Reading binary data - finding min and max coordinates

Question

I have a binary data file. There are over 4 millions LIDAR data records. Every record is stored as four numbers - three floats (coordinates x, y, z) and one integer (unimportant now). I should implement a function which gets minimal and maximal coordinate in every axis. I wrote the code below, the algorithm looks to be very straightforward and simple, but it's not working (it returns every minimum as 0.0f and every maximum as 1.0f). Do I have anything wrong?

void get_min_max(const char *filename, float *a_min_x, float *a_max_x, float *a_min_y, float *a_max_y, float *a_min_z, float *a_max_z) {
  FILE *f = NULL;
  float x, y, z;
  float min_x, min_y, min_z, max_x, max_y, max_z;
  int l_type;

  f = fopen(filename, "rb");

  if (!f) {
    printf("No binary file read!\n");
    exit(-1);
  }

  min_x = min_y = min_z =  std::numeric_limits<float>::max();
  max_x = max_y = max_z = -std::numeric_limits<float>::max();

  while (true) {
    x = fread((void*)(&x), sizeof(x), 1, f);
    y = fread((void*)(&y), sizeof(y), 1, f);
    z = fread((void*)(&z), sizeof(z), 1, f);

    min_x = fminf(x, min_x);
    min_y = fminf(y, min_y);
    min_z = fminf(z, min_z);

    max_x = fmaxf(x, max_x);
    max_y = fmaxf(y, max_y);
    max_z = fmaxf(z, max_z);

    l_type = fread((void*)(&l_type), sizeof(l_type), 1, f);

    if (feof(f)) {
      break;
    }
  }

  fclose(f);

  *a_min_x = min_x;    // = 0.0f ???
  *a_min_y = min_y;    // = 0.0f ???
  *a_min_z = min_z;    // = 0.0f ???

  *a_max_x = max_x;    // = 1.0f ???
  *a_max_y = max_y;    // = 1.0f ???
  *a_max_z = max_z;    // = 1.0f ???
}

Answer 1

Your problem is assigning freads result into your variable:

x = fread(&x, ...)

First fread reads the data into x, then it returns the number of elements read (1), and then x becomes 1.0.

You should really learn how to use a debugger, you would have seen this very quickly.