Is this Ok? (?:)

[Jerald Fijerald]

Hi all.

I was wondering if this expression is ok and has not any undefined
behaviors (bad style is not an issue):

int x;
x = a > 0 ? a [i++] : 1000;

I believe it is ok because in the case

x ? i++ : 0;

'i' is not incremented if x==0.
So it is ok, yes?

Thanks,

Gerald.

 

[Joona I Palaste]

Hi all.

I was wondering if this expression is ok and has not any undefined
behaviors (bad style is not an issue):

int x;
x = a > 0 ? a [i++] : 1000;

I believe it is ok because in the case

x ? i++ : 0;

'i' is not incremented if x==0.
So it is ok, yes?

This is completely OK, safe, kosher and hunky-dory. The ?: operator
constitutes a sequence point, so a>0 is guaranteed to have fully
evaluated before either a[i++] or 1000 can begin evaluating.

 

[Dan Pop]

Hi all.

I was wondering if this expression is ok and has not any undefined
behaviors (bad style is not an issue):

int x;
x = a > 0 ? a [i++] : 1000;

I believe it is ok because in the case

x ? i++ : 0;

'i' is not incremented if x==0.
So it is ok, yes?

This is completely OK, safe, kosher and hunky-dory. The ?: operator
constitutes a sequence point, so a>0 is guaranteed to have fully
evaluated before either a[i++] or 1000 can begin evaluating.

More precisely, there is a sequence point after the evaluation of the
condition of the ?: operator, so this statement is the equivalent of

if (a > 0) x = a[i++];
else x = 1000;

in the abstract C machine.

Dan