I know this has been questioned many times on SO, but my problem is specific to ANSI C (C89).
In C99 there are the sub-specifiers z and t, which are not supported in ANSI C.
What about using the p specifier?
size_t is an implementation-defined unsigned integer type. ptrdiff_t is an implementation-defined signed integer type.
In C89/C90 (commonly, but strictly speaking incorrectly, referred to as "ANSI C"), there are no special format specifiers for these types. But the widest integer types are long int and unsigned long int, which of course do have their own format specifiers.
To print a size_t value, cast it to unsigned long and use "%lu".
To print a ptrdiff_t value, cast it to long and use "%ld".
Note that if your code is then compiled with a C99 or C11 compiler, it's possible that size_t and/or ptrdiff_t could be wider than long, and the code could fail. (As I recall the 64-bit Windows interface has 32-bit long, so that could be an issue in practice.)
In C99 and later, just use %zu for size_t and %td for ptrdiff_t. If you want your code to be really portable, consider using #if to test the value of __STDC_VERSION__.
You could also run into problems if you have a compiler that only partially conforms to C99 or C11. You might have a compiler that doesn't fully support C99, but that does provide long long. But for the purpose of printing a size_t value, that's only going to be an issue if the value you're printing actually exceeds ULONG_MAX, which is at least 232-1. For a ptrdiff_t value, converting to long is OK as long as it doesn't exceed LONG_MAX, which is at least 231-1.
Finally, if you happen to know that the values you're printing aren't too big, you can get away with casting to int and using %d. I recommend casting to unsigned long or long, but int is OK for quick-and-dirty code.
What about using the
pspecifier?
No, %p is only for pointers of type void*, and in any case the output format is implementation-defined (it's commonly hex, but I've seen other representations).