On 10/05/2012 10:17 AM, Eric Blake wrote: > On 10/05/2012 10:06 AM, Andreas Schwab wrote: >> Chet Ramey <chet.ra...@case.edu> writes: >> >>> Why would you say there's a restriction against using casts or sizeof in >>> a macro like this? >> >> Because it must expand to a valid preprocessor expression. > > C99 5.2.4.2.1 > > Sizes of integer types <limits.h> > 1. The values given below shall be replaced by constant expressions > suitable for use in #if preprocessing directives. Moreover, except for > CHAR_BIT and MB_LEN_MAX, the following shall be replaced by expressions > that have the same type as would an expression that is an object of the > corresponding type converted according to the integer promotions. > > <stdint.h> and <limits.h> are the two main headers that are this > explicit about various macros being suitable for use in preprocessor > arithmetic, and preprocessor arithmetic cannot use casts or sizeof.
And I think this is a bug in POSIX; POSIX says: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_372 Symbolic Constant An object-like macro defined with a constant value. Unless stated otherwise, the following shall apply to every symbolic constant: • It expands to a compile-time constant expression with an integer type. • It may be defined as another type of constant—e.g., an enumeration constant—as well as being a macro. • It need not be usable in #if preprocessing directives. But nowhere in <limits.h> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html#tag_13_23_03_06 does it state that these macros inherited from C99 have the requirement of also being usable in #if preprocessing. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
signature.asc
Description: OpenPGP digital signature
