The printf and scanf families of functions in C consume a handful of primitive format specifiers that correspond to the fundamental data types – %d for int, %llu for unsigned long long int, etc.
However, there are a large number of standardized type aliases that one would like to use in practice, such as int32fast_t, and one cannot and should not have to know the underlying fundamental type. For the aliases in stdint.h, the C standard thankfully specifies a set of macros to generate the corresponding format strings, like PRI32, in inttypes.h.
Is there an analogous set of macros for Posix? Posix has tons of opaque types like ssize_t, pid_t, rlim_t, suseconds_t, etc, which are all variations on the basic intgral types. How can one portably use those types in format strings?
The sfio package (part of AT&T Labs' open source AST software) has functions analogous to printf and scanf which let you specify the size of the numeric value (typically using sizeof()) as an additional parameter. Some examples:
sfprintf(sfstdout, "%I*d", sizeof(intval), intval);
sfscanf(sfstdin, "%I*f", sizeof(fltval), &fltval);
USENIX paper: Extended Data Formatting Using Sfio .
Posix guarantees that sys/types.h values are an "arithmetic type of appropriate length" with a few others as being further specified as unsigned or signed 'extended length'. The only standards-acceptable way to output those would be to transfer it via cast in the largest appropriate language type (u)intmax_t and then output that.
Inputting them would be more dangerous (i.e., not possible in a standards-compliant fashion) as it would be difficult to guarantee your conversion to the base type didn't overflow something.
