realloc inside a routine

I wish to increase the size of an array inside a function, since I don't know the size of the array before I call the function.

I would think I could do (for example):

Code:

char log_filename[100];
double *buf = NULL;
int buf_len;

sprintf(log_filename, "log.txt");

fill_array(log_filename, buf, &buf_len);
fprintf(stderr, "buf[0]=%f\n", buf[0]);

void fill_array(char *log_filename, double *buf, int *buf_len) {
  int i = 0;
  FILE *fd;
  double time;

  fd = fopen(log_filename, "r");

  while (fscanf(fd_cam, "%lf\n", &time) != EOF) {
    times = (double *) realloc(times, (i + 1) * sizeof(double));
    times[i] = time;
    i++;
  }

}

But I get a seg fault, cause the memory is only accessible inside the fill_array() routine. How can I write such a routine, so it is accessible outside the routine. Thx.

Are those statements in main? If so, realloc is going to fail hard when you pass it the garbage pointer buf; make sure it's NULL before you send it off.

Originally Posted by tabstop

Are those statements in main? If so, realloc is going to fail hard when you pass it the garbage pointer buf; make sure it's NULL before you send it off.

The routine is in another .c file and the calls to it are in a main() routine set. Except the buf variable is a global variable.

And yes the buf is set to NULL first. Sorry forgot to add that in my example.

The function can only change its local copy of buf (presumably = "times" in your example). If you want to be able to change the value of buf, you must pass a pointer to it.

Originally Posted by tabstop

The function can only change its local copy of buf (presumably = "times" in your example). If you want to be able to change the value of buf, you must pass a pointer to it.

But I have passed it a pointer.

Or do you mean doing?:

Code:

char log_filename[100];
double *buf = NULL;
int buf_len;

sprintf(log_filename, "log.txt");

fill_array(log_filename, &buf, &buf_len);
fprintf(stderr, "buf[0]=%f\n", buf[0]);

void fill_array(char *log_filename, double **buf, int *buf_len) {
  int i = 0;
  FILE *fd;
  double time;

  fd = fopen(log_filename, "r");

  while (fscanf(fd_cam, "%lf\n", &time) != EOF) {
    *times = (double *) realloc(*times, (i + 1) * sizeof(double));
    (*times)[i] = time;
    i++;
  }

}

That works. Thanks...