How to do file I/O with bool in C?

Should I treat a bool variable like an int when doing file I/O?
I mean is it correct to use the following code snippet?

bool b = true;
FILE *fp1, *fp2;
...
fprintf(fp1, "%d", b);
fscanf(fp2, "%d", &b);

I'd like to know the answer based on ISO C specifications.

Solution

Should I treat a bool variable like an int when doing file I/O?

No, not for input.
Yes, OK to use for output as the bool is converted to an int as part of being a ... argument and that int matches "%d".

I mean is it correct to use ...

Not certainly. It might work. It is undefined behavior (UB).

I'd like to know the answer based on ISO C specifications.

There is no C specified way to read a bool via fscanf() and friends.

bool lacks a scanf() input specifier.
The size of bool may differ from int. It might be the same as char or others.
If input like "0", "1" used and "true", "false" not needed, read in an int and convert.

bool b = true;
FILE *fp1, *fp2;
...
fprintf(fp1, "%d", b);
int tmp;
fscanf(fp2, "%d", &tmp);
b = tmp;

Alternatively, use a string.

char tmp[2];
fscanf(fp2, "%1[0-1]", tmp);
b = tmp[0] == '1';

Additional work needed to accept "t", "FalsE", ...
Of course the return value of scanf() should be checked.
I'd consider a helper function:

Rough idea.  (Not really that great, just for illustration.)

// Read `bool` from `stdin`. Return 1 (success), EOF(end-of-file) and 0 in other cases.
int scan_bool(bool *b) {
  char buf[2];
  int cnt = scanf("%1[01tfTF]", buf);
  if (cnt != 1) {
    return cnt;
  }
  *b = buf[0] == '1' || buf[0] == 't' || buf[0] == 'T';
  return 1;
}