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Re: [libvirt] [PATCHv2] storage_encryption: silence clang warning



On 05/10/2010 01:02 PM, Jim Meyering wrote:
> Eric Blake wrote:
>> For printf("%*s",foo,bar), clang complains if foo is not int:
>>
>> warning: field width should have type 'int', but argument has
>> type 'unsigned int' [-Wformat]
>>
>>  virStorageEncryptionSecretFormat(virBufferPtr buf,
>>                                   virStorageEncryptionSecretPtr secret,
>> -                                 unsigned int indent)
>> +                                 int indent)
> 
> "unsigned int" sounds like the right type to me, since
> "indent" never goes negative.  And using the unsigned type
> seems to be in line with policy in HACKING:
> 
>     If a variable is counting something, be sure to declare it with an
>     unsigned type.

But printf("%*s", indent, string) would indeed behave differently if
indent goes negative (if signed) or larger than INT_MAX (if unsigned),
so clang's warning is realistic, and worth silencing in our quest to get
a clean clang build.  About the only other thing I could think of to do
that would avoid confusion and also to avoid casts is to keep the public
interface with unsigned int, then add an intermediate helper variable:

int real_indent = indent;

and use real_indent in the printf call, but that seems like overkill.

> 
> Of course, avoiding casts is good, too, but IMHO, not if
> it makes us obfuscate (even ever so slightly) the types we use.

Well, the real point of this patch was to silence a compiler warning
(not that we'd ever planning on passing an indent > 2G).  Given Dave's
ACK, I went ahead and applied v2 as proposed, even if it does slightly
obfuscate the usage.

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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