[postgis-users] 1.3.3 Pre-Release Notice

[Chris LaReau]

Mark,

On Wed, Apr 09, 2008 at 10:05:35AM +0100, Mark Cave-Ayland wrote:
> Taking a look at the committed fix, I see that you have the following:
> 
> if ( sr_id && strcmp(sr_id,"-1") ) printf("SRID=%s;", sr_id);
> 
> I have a very strong feeling that evaluation order in C is unspecified, rather 
> than being from left to right; so for example the compiler could decide to 
> generate code that evaluates the strcmp() first, in which case it would 
> segfault on a NULL :( I think you would need to re-write something like this:
> 
> if (sr_id)
> 	if (strcmp(sr_id,"-1") ) printf("SRID=%s;", sr_id);

Your "very strong feeling" is wrong in this case. Evaluation order
for function arguments in C is not specified. However, '&&' and '||'
are not functions. In C/C++, and several other languages, '&&' and
'||' are short-circuit operators, NOT logical operators. Millions of
lines of C (or C++, Java, Perl, JavaScript, etc.) would crash or
otherwise fail if constructs like

    if (ptr && *ptr) { /* do something */ }

did not work as expected. See

    http://en.wikipedia.org/wiki/Short-circuit_evaluation

for a more complete description of this common computer language
feature.

Cheers,

Chris LaReau
Technology Primate
Korora, LLC