printf and %llu vs %lu on OS X

Question

Possible Duplicate:
how to printf uint64_t?

Why is it that on my 64-bit Mac (I am using Clang) the uint64_t type is unsigned long long while on 64-bit Ubuntu the uint64_t type is unsigned long?

This makes it very difficult for me to get my printf calls to not give compiler warnings (or indeed even to work) under both environments.

I can try to use macros to try to choose the correct string (#define LU either %llu or %lu, and in the process uglifying the printf strings a bit) but on the Mac I've got a 64-bit word size (so _LP64 would be defined and UINTPTR_MAX != 0xffffffff) and yet it still uses long long for the 64 bit int types.

// printf macro switch (for the uint64_t's)
#if UINTPTR_MAX == 0xffffffff 
   // 32-bit
#  define LU "%llu"
#else 
   // assume 64-bit
   // special case for OS X because it is strange
   // should actually check also for __MACH__ 
#  ifdef __APPLE__
#    define LU "%llu"
#  else
#    define LU "%lu"
#  endif
#endif

Solution 1

The macros are already defined for you in <cinttypes>. Try

printf("%"PRIu64, x);

Or, even better, use C++ features like

std::cout << x;

which will select the proper << operator for your variable type.

Solution 2

The answer is to promote via static cast:

some_type i = 5;
printf("our value is: %llu", (unsigned long long)i);

Solution 3

The underlying type of uint64_t can be whatever the implementation like as long as it is in fact 64 bits.

Obviously in C++ the preferred solution is to use iostreams instead of printf as then the problem disappears. But you can always just cast the value passed to printf to make the type always correct:

printf("%llu", static_cast<unsigned long long>(value));

Comments

[Steven Lu]

fatal error: 'cinttypes' file not found

[Bo Persson]

This is a C++11 header, so it depends on how compatible your compiler is. If supporting C99, there will be an <inttypes.h>.

[Steven Lu]

Ah, okay, thanks. I did actually find that file in the C++11 libc++. Well, hopefully this inttypes.h header is available on my other platforms as well, here's the replacement for my code snippet in the question: #define LU "%"PRIu64

[Steven Lu]

I have never seen %zu or %ju before. How standard is this?

[daxnitro]

It's standard and should be perfectly portable. cplusplus.com/reference/cstdio/printf

[Steven Lu]

Oh wow. Must have missed it.

[Steven Lu]

Hmm... Lengthens the code a bit.

[Johannes Overmann]

The std::cout << x; statement is not equivalent to the printf(). If you write the equivalent statement you will see why people still use printf() to format numbers. :-)

[Gonzalo Aguilar Delgado]

%zu is for size_t data types, that differ in different platforms so you can make sure the correct interpretation is made. Is basically the formatting of a size_t as unsinged.