On 04/27/2018 11:15 AM, Eric Blake wrote:
On 04/27/2018 02:20 AM, gaosheng cui wrote:
Hi,using ignore_value in libvirt source code to do function return value processing,but I can’t understand about it,can you give me some tips?thanks very much!
Is your question about what ignore_value() does?
Or, if your question is "Where is ignore_value defined", the answer is that libvirt uses gnulib, and gnulib's "ignore-value.h" (imported during ./bootstrap if you are building from git; if you are building a release tarball then it was already part of the tarball under lib/) contains this definition: /* Normally casting an expression to void discards its value, but GCC versions 3.4 and newer have __attribute__ ((__warn_unused_result__)) which may cause unwanted diagnostics in that case. Use __typeof__ and __extension__ to work around the problem, if the workaround is known to be needed. */ #if 3 < __GNUC__ + (4 <= __GNUC_MINOR__) # define ignore_value(x) \ (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; })) #else # define ignore_value(x) ((void) (x)) #endif -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org