CODEWITHSUNDEEP
cprintftypedef
user1532080
user1532080

Reputation: 305

printf and (signed) int of unknown size

I have a platform dependent type defined in my code: typedef uint64_t myType;

However on some more limited platform, it might be 32 bits.

How do I printf it? As in, in the current situation, I can use %llu, but if on another platform it's 32 bits, this is not the best idea.

I thought about using some macros, but would anyone know of a better way? I'd love to hear about some format specifier that could take the length from the next argument, for example.

Upvotes: 1

Views: 309

Answers (2)

paxdiablo
paxdiablo

Reputation: 882586

Since you have platform-specific types, it should be easy enough to use platform-specific format strings as well, something like:

#ifdef USING_64_bits
    typedef uint64_t myType;
    #define MY_TYPE_FMT PRIu64
#else
    typedef uint32_t myType;
    #define MY_TYPE_FMT PRIu32
#endif

Then you can use it with:

myType var1 = 42, var2 = 99;
printf ("%6" MY_TYPE_FMT ", %019" MY_TYPE_FMT "\n", var1, var2);

The extraction of the % from the format string allows you to insert other format specifiers dynamically, such as field widths and padding characters.

You'll also notice that I've avoided the %llu-style format specifiers, you should be using the more targeted ones in inttypes.h since the implementation will give you the correct one for your type.

Upvotes: 5

R.. GitHub STOP HELPING ICE
R.. GitHub STOP HELPING ICE

Reputation: 215567

Just cast it up to the largest-possible integer type matching the desired signedness and use the format for that, either:

printf("%jd", (intmax_t)x);

or:

printf("%ju", (uintmax_t)x);

(The question title asks for signed but the body is using unsigned examples, so I've covered both.)

This is a lot less ugly/more readable than using the PRI* macros suggested in the other answer, and also works for types where you don't inherently know the right PRI macro to use, like off_t.

Upvotes: 5

Related Questions