On Mon, Mar 22, 2010 at 03:21:06PM -0600, Eric Blake wrote:
On 03/22/2010 01:05 PM, Daniel P. Berrange wrote:
Use the new virDomainUpdateDeviceFlags API to allow the VNC password to be changed on the fly
* src/internal.h: Define STREQ_NULLABLE() which is like STREQ() but does not crash if either argument is NULL, and treats two NULLs as equal. ...
+++ b/src/internal.h @@ -58,6 +58,12 @@ # define STRCASENEQLEN(a,b,n) (strncasecmp(a,b,n) != 0) # define STRPREFIX(a,b) (strncmp(a,b,strlen(b)) == 0)
+# define STREQ_NULLABLE(a, b) \ + ((!a && !b) || (a && b && STREQ(a, b))) +# define STRNEQ_NULLABLE(a, b) \ + ((!a && b) || (a && !b) || (a && b && STRNEQ(a, b)))
This seems like an independently useful change, and one worth documenting in docs/hacking.html.in next to the existing documentation on STREQ. It also has a bug - it is under-parenthesized. And you can use ^ for compactness:
# define STREQ_NULLABLE(a, b) \ ((!(a) && !(b)) || ((a) && (b) && STREQ(a, b))) # define STRNEQ_NULLABLE(a, b) \ ((!(a) ^ !(b)) || ((a) && (b) && STRNEQ(a, b)))
Hmmm. The existing STREQ and STRNEQ only evaluate arguments once, but this evaluates arguments multiple times. Then again, so does the existing STRPREFIX. Are any of these three worth making static inline functions, rather than macros, to avoid side-effects of multiple evaluation?
I don't think the multiple evaluation matters - none of the uses of these macros pass in complex expressions where multiple evaluation would cause problems. THe args are always just constant strings, or char * pointers. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|