Reading table from txt file.

[johny15]

Hello.
I need help guys. I've txt file with data like this :
22 55 23
11 53 21
44 12 23
12 33 23
14 45 12

and i need to put in 2D array with size [2][4]. How can i do it ?

   ifstream myReadFile;
   myReadFile.open("filename.txt");
   int array[2][4];
 if(myReadFile)
{
  2x for here but how ?
}

So this code reads from file, but how i Can put all data in array?

[Ganado]

size [2][4] array is 8 entries, not large enough to fit your 15 entries.
I'm sure you meant size [3][5], but regardless,
you'd do something like:

int array[3][5];
for (int i = 0; i < 3; i++)
{
    for (int j = 0; j < 5; j++)
    {
        int n;
        file >> n;
        array[i][j] = n;
    }
}

[jonnin]

you can't.
math being what it is, 2*4 is 8, and your file appears to have much more than 8 numbers.

say the file actually had 8 values, though, or the first 8 were what belonged in the array in the right order. Because you used a solid block 2d array, you can collapse it to one-d and do it with simple code.
int *ip = &array[0][0];
for(int i = 0; i < 8; i++) //8 is 2*4;
{
filevar>>ip[i];

}

if you need a flexible sized 2-d construct, you need to re-do with vectors. Vectors do not collapse this way, you can either make a 1-d and fake the 2-d access or you have to double loop and deal with the problems caused by multi dimensions.

[Duthomhas]

// Read a table into a vector of vector
// • All elements are the same type
// • Elements are separated by spaces
// • No element is missing/empty

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

template <typename T>
std::vector <std::vector <T>>
read_table_of( std::istream& ins )
{
  std::vector <std::vector <T>> result;
  std::string s;
  while (getline( ins, s ))
  {
    std::vector <T> row;
    std::istringstream ss( s );
    T value;
    while (ss >> value) row.emplace_back( value );
    result.emplace_back( row );
  }
  return result;
}

// A simple example to run

#include <sstream>
#include <utility>

int main()
{
  std::istringstream input(
    "1 2 3\n"
    "4 5 6\n"
    "7 8 9\n"
  );

  auto table = read_table_of <int> ( input );
  
  for (auto record : table)
  { 
    for (auto field : record)
      std::cout << field << " ";
    std::cout << "\n";
  }
}

If you are stuck using arrays, let us know.

[johny15]

Ok, i have something like this :

int array[3][5];
for (int i = 0; i < 3; i++)
{
    for (int j = 0; j < 5; j++)
    {
        int n;
        file >> n;
        array[i][j] = n;
    }
}

its working properly, but what if my data in file looks like this:
122,754,897,154,
643,123,231,351,

numbers are separated by coma, how i can put each number in 2D array[2][4]?

[Ganado]

Look into std::getline.
http://www.cplusplus.com/reference/string/string/getline/

(1) istream& getline (istream& is, string& str, char delim);

Use ',' (comma) as the delimiter and experiment with that.

If you use this method, however, each result will be a string, and you'll have to convert the string into an int. (std::stoi can do this).
http://www.cplusplus.com/reference/string/stoi/

[dutch]

A simple but less robust solution for dealing with the commas:

const int Rows = 2, Cols = 4;
int a[Rows][Cols];

for (int row = 0; row < Rows; ++row)
{
    for (int col = 0; col < Cols; ++col)
    {
        int n;
        char ch;
        file >> n >> ch;
        a[row][col] = n;
    }
}

[Ganado]

Honestly that's much simpler and probably just as robust.
Only using getline means extra logic needed to remove the newlines as well.

[dutch]

It depends on his exact input. He shows a comma at the end of the line as well as between values. If that last comma isn't there, then the above simple solution will "eat" the first digit of the first number on the next line.

Some combination of our two approaches might be best. And combining with Duthomhas's approach allows any number of lines and even different numbers of values-per-line.

#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <vector>
#include <string>

using Table = std::vector<std::vector<int>>;

Table read_table(const std::string& filename) {
    Table table;
    std::ifstream in(filename);
    for (std::string line; std::getline(in, line); ) {
        if (line.find_first_not_of(" \t") == line.npos)
            continue; // skip blank lines
        table.resize(table.size() + 1);
        std::istringstream iss(line);
        for (int n; iss >> n; ) {
            table.back().push_back(n);
            char ch;
            iss >> ch; // eat comma (if not present at end of line, iss enters failed state)
        }
    }
    return table;
}

void print_table(const Table& table) {
    for (const auto& row: table) {
        for (int n: row)
            std::cout << std::setw(4) << n << ' ';
        std::cout << '\n';
    }
}

int main() {
    Table table = read_table("input_file");
    print_table(table);
}

[againtry]

ts working properly, but what if my data in file looks like this:
122,754,897,154,
643,123,231,351,

numbers are separated by coma, how i can put each number in 2D array[2][4]?

You have 2 rows of data with 4 pairs of a number followed by a comma.

End of story?