Is there a GCC preprocessor directive to check if the code is being compiled on a 64 bit machine?

Question

I am trying to do something like the following;

#ifdef 64-bit
    #define DECIMAL_FORMAT %ld
#else
    #define DECIMAL_FORMAT %d
#endif
.
intptr_t d;  
.
printf(“Some message with DECIMAL_FORMAT in the middle of it\n”, d);

The variable 'd' being of the type 'intptr_t' needs '%d' format specifier on 32 bit machines and format specifier '%ld' on 64 bit machines. I am looking a solution to be able to compile the code on both 32 bit machines and 64 bit machines without making changes to the GCC command line or the source code.

Answer 1

I think __LP64__ might be what you're looking for. See http://gcc.gnu.org/onlinedocs/gcc-4.1.2/cpp/Common-Predefined-Macros.html

Maybe a better way to go, though, is to use the %p specifier to printf() instead of %ld or %d. Then you don't even have to worry what your pointer size is.