Re: keeping binary data raw (char*)

I was sad to see that Inline::C's documentation doesn't even really hint at what happens if your C function returns a value of type "char*".

If you find your ExtUtils/typemap file you'll find the following lines (not together):

char *            T_PV
INPUT
T_PV
    $var = ($type)SvPV_nolen($arg)
OUTPUT
T_PV
    sv_setpv((SV*)$arg, $var);
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so returning a "char*" calls sv_setpv(). If you read perlguts you'll see a disappointingly vague hint that sv_setpv() sets the length of the scalar's string value based on strlen(str), which isn't appropriate for your "binary" string.

So you instead want to return a SV* type of value and (again, it is sad here that Inline::C doesn't even show how to do this) use something more like return svNEWpvn( str, len );.

So now you also have several places that could use documentation patches. /:

- tye

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Re^2: keeping binary data raw (char*) by syphilis (Archbishop) on Oct 26, 2007 at 16:32 UTC
I was sad to see that Inline::C's documentation doesn't even really hint at what happens if your C function returns a value of type "char".* In defense of Inline::C: 1) I wonder if Inline::C is under any obligation to document this; 2) There are a number of examples in `perldoc Inline::C-Cookbook` that do deal with `newSVpv` (usually as a `newSVpvf`) Cheers, Rob	[reply] [d/l] [select]
Re^3: keeping binary data raw (docs) by tye (Sage) on Oct 26, 2007 at 18:25 UTC
I don't get where you think the term "obligation" applies. Based on "obligation" I think you could delete most if not all of the Inline::C documentation. Rather than expecting the vague hints in Inline::C to lead to (a huge jump) ExtUtils/typemap then to perlguts then perlapi then "man strlen" to finally have the (C) '\0' character mentioned, I think it would be more than prudent for Inline::C to document this important and not obvious restriction and skip "typemap", "sv_setpv()", and "strlen()" and just say that a return value of type "char" only works for strings terminated by "\0" (and not containing any non-terminal "\0" characters). I also think an example of `SV` and `return newSVpvn( str, len );` deserves to be in the base manual, not burried in the "cookbook" (or the documentation of the restrictions on "char" should point directly to an appropriate "cookbook" example). It would certainly be better than the example that uses SvPVX(), a macro that should mostly never be used. But, of course, I don't find the author obligated* to do much of anything. - tye	[reply] [d/l] [select]
Re^3: keeping binary data raw (char*) by downer (Monk) on Oct 29, 2007 at 18:59 UTC
newSVpvf works perfectly. i wish i was good enough at C or C++ where i didnt need to make wrappers in perl for stuff like this. perl's I/O is so much more intuitive that either of these two.	[reply]