Reading an array of floats from a file in C - arrays

Question

How can I retrieve an array of floating-point values from a file in C? This is the code I have used so far, but I am running into a segmentation fault(marked in my code where). If you see a less painful way of doing this that would be helpful as well.
The values are stored in the file with a single space after each value like so:
-667.0897114275529 544.6798599456312 -148.0586015260273 -323.4504101541069 .
// open file
FILE *fp;
fp = fopen(sig_file, "r");
if (fp == NULL){
printf("File opened incorrectly or is empty");
return 1;
}
// find file size
fseek(fp, 0L, SEEK_END);
long sz = ftell(fp);
fseek(fp, 0L, SEEK_SET);
// store file contents to f_contents
char *f_contents = 0;
f_contents = malloc(sz);
if (f_contents){
fread(f_contents, 1, sz, fp);
}
fclose(fp);
if (f_contents){
// find how many points are in the file
long pt_count = 0;
int i;
for (i=0; i<sz; i++){
if (f_contents[i] == ' '){
pt_count++;
}
}
// store points to a float array
double signal[pt_count];
char *pt;
pt = strtok(f_contents, " ");
// seg fault 11:
if (pt == NULL){
printf("error with pt");
return 1;
}
signal[0] = atof(pt);
//
for (i=1; i<pt_count; i++){
pt = strtok(NULL, " ");
signal[i] = atof(pt);
}
}
free(f_contents);

Answer 1

If you see a less painful way of doing this that would be helpful as well.
I haven't studied your code enough to identify the source of the segfault, because it should just be rewritten anyway. I might be inclined to do something more like this:
// open file
FILE *fp = fopen(sig_file, "r");
if (fp == NULL){
perror("fopen");
return 1;
}
size_t sz = 0;
for (int c = getc(fp); c != EOF; c = getc(fp)) {
if (c == ' ') sz++;
}
rewind(fp);
double signal[sz];
for (size_t i = 0; i < sz; i++) {
if (fscanf(fp, "%lf", &signal[i]) != 1) {
fclose(fp);
fputs("I/O error, malformed input, or premature EOF\n", stderr);
return 1;
}
}
fclose(fp);
If the file is long, then it might be worthwhile to read it all in one pass instead of counting elements first (and especially instead of slurping the entire file into memory). You can achieve such a one-pass read by storing the values in a more flexible data structure: some variety of linked list, or a dynamically allocated (and reallocated as necessary) array.
A linked list would need to be postprocessed into array form, but you might be able to use a dynamically allocated array as-is. You would need to use either a dynamically allocated array or a large-enough fixed-size array with a C implementation that does not support variable-length arrays, such as MS Visual Studio.

Answer 2

The first argument to strtok() must be a null-terminated string. fread() doesn't add a null terminator, and even if it did, you didn't allocate enough space for f_contents to hold it.
So use this code to allocate and fill in f_contents
f_contents = malloc(sz+1);
if (f_contents){
fread(f_contents, 1, sz, fp);
f_contents[sz] = '\0';
}
fclose(fp);