Reading from TextFile in C++

Question

I am a java/C# developer and i am trying to write a C or C++ code to read data from a text file. this is very easily done in java and c# but not in c or c++.

the textfile i am reading looks like this:

a,b,c,d,e
1,0,1,1,0
0,1,1,0,0
0,0,0,1,1

i need to store the values in 2 arrays.
the 1st one is a 1D char array which will contain: a b c d e
the 2nd one is a 2D bool array which will contain:

  1 0 1 1 0
  0 1 1 0 0
  0 0 0 1 1

how can i do this?

[This question](http://stackoverflow.com/questions/415515/) may contain some useful information. — Björn Pollex, Mar 15 '11 at 13:39
C or C++? the answers are (I think), or at least can be, very very different. Also, the "a,b,c,d,e" in your example will always be made up of single characters (ie no "foo,bar,baz,qux,quux")? — pmg, Mar 15 '11 at 14:13
I would recommend storing inside a vector, it would give you a lot more flexibility if you want to switch it up later. — ultifinitus, Mar 15 '11 at 19:01

hiddensunset4 · Answer 1 · 2011-03-15T13:58:02.607

I suggest you at least make an attempt at what you are trying to do, to help you get started, here is a basic read out of the example data you provided. This example should be simple enough to allow you to expand it to meet other data sets.

#include <iostream>
#include <fstream>

int main() {
    const int n_letters = 5;

    const int n_columns = 5;
    const int n_rows = 3;

    char letters[n_letters];
    bool booleans[n_rows][n_columns];

    std::ifstream stream("myfile.txt");
    if (stream) {
        for (int i = 0; i < n_letters; ++i) {
            stream >> letters[i];
            std::cout << letters[i] << ',';
        }
        std::cout << '\n';
        for (int i = 0; i < n_rows; ++i) {
            for (int j = 0; j < n_columns; ++j) {
                stream >> booleans[i][j];
                std::cout << booleans[i][j] << ',';
            }
            std::cout << '\n';
        }
    }
    return 0;
}

Reads the following text:

And outputs:

a,b,c,d,e
1,0,1,1,0
0,1,1,0,0
0,0,0,1,1

you should use a two dimensional array for numbers, since that's what the op asked for(2D == two dimensions). — Shinnok, Mar 15 '11 at 13:52

score 0 · Answer 2 · answered Mar 15 '11 at 18:48

A first comment: when parsing a file, it's often useful to read the file line by line, and then parse each line, using std::istringstream, or boost::regex, or whatever other technique you please. I like boost::regex, because it immediately indicates if there is a syntax error, but carefully designed, istream can as well.

The first thing, in any case, is to specify more precisely the formats: Is there always just one letter? Are the numbers always Just 0 and 1? Are there always exactly five values per line? Until we know that, it's rather difficult to say more.

Reading from TextFile in C++

2 Answers2