Issac Goldstand wrote:
>[snip]
>
>
>
>>>However, it seems that I've taken my eye off the ball with all these
>>>compilation problems and concerns over memory leaks: the
>>>PUSHi()/PUSHp() version of the XSUB above doesn't actually work properly!
>>>
>>>Instead of returning (42, "Forty-two"), it returns ("Forty-two",
>>>"Forty-two"). In general, if I use PUSHi() or PUSHp() to push N things
>>>onto the stack and then XSRETURN(N) then I seem to get N copies of the
>>>last return value that I pushed.
>>>
>>>
>>Only one TARG SV for the op. If you look at macros in pp.h
>>you will see
>>
>>PUSHi(i) STMT_START { sv_setiv(TARG, (IV)(i)); PUSHTARG; } STMT_END
>>
>>So it sets the one SV to the value, and then pushes the one SV.
>>
>>So it seems that PUSHi() et. al. are not suitable for list returns.
>>
>>
>>
>
>Could you clarify that a bit? Why not?
>
Well, if you call PUSHi() twice then all you're doing is setting the
value of TARG, pushing a pointer to it onto the stack, then changing the
value of TARG and pushing another pointer to it onto the stack. You end
up with two pointers to the same SV (TARG) on the stack, so of course
both return values are the same, namely, the last value that you set
TARG to.
This is (as I belatedly discovered) documented in perlguts -- see the
section entitled "Putting a C value on the Perl stack".
- Steve
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