how to read from text file and store in matrix in c

Question

the first to say is that I'm totally new to coding, so plz forgive my mistakes. I'm now trying to read from a txt file which is rather large, it has about 1000000 lines and 4 cols

56.154 59.365 98.3333 20.11125
98.54 69.3645 52.3333 69.876
76.154 29.365 34.3333 75.114
37.154 57.365 7.0 24.768
........
........

I want to read them all and store them into a matrix, here is my code:

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>

int main()
{
  int i;
  int j;

/*matrix*/
int** mat=malloc(1000000*sizeof(int));
for(i=0;i<1000000;++i)
mat[i]=malloc(4*sizeof(int));


  FILE *file;
  file=fopen("12345.txt", "r");

 for(i = 0; i < 1000; i++)
  {
      for(j = 0; j < 4; j++) 
      {
       if (!fscanf(file, " %c", &mat[i][j])) 
           break;
       mat[i][j] -= '0'; /* I found it from internet but it doesn't work*/
       printf("\n",mat[i][j]);
      }

  }
  fclose(file);
}

The result is that I got nothing in my matrix. I hope u can help. Thanks in advance for any help.

---

Answer 1

Many Issues, consider following, and of course see comments

int main()
{
  int i;
  int j;

/*matrix*/
/*Use double , you have floating numbers not int*/

double** mat=malloc(1000000*sizeof(double*)); 
for(i=0;i<1000000;++i)
mat[i]=malloc(4*sizeof(double));


  FILE *file;
  file=fopen("1234.txt", "r");

 for(i = 0; i < 1000; i++)
  {
      for(j = 0; j < 4; j++) 
      {
  //Use lf format specifier, %c is for character
       if (!fscanf(file, "%lf", &mat[i][j])) 
           break;
      // mat[i][j] -= '0'; 
       printf("%lf\n",mat[i][j]); //Use lf format specifier, \n is for new line
      }

  }
  fclose(file);
}

Answer 2

You have a couple of things wrong with your code here.

First off you create a matrix of int yet you are reading in float values it looks like. You probably want to use double

Second, when you are reading a double you should use

fscanf(file, "%lf", &some_double);  // fscanf(file, "%d", &some_int); for integers

Also when you are allocating your matrix, your first malloc you should pass

sizeof(double *) // or int * if you are really trying to use integers

Finally your line that does:

mat[i][j] -= '0'

What are you trying to accomplish here? You're taking the int that you (tried) to read in and subtracting off '0'...

Edit I also notice that you are hard coding the number of lines you are reading, I wouldn't do that unless you know the format of the file.

Answer 3

1. fscanf( "%c", ... ) only scans one single character (eg '5'). By subtracting '0' you get the integer value 5 from the character '5' . You can use "%d" to scan integers that consist only of digits (not including formatting characters), or "%f" for floats (not sure if 56.154 is to be read as "56 thousand 154" (continental europe) or "56 plus 154/1000" (GB / USA) (the rest of the world: don't be offended I just don't know)

2. printf( "\\n", ... ) : you forgot to use any formatting string such as %d (int), %f (float) ... So your parameter will not be printed, just the newline itself.

3. int** mat=malloc(1000000*sizeof(int)); You're allocating an array of int * here, so it should be int** mat=malloc(1000000*sizeof(int *));

Edit: I've looked again at your text file and have seen numbers like 98.54 that can't be formatted integers. So it's quite clear you will need float or double instead if int for your array and use "%f" for float or "%lf" for double in both fscanf() and printf()