realloc inside a routine

[coletek]

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):

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.

[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.

[coletek]

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.

[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.

[coletek]

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?:

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...