Why Is Escaping Data Considered So Magical?

[Jorgen Grahn]

On Mon, 2010-06-28, Kushal Kumaran wrote:
> On Mon, Jun 28, 2010 at 2:00 AM, Jorgen Grahn <grahn+nntp at snipabacken.se> wrote:
>> On Sun, 2010-06-27, Lawrence D'Oliveiro wrote:
>>> In message <roy-854954.20435125062010 at news.panix.com>, Roy Smith wrote:
>>>
>>>> I recently fixed a bug in some production code.  The programmer was
>>>> careful to use snprintf() to avoid buffer overflows.  The only problem
>>>> is, he wrote something along the lines of:
>>>>
>>>> snprintf(buf, strlen(foo), foo);
>>>
>>> A long while ago I came up with this macro:
>>>
>>>     #define Descr(v) &v, sizeof v
>>>
>>> making the correct version of the above become
>>>
>>>     snprintf(Descr(buf), foo);
>>
>> This is off-topic, but I believe snprintf() in C can *never* safely be
>> the only thing you do to the buffer: you also have to NUL-terminate it
>> manually in some corner cases. See the documentation.
>
> snprintf goes to great lengths to be safe, in fact.  You might be
> thinking of strncpy.

Yes, it was indeed strncpy I was thinking of. Thanks.

But actually, the snprintf(3) man page I have is not 100% clear on
this issue, so last time I used it, I added a manual NUL-termination
plus a comment saying I wasn't sure it was needed.  I normally use C++
or Python, so I am a bit rusty on these things.

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .  .
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