Reading / input column of numbers into an array

Hello all.

I have a text file with one column of numbers (vector) e.g.:

1
2
3
4
5
6

They are separated by a return.

As I'm fairly new to C I thought I would check out my logic with you before I start writing the code. So the sequence of events to read in a vector should be:

1. Use fopen and the read option to get the file open.
2. Use scanf to make a string containing the contence of a line. It will know when to stop when it finds \n.
3. Convert the string of charaters in 2. into a number.
4. Put the number into an elemet of an array
5. Loop 2. -> 4. until EOF is returned
4. fclose
5. return number array.

If you have experience with this kind of thing, how does that sound? Any advice?

Cheers, Daniel.

Quote:

---

Originally Posted by boyfarrell

2. Use scanf to make a string containing the contence of a line. It will know when to stop when it finds \n.
3. Convert the string of charaters in 2. into a number.
4. Put the number into an elemet of an array
5. Loop 2. -> 4. until EOF is returned

---

I might use fscanf to read and convert until it fails, putting a successfully converted value directly into the array.

Code:

---

#include <stdio.h>

size_t foo(const char *filename, int *array, size_t size)
{
  size_t count = 0;
  FILE *file = fopen(filename, "r");
  if ( file )
  {
      int *end = array + size;
      while ( fscanf(file, "%d", array) == 1 )
      {
        if ( ++array >= end )
        {
            puts("too many inputs");
            break;
        }
        ++count;
      }
      fclose(file);
  }
  else
  {
      perror(filename);
  }
  return count;
}

int main()
{
  int array[10];
  size_t i, count = foo("file.txt", array, sizeof array / sizeof *array);
  for ( i = 0; i < count; ++i )
  {
      printf("array[%lu] = %d\n", (long unsigned)i, array[i]);
  }
  return 0;
}

/* my output
array[0] = 1
array[1] = 2
array[2] = 3
array[3] = 4
array[4] = 5
array[5] = 6
*/

---

Hey thanks so much for the code! It works a perfectly.

I will expand it to be able to read in files that have more than one column, i.e. separated my a tab or a space etc. So , don't post any code I want to do this my self!!! :D. Will post up when I'm finished.

Daniel.

PS - by the way where did you get that code from, you had it lying around or pulled it off the net? Thanks again.

Dave's a good programmer, so he probably made it up. He's helped me too.

mw

Think I will be very easy to make fscanf read a file with 2 columns. You just need to change the 'format' (i.e. second input of fscanf) to \f\t\f\n. This would expect a float, a tab, another float and then a new line.

I forgot to mention. I'm having some trouble making this code accept doubles? I have changed it a few things around:

Code:

---

#include <stdio.h>

int foo(const char *filename, double *array, int size)
{
  int count = 0;
  FILE *file = fopen(filename, "r");
  if ( file )
  {
      double *end = array + size;
      while ( fscanf(file, "%f", array) == 1 )
      {
        if ( ++array >= end )
        {
            puts("too many inputs");
            break;
        }
        ++count;
      }
      fclose(file);
  }
  else
  {
      perror(filename);
  }
  return count;
}

int main()
{
  double array[10];
  int i, count;
  count = foo("test1.txt", array, sizeof array / sizeof *array);
  for ( i = 0; i < count; ++i )
  {
      printf("array[%i] = %d\n", (int)i, array[i]);
  }
  return 0;
}

---

This builds with out any error, but returns junk! Have a look:

Code:

---

array[0] = 1065353216
array[1] = 1073741824
array[2] = 1079613850
array[3] = 1085485875
array[4] = 1091148186
array[5] = 1092301619

---

I have changed size_t because I don't really understand it. But I figure the output of 'foo' will always be an int. Also, the input will always be a double. Can anybody see the problem? (I have of course changed the input file to contain numbers that have a decimal point):
1.0
2.0
3.4
5.6
8.6
9.7

Sorry about this guys but the printf should read

Code:

---

printf("array[%i] = %f\n", (int)i, array[i]);

---

This also changes the output as would be expected. However, it's still not what's in the file!

> while ( fscanf(file, "%f", array) == 1 )
The conversion for a double is "%lf"

If you're using gcc as your compiler, use the
-W -Wall
options as well.

You legend!

Thanks so much, works perfectly now.

Cheers, Daniel. ;)