Where in the C standard does it specify the corresponding argument for %n in fscanf shall be a pointer to int

Where in the C23 draft (or in any C standard) does it mention the corresponding argument for the conversion specification %n shall be a pointer to int

The exact type is specified by the length modifier as specified in section 7.23.6.2p11. It states that the hh, h, l, ll, j, t, and z modifiers can be applied to the n format specifier to specify that the argument points to a char, short, long, long long, intmaxt, ptrdifft, or size_t respectively.

Starting with C23, the documentation for the d, i, o, u, and x format specifiers were updated (and b was added) to explicitly state that a missing length modifier means the argument is a int or unsigned int . Prior to that, they were the same as n in that this wasn't explicitly stated.

Given that 7.23.6.2p11 states that length modifiers apply to n going back to at least C11 and that the documentation for d, i, o, u, and x were updated, this is likely an oversight.

Had your code used %lln as the full format specifier you would have gotten the expected results.