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Re: Please help -- cannot read double data from file into array

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dakupoto@gmail.com writes:

> Could some C kanguage guru please help ?
> I am trying to read double data from a 
> simple text file into an array. The data 
> can be read in correctly, but I am unable 
> use the values read into the array, later.
>
> The input file looks like:
> 0       5.091259e-09    -2.16165e+01
> 1       5.213820e-09    -2.76803e+01
> 2       5.357648e-09    -2.74552e+01
> 3       5.524594e-09    -1.84046e+01
> 4       5.611980e-09    -1.15479e+01
> 5       5.693378e-09    -5.40278e+00
> 6       5.768690e-09    -1.01834e+00
> 7       5.847084e-09    1.373752e+00
> 8       5.910280e-09    1.400719e+00
> 9       5.978795e-09    -5.31898e-01
> 10      6.089210e-09    -7.05779e+00
> 11      6.204666e-09    -1.59755e+01
> 12      6.322522e-09    -2.39013e+01
> 13      6.456074e-09    -2.76082e+01
> 14      6.600659e-09    -2.36523e+01
> 15      6.719486e-09    -1.56844e+01
> 16      6.804431e-09    -8.88031e+00
> 17      6.883560e-09    -3.05696e+00
> 18      6.959700e-09    1.044230e+00
> 19      7.037793e-09    2.966563e+00
> ....
> ....
>
> Each double value in a line is separated
> by a tab(\t). The data is read in, line 
> line as a character string, and then each 
> string is parsed to red in the numerical 
> values. The data is stored in a 2 dimensional
> array:
>
> const unsigned int NUMROWS = 262144;
> const unsigned int PWROF2 = 18;
> char data[64];
> FILE *fPtr = NULL;
> double indata[262144][2];

In C you need to use #define or an enum constant for this sort of
number.  I imagine this code comes from C++ whose rule allow using const
ints for array sizes at file scope.  That's probably why you've ended up
repeating the number.

I'd limit the number of file-scope objects (globals in the vernacular)
to the very minimum.  Certainly the line buffer and the FILE pointer
should not really be here.

>
> To open and read the file I use:
> void readFile(FILE *fPtr, double a[][2])
> {
>   assert(fPtr != NULL);
>   assert(a != NULL);
>
>   bzero(&data[0], 64*sizeof(char));

bzero is a non-standard function.  Nothing wrong with that, but since C
has memset which does the same job, there is really no need to use
bzero.

sizeof (char) is 1 by definition, but you should probably just use the
line buffer size directly:

  memset(data, 0, sizeof data);

Finally, there's no need to zero the line buffer anyway!

>   while(fgets(&data[0], 64, fPtr) != NULL)

Again, I'd use the array size directly:

   while(fgets(data, sizeof data, fPtr) != NULL)

and I prefer data to &data[0] but that's very much a style detail.
   
>   {
>     parsestring(&data[0], a);
>     bzero(&data[0], 64*sizeof(char));
>   }
>
> }
>
> To parse each character string read in I use:
> void parsestring(char *cp, double a[][2])
> {

I find this function is too complex.  You could use sscanf instead like
this:

  int row;
  double d1, d2;
  if (sscanf(cp, "%d %lf %lf", &row, &d1, &d2) == 3) {
      a[row][0] = d1;
      a[row][1] = d2;
  }

You might add further checks such as ensuring that row is in range.
This raises the question of what to do when there is some error in the
data.  I suggest that parsestring return an int (a bool for modern C) to
indicate that all is well.  You can then write

  int n_pairs = 0;
  while(fgets(data, sizeof data, fPtr) != NULL &&
        parsestring(data, a))
           n_pairs += 1;
  if (!feof(fPtr))
      fprintf(stderr, "Error reading data near line %d.\n", n_pairs);

<snip>
-- 
Ben.

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Thread

Please help -- cannot read double data from file into array dakupoto@gmail.com - 2015-11-17 00:39 -0800
  Re: Please help -- cannot read double data from file into array Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-17 00:54 -0800
  Re: Please help -- cannot read double data from file into array gamo <gamo@telecable.es> - 2015-11-17 11:36 +0100
    Re: Please help -- cannot read double data from file into array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 11:04 +0000
  Re: Please help -- cannot read double data from file into array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 11:02 +0000
  Re: Please help -- cannot read double data from file into array James Kuyper <jameskuyper@verizon.net> - 2015-11-17 06:51 -0500
  Re: Please help -- cannot read double data from file into array BartC <bc@freeuk.com> - 2015-11-17 12:08 +0000
    Re: Please help -- cannot read double data from file into array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 13:28 +0000
      Re: Please help -- cannot read double data from file into array BartC <bc@freeuk.com> - 2015-11-17 14:20 +0000
        Re: Please help -- cannot read double data from file into array dakupoto@gmail.com - 2015-11-17 20:50 -0800
          Re: Please help -- cannot read double data from file into array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-18 11:22 +0000
            Re: Please help -- cannot read double data from file into array BartC <bc@freeuk.com> - 2015-11-18 12:15 +0000
            Re: Please help -- cannot read double data from file into array dakupoto@gmail.com - 2015-11-18 23:07 -0800
              Re: Please help -- cannot read double data from file into array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 10:41 +0000
              Re: Please help -- cannot read double data from file into array BartC <bc@freeuk.com> - 2015-11-19 11:13 +0000

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