I recently stumbled on a glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=13575
and note that cygwin has the same bug in 32 bit.
test case 1:
$ cat <<\EOF | gcc -E -P - | grep size_t
#include <stdint.h>
#include <sys/types.h>
#include <limits.h>
size_t a = SIZE_MAX; ssize_t b = SSIZE_MAX;
EOF
On 32-bit, we see that both types are based on int:
typedef unsigned int size_t;
typedef signed int _ssize_t;
typedef _ssize_t ssize_t;
but that the constant for SSIZE_MAX is based on long
size_t a = (0xffffffffU); ssize_t b = (0x7fffffffL);
On 64-bit, we see that both types are based on long, as are the constants:
typedef long unsigned int size_t;
typedef long signed int _ssize_t;
typedef _ssize_t ssize_t;
size_t a = (0xffffffffffffffffUL); ssize_t b = (0x7fffffffffffffffL);
which is correct.
test case 2:
$ cat foo.c
#include <stdio.h>
#include <stdint.h>
#include <sys/types.h>
#include <limits.h>
int main(void) {
printf("%zu %zd\n", SIZE_MAX, SSIZE_MAX);
return 0;
}
$ gcc -o foo -Wall -Wformat=2 foo.c
Technically, there is NO portable way to pass ssize_t to printf without
a cast (the standards do not guarantee that %zd is ssize_t, because
ssize_t can be a different rank type than size_t) - but in practice,
most platforms use the same rank for the two types (both glibc and
Cygwin fall into this camp). Therefore, this should compile without
warning; 64-bit is fine, but 32-bit gripes:
foo.c: In function 'main':
foo.c:6:10: warning: format '%zd' expects argument of type 'signed
size_t', but argument 3 has type 'long int' [-Wformat=]
Also, recall that both SIZE_MAX and SSIZE_MAX must be usable in #if
expressions, so we can't use a cast to size_t in the macro, but instead
have to expand directly to an expression with the right type.
I'll probably try my hand at a patch later today.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
signature.asc
Description: OpenPGP digital signature
