llvm dev - Jul 2013 - [LLVMdev] [Patch] WinCOFFObjectWriter: fix for storing pointer to string table in header name field

On 23.07.2013 18:43, Reid Kleckner wrote:
> Is there a problem if the string is not null terminated?  If not, you can
> snprintf it right into place instead of doing sprintf+mempcy.
snprintf always null-terminates (and truncates if there's not enough space).

-Nico

On 23.07.2013 18:48, Nico Rieck wrote:> On 23.07.2013 18:43, Reid 
Kleckner wrote:
 >> Is there a problem if the string is not null terminated?  If not, 
you can
 >> snprintf it right into place instead of doing sprintf+mempcy.
 >
 > snprintf always null-terminates (and truncates if there's not enough
 > space).

Urgh, nevermind. Brain fart here.

-Nico

On Tue, Jul 23, 2013 at 12:48 PM, Nico Rieck <nico.rieck at gmail.com>
wrote:
> On 23.07.2013 18:43, Reid Kleckner wrote:
>
>> Is there a problem if the string is not null terminated?  If not, you
can
>> snprintf it right into place instead of doing sprintf+mempcy.
>>
>
> snprintf always null-terminates (and truncates if there's not enough
> space).

Nuh uh: "The _snprintf function formats and stores count or fewer
characters in buffer, and appends a terminating null character if the
formatted string length is strictly less than count characters."
http://msdn.microsoft.com/en-us/library/2ts7cx93(v=vs.100).aspx

Please don't assume snprintf always null terminates.

This may be Windows-specific behavior that you shouldn't rely on.  If
that's the case, ignore my suggestion.
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On 23.07.2013 18:55, Reid Kleckner wrote:
> Please don't assume snprintf always null terminates.
I'm reading C99 7.19.6.4 and C11 7.21.6.5 which says:

"If n is zero, nothing is written, and s may  be  a  null  pointer. 
Otherwise,  output  characters  beyond  the n-1st  are discarded rather 
than being written to the array, and a null character is written at the 
end of the characters actually written into the array."

and "Thus,  the  null-terminated  output  has  been
completely written if and only if the returned value is nonnegative and 
less than n."

-Nico

In article <CACs=tyLqAn7GNNobgwr+K96k-Zw1y5N16dzOeOB2O8OtrHyNig at
mail.gmail.com>,
    Reid Kleckner <rnk at google.com> writes:
> Nuh uh: "The _snprintf function formats and stores count or fewer
> characters in buffer, and appends a terminating null character if the
> formatted string length is strictly less than count characters."
> http://msdn.microsoft.com/en-us/library/2ts7cx93(v=vs.100).aspx
> 
> Please don't assume snprintf always null terminates.
> 
> This may be Windows-specific behavior that you shouldn't rely on.  If
> that's the case, ignore my suggestion.
Yes, _snprintf with MSVC is not a conforming C99 (or whatever) standard
implementation of snprintf.  I've filed a bug on it, but don't expect
a fix from them anytime soon as they deem it low priority.

This is just another reason to stay away from these error-prone C APIs
in C++ code.
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