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.

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;
}