Sizes of data types

The 32- and 64-bit versions of QNX Neutrino use different C Language Data Type Models:

32-bit uses ILP32: integers, long integers, and pointers are 32 bits long.
64-bit uses LP64: long integers and pointers are 64 bits long.

The sizes of the basic data types are as follows:

Data type	32-bit	64-bit
char	8	8
int	32	32
long	32	64^a
long long	64	64
off_t	signed 32	signed 64^b
paddr_t	unsigned 32	unsigned 64^b
ptrdiff_t	32	64
short	16	16
size_t, ssize_t	32	64
time_t	unsigned 32	signed 64^b
uintptr_t, intptr_t	32	64
void *	32	64

^a 64-bit Windows uses 32 bits for a long because there's a lot of code that assumes that a long and an int are the same size. 64-bit Unix-type OSs use 64 bits for a long.

^b These changes aren't linked to 64-bit addresses, but this is a convenient time to make them.

Many compound types have changed in size, including the following:

struct sigevent
union sigval
siginfo_t
struct iovec
struct utimbuf
struct sigaction
struct _timer_info
struct timeval
and anything else that includes a base type whose size varies

When we extended the structures, we defined additional versions for 32- and 64-bits. For example, in addition to struct sigevent, we've defined struct __sigevent32 and struct __sigevent64 that have the correctly sized fields. These additional types let you access—for example—the 32-bit structure in a program compiled for 64 bits. The fields might not be of the same type as in the original structure, but they'll be the correct size.

Because of all these changes, you need to be careful with data types. For example:

NULL is now defined as (void *) 0 instead of just 0, so it no longer fits in an int or char. Don't use NULL as the terminating character in a string.
int and unsigned can't hold pointers or pointer differences anymore. Use uintptr_t to cast pointers to an integer type.
Use size_t or ptrdiff_t to hold the result of subtracting one pointer from another.
pointer & ~unsigned masks out more bits than you might expect. Use pointer & ~uintptr_t instead.

You can use the PRI* macros that are defined in <inttypes.h> to simplify calls to printf() that involve integers whose conversion specifier is different in 32- and 64-bit architectures.

Note: You can use the -Wconversion compiler option to generate warnings about any implicit conversions that could alter a value. This option isn't enabled by -Wall or -Wextra, so you have to specify it explicitly. For more information, see the gcc documentation at https://gcc.gnu.org/onlinedocs/gcc/.