Toying with fscanf to read/write sampling data to/from a file

demo.c

/* demo.c --

   Compile with:

     gcc -Wall -std=c11 -lm -o demo demo.c
*/

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

static char const * MY_PRIuSIZE;

typedef struct data_t	data_t;

struct data_t {
  size_t n;
  double *t;
  double *y;
};

void
write_data (FILE * stream, data_t const * D)
{
  fprintf(stream, "N=");
  fprintf(stream, MY_PRIuSIZE, D->n);
  fprintf(stream, "\nt=");
  for (size_t i=0; i<D->n; ++i) {
    fprintf(stream, "%lf;", D->t[i]);
  }
  fprintf(stream,"\ny=");
  for (size_t i=0; i<D->n; ++i) {
    fprintf(stream, "%lf;", D->y[i]);
  }
  fprintf(stream,"\n");
}

void
read_data (FILE * stream, data_t * D)
{
  fscanf(stream, "N=");
  fscanf(stream, MY_PRIuSIZE, &(D->n));
  fscanf(stream, "\nt=");
  for (size_t i=0; i<D->n; ++i) {
    fscanf(stream, "%lf;", &(D->t[i]));
  }
  fscanf(stream,"\ny=");
  for (size_t i=0; i<D->n; ++i) {
    fscanf(stream, "%lf;", &(D->y[i]));
  }
  fscanf(stream,"\n");
}

int
main (void)
{
  if (sizeof(unsigned int) == sizeof(size_t)) {
    MY_PRIuSIZE = "%u";
  } else if (sizeof(unsigned long int) == sizeof(size_t)) {
    MY_PRIuSIZE = "%lu";
  } else {
    exit(EXIT_FAILURE);
  }

  {
#undef NUM
#define NUM	32
    data_t	D = { .n = NUM };
    double	step = 0.01;

    D.t = malloc(sizeof(double) * D.n);
    D.y = malloc(sizeof(double) * D.n);

    D.t[0] = 0.0;
    D.y[0] = exp(D.t[0]);
    for (size_t i=1; i<D.n; ++i) {
      D.t[i] = step + D.t[i-1];
      D.y[i] = exp(D.t[i]);
    }

    {
      FILE *	stream = fopen("data.txt", "w+");

      write_data(stream, &D);
      fseek(stream, 0L, SEEK_SET);
      read_data(stream, &D);
      write_data(stderr, &D);
      fclose(stream);
    }
  }

  exit(EXIT_SUCCESS);
}

/* end of file */