Re: [Qemu-devel] [PATCH v2 0/3] require newer glib2 to enable autofree'ing of stack variables exiting scope

[Eric Blake]

On 7/31/19 9:04 AM, Alex Bennée wrote:
> 
> Daniel P. Berrangé <address@hidden> writes:
> 
>> Both GCC and CLang support a C extension attribute((cleanup)) which
>> allows you to define a function that is invoked when a stack variable
>> exits scope. This typically used to free the memory allocated to it,
>> though you're not restricted to this. For example it could be used to
>> unlock a mutex.
> <snip>
>>
>>     GOOD:
>>         g_autofree char *wibble = g_strdup("wibble")
>>      ...
>>      return g_steal_pointer(wibble);
>>
>>     g_steal_pointer is an inline function which simply copies
>>     the pointer to a new variable, and sets the original variable
>>     to NULL, thus avoiding cleanup.
> 
> Surely this is a particular use case where you wouldn't use g_autofree
> to declare the variable as you intending to return it to the outer scope?

Actually, it's still quite useful if you have intermediate returns:

g_autofree char *wibble = NULL;
if (something)
  return NULL;
wibble = g_strdup("wibble");
if (something_else)
  return NULL;
return g_steal_pointer(wibble);

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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