[ warning: more than you really wanted to know ahead ] Alvaro Herrera <alvhe...@alvh.no-ip.org> writes: > Tom Lane wrote: >> We have a workaround for that symbol in timezone/private.h: >> #ifndef SIZE_MAX >> #define SIZE_MAX ((size_t) -1) >> #endif >> and a bit of grepping finds other places that are using the (size_t) -1 >> trick explicitly. So what I'm tempted to do is move the above stanza >> into c.h.
> Sounds good to me. On closer inspection, C99 requires SIZE_MAX and related macros to be a "constant expression suitable for use in #if preprocessing directives", which we need for the fe-exec.c usage because it does #if INT_MAX >= (SIZE_MAX / 2) if (newSize > SIZE_MAX / sizeof(PGresAttValue *)) (We could maybe dispense with this #if check, but I feared that doing so would result in nanny-ish "expression is constant false" warnings from some compilers on 64-bit platforms.) Now, that cast doesn't really work in an #if expression. Some language lawyering leads me to conclude that in #if, a C compiler will interpret the above value of SIZE_MAX as "((0) -1)", or just signed -1. So fe-exec.c's test will surely evaluate to true, which seems like a safe outcome. But you could certainly imagine other cases where you get incorrect results if SIZE_MAX looks like a signed -1 to an #if-test. When I look into /usr/include/stdint.h on my Linux box, I find # if __WORDSIZE == 64 # define SIZE_MAX (18446744073709551615UL) # else # define SIZE_MAX (4294967295U) # endif so I thought about trying to duplicate that logic. We can certainly test SIZEOF_SIZE_T == 8 as a substitute for the #if condition. The hard part is arriving at a portable spelling of "UL", since it would need to be "ULL" instead on some platforms. We can't make use of our UINT64CONST macro because that includes a cast. So it seems like if we want to be 100% correct it would need to be something like #ifndef SIZE_MAX #if SIZEOF_SIZE_T == 8 #if SIZEOF_LONG == 8 #define SIZE_MAX (18446744073709551615UL) #else /* assume unsigned long long is what we need */ #define SIZE_MAX (18446744073709551615ULL) #endif #else /* 32-bit */ #define SIZE_MAX (4294967295U) #endif #endif That's mighty ugly. Is it worth the trouble, rather than trusting that the "(size_t) -1" trick will work? Given that we have so few needs for SIZE_MAX, I'm kind of inclined just to stick with the cast. I notice BTW that PG_INT64_MIN, PG_INT64_MAX, and PG_UINT64_MAX all contain casts and thus are equally risky to test in #if-tests. I see no at-risk code in our tree right now, but someday we might need to make those look something like the above, too. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers