C++ read txt data and char into 2D array

Question

I would like to read text into arrayA[][] which includes data and characters. It seems like

And I need to calculate the data then. My code cannot do that. I try to output A[][] to see if there is anything wrong and it turns out that all the elements are 0.000. Please help me to find out how to change it. Thanks!

enter code here

#define _CRT_SECURE_NO_DEPRECATE
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <string>
#include <fstream>
#include <limits>
int    p = 518868;
int    q = 11;
int    s, t, i, j, k, m, d, r, u;
double A[518868][11];
int    main(void)
{

    FILE  *fid;

    using namespace std;

    ifstream file("dump600.txt");

    if (file.is_open())
      {
        for (i = 1; i <= p; i++)
          {
            for (j = 1; j <= q; j++)
              {
                file >> A[i][j];
              }
          }
      }



fid = fopen("RstA600.txt", "wt");
for (i = 1; i <= 10000; i++)
{
    for (j = 1; j <= 11; j++)
    {
        if (j == 11)
        {
           fprintf(fid, "%f\n", A[i][j]);
        }
        else
        {
            fprintf(fid, "%f\t", A[i][j]);
        }
    }
}
fclose(fid);

dump600.txt
id  type x  y   z   c_q[1]       c_q[2]     c_q[3]       c_q[4]    x    y
1   1    0  0   30  -0.0075608  -0.710037   0.703789    0.021699    0   0
3   1    10 0   30  0.0138984   -0.409617   0.0338428   -0.911523   10  0
5   1    20 0   30  -0.31169    -0.685503   0.450455    0.479609    20  0
7   1    30 0   30  -0.194787   -0.373789   0.511419    -0.74886    30  0

Arrays in C++ start with index 0, not 1, so it should be for (i = 0; i < p; i++) and so on; further, check the return value of operator >> to see if a value could have been read correctly. Your code may fail if the first line contains anything else than a number, because it will then repeatedly failing in reading this non-number as a number. — Stephan Lechner
– Stephan Lechner, Commented Aug 7, 2017 at 20:28
can you please format this to something readable It seems like id type x y z c_q[1] c_q[2] c_q[3] c_q[4] x y 1 1 0 0 30 -0.0075608 -0.710037 0.703789 0.021699 0 0 3 1 10 0 30 0.0138984 -0.409617 0.0338428 -0.911523 10 0 5 1 20 0 30 -0.31169 -0.685503 0.450455 0.479609 20 0 7 1 30 0 30 -0.194787 -0.373789 0.511419 -0.74886 30 0 — Hariom Singh
– Hariom Singh, Commented Aug 7, 2017 at 20:29
This is a good opportunity to learn to use a debugger and step through your code, to find out what's gone wrong. — hnefatl
– hnefatl, Commented Aug 7, 2017 at 20:30
Read and discard the first line with std::getline. After that, use something similar to if (! file >> A[i][j]) { std::cerr << "cannot parse input\n"; return -1; } to read the file into the array. — user4581301
– user4581301, Commented Aug 7, 2017 at 20:54
@Ron vector of vectors is slow due to poor spatial locality. A vector of std::array would be better assuming (and it's a fairly safe assumption) that std::array doesn't do anything silly to ruin data contiguity. — user4581301
– user4581301, Commented Aug 7, 2017 at 20:59

Stephan Lechner · Accepted Answer · 2017-08-07 21:04:38Z

1

The problem seems to be the first line containing text, which will let any file >> A[i][j] fail. To overcome this, you could skip the first line using a std::getline; also consider to somehow react on invalid input. Further, indexes in C++ start with 0, not with 1, such that for (j = 1; j <= q; j++) and so on run out of bounds and yield undefined behaviour. See a sample of code that should work:

  if (file.is_open())
  {
    std::string line;
    if(std::getline(file, line)) {
      for (i = 0; i < p; i++)
      {
          for (j = 0; j < q; j++)
          {
             if (!file >> A[i][j]) {
                cout << "Invalid input.";
             }
          }
      }
    }
  }

edited Aug 7, 2017 at 21:04

answered Aug 7, 2017 at 21:00

Stephan Lechner

35.2k4 gold badges38 silver badges59 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

C++ read txt data and char into 2D array

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related