Re: [Qemu-devel] [PATCH] trace: Fix 'char **' compilation error in simple backend

[Eric Blake <eblake@redhat.com>]

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On 10/25/2016 09:46 PM, Fam Zheng wrote:
> On Tue, 10/25 21:29, Eric Blake wrote:
>> On 10/25/2016 08:59 PM, Fam Zheng wrote:
>>> Currently, the generated function body will do "strlen(arg)" but the
>>> argument could be 'char **'. Avoid that by exclusding such cases in
>>

>>>  def is_string(arg):
>>>      strtype = ('const char*', 'char*', 'const char *', 'char *')
>>> -    if arg.lstrip().startswith(strtype):
>>> +    non_strtype = ('const char**', 'char**', 'const char **', 'char **')
>>> +    arg_strip = arg.lstrip()
>>> +    if arg_strip.startswith(strtype) and not arg_strip.startswith(non_strtype):
>>
>> There may be a more compact way to write it, but I'm not enough of a
>> python expert to know offhand what else to suggest (it's not as simple
>> as string concatenation of strtype + '*', since strtype is a tuple
>> rather than a string).
> 
> Did you mean
> 
>     non_strtype = tuple(x + '*' for x in strtype)

Hmm, I guess that would work.

Or, what about a different approach, something like:
  if arg_strip.startswith(strtype) and no_multiple_star(arg_strip):
for some sane definition of no_multiple_star() that checks that there is
exactly one '*' in a string.  In C, I'd check roughly:
  p = strchr(str, '*');
  if (p && !strchr(p + 1, '*')) {
    // treat str as string
  }
but again, I'm not enough of an expert to pop that out late at night,
even if python has an easy one-liner way to express that.


> But personally I'd stick to the flatten version in this specific case for
> a bit more readability.

Indeed, and that's why I gave R-b as-is, even if it fails when there are
multiple 'const' qualifiers in a string with multiple '*' :)

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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