
        std::copy(std::istream_iterator<int>(iss), std::istream_iterator<int>(), std::back_inserter(vectors.back()));
    }

    std::for_each(vectors.begin(), vectors.end(), display);
    return 0;
}

¹ I'm assuming that this is homework. I'm also assuming that your teacher wants you to allocate a int[120][60] or int[60][120] (how would you know how many numbers were read per line? - you'd need extra storage)

@kisplit: [`qi::int_` parses an integer](http://biweeyi.notlong.com), [`+qi::int_` parses 1 or more](http://qioperator.notlong.com) integers, `(lhs) `[`% qi::eol` expects one or more _lhs_ separated by newlines](http://qilist.notlong.com); [`qi::space - qi::eol` accepts any whitespace _except_ newlines](http://qidiff.notlong.com). All of this is part of the EDSL for grammars ([parser expressions](http://qiparsers.notlong.com)) as defined by Spirit (based on Boost Proto). — sehe, Sep 25 '11 at 12:33
@kisplit: just for fun added a 'standard library' version that does the same - without requiring boost. It compiles in a fraction of the time too :) See it live here: http://ideone.com/HtAAg — sehe, Sep 25 '11 at 19:01

score 0 · Accepted Answer · answered Sep 25 '11 at 03:42

My solution, just substitute cin with your file stream

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main(int argc, char* argv[]) {
    string line;
    int ints[60][120] = {0}, i = 0;
    stringstream ss;

    while (getline(cin, line)) {
        ss.str(line);

        for(int j = 0; j < 120 && ss; j++) {
            ss >> ints[i][j];
        }

        ss.clear();
        i++;
    }

    cin.ignore();
    return 0;
}

read irregular file into a 2-dimension array using C++

2 Answers2

Update Standard Library version

Linked