Re: [Discuss-gnuradio] Regarding gr_squelch_base_cc.cc

[Marcus D. Leech]

On 04/29/2010 04:55 AM, Mattias Kjellsson wrote:
>
> 61:
> 62: case ST_UNMUTED:
> 63: if (mute())
> 64:     d_state = d_ramp ? ST_DECAY : ST_MUTED;    // If not ramping,
> go straight to muted
> 65: break;
>
> It might be that I don't fully understand the "?"- construct, but if I
> try to translate line 64 into an if- statement, I would do it (with my
> understanding) to something like:
>
> if(d_state = d_ramp){
>    d_state = ST_DECAY;
> }
> else{
>    d_state = ST_MUTED;
> }
>
> But this can't be the way since this will always set d_state =
> ST_DECAY (?) Or it could be the way, but in that case... Why the crazy
> ?- construct?
>
> As I said earlier, I'm scared and confused, since the code does it's
> job but it looks very... Suspicious
>
> BR
> Mattias
>
>
>
Ah, conditional expressions.

Let's deal with line 64:

d_state = d_ramp ? ST_DECAY : ST_MUTED;    // If not ramping, go
straight to muted

Translated into "conventional" conditionals:

if (d_ramp != 0)
{
    d_state = ST_DECAY;
}
else
{
    d_state = ST_MUTED;
}

In C, you can have a condition expression that just mentions the
variable name, without any explicit
  comparision operator:

if (foo)
{
    ...
}

Which in another language would be:

if (foo not-equal 0)
{
}



So, the "?" operator isn't all that crazy after all:

    (condition) ? (clause-to-execute-if-true) : (clause-to-execute-if-false)




-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org