returning an object in XS

bipham has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: returning an object in XS by davido (Cardinal) on Feb 29, 2012 at 03:52 UTC
There needs to be a typemap that will explain to Perl how to bind a `rect *` to a Perl structure of some sort. There are several CPAN modules that help to simplify the process. The one I'm most familiar with is Inline::CPP. But I'm highly biased. The gist of it is that you can create a C++ class that maps to a Perl class. The constructor becomes `new()`. The destructor becomes `DESTROY()`, and so on. The docs for Inline::C, Inline::C-Cookbook, and Inline::CPP are required reading in getting started with it. But it's fun (if you're slightly masochistic) once you get the hang of it. Inline::Struct is compatible with C (ie, doesn't require C++), and will bind C structures to Perl objects too. There was a time when Inline::CPP wasn't installing on the vast majority of systems out there. Over the last few months we've gotten it to the point that there's only one class of smoke testers that are still having trouble with it (NetBSD -- Any NetBSD pros get in touch with me so we can try to figure it out). Most other common platforms are able to install it and use it. There's also an email list where people can answer questions about the Inline modules: inline@perl.org. See http://lists.perl.org for details. Dave	[reply] [d/l] [select]
Re^2: returning an object in XS by bipham (Novice) on Feb 29, 2012 at 04:23 UTC
Thanks David, I will give it a try. I'll let you know of the result. Best regards,	[reply]
Re^3: returning an object in XS by davido (Cardinal) on Feb 29, 2012 at 04:43 UTC
I should mention that if you happen to be one of the unfortunate few for whom it doesn't install, download the latest dev release tarball, unpack it, and perform the mantra. Often the dev releases include tweaks undergoing smoke testing to 'PASS' additional platforms. Dave	[reply]
Re^4: returning an object in XS by bipham (Novice) on Feb 29, 2012 at 21:07 UTC
Re^5: returning an object in XS by davido (Cardinal) on Feb 29, 2012 at 23:23 UTC
Re: returning an object in XS by ikegami (Patriarch) on Feb 29, 2012 at 07:18 UTC
By the way, `*result = r;` is wrong. You're writing to unallocated memory. You need to allocate a `rect` first, and place a pointer to it in `result`. That also means the code calling your function will have to free it, which makes it wholly inappropriate for an XS function to return this. Sorry, don't know how to call C++ code from C, so I can't help you more than that.	[reply] [d/l] [select]
Re^2: returning an object in XS by bipham (Novice) on Feb 29, 2012 at 20:40 UTC
Hi Ikegami, After I fixed it, it passed but then it gives me another error shown below * glibc detected * free(): invalid next size (fast): 0x000000000089aaa0 *** Abort I don't know what happen, would you please help? The code is posted below. By the way, is that possible you can scan thru my code to see if I am doing what I supposed to do? Thanks Ikehami, MODULE = nDB PACKAGE = geom REQUIRE: 1.925 SV* get_bbox(rects) SV* rects INIT: rect* result; rect** arrRects; I32 nRects = 0; SV* sv; SV* rv = newRV_noinc(sv); if (rv == NULL) warn("RV has not been created sucessfully!\n"); SV** ssv; double minx,miny,maxx,maxy,tmp_minx,tmp_miny,tmp_maxx,tmp_maxy; int n; if ((!SvROK(rects))\|\|(SvTYPE(SvRV(rects)) != SVt_PVAV)\|\|((nRects = +av_len((AV)SvRV(rects))) < 0)) { XSRETURN_UNDEF; } arrRects = (rect)safemalloc(sizeof(rect)(nRects)); for (n=0;n<=nRects;n++) { ssv = av_fetch((AV)SvRV(rects), n, 0); if (ssv != NULL) { arrRects[n] = (rect)malloc(sizeof(rect)); if (arrRects[n] == NULL) { warn("get_bbox: unable to malloc rect\n"); } else { arrRects[n] = (rect)SvIV((SV)SvRV(ssv)); } } } CODE: minx = (arrRects)->x1(); miny = (arrRects)->y1(); maxx = (arrRects)->x2(); maxy = (arrRects)->y2(); for (n=1;n<=nRects;n++) { tmp_minx = ((arrRects+n))->x1(); tmp_miny = ((arrRects+n))->y1(); tmp_maxx = ((arrRects+n))->x2(); tmp_maxy = ((arrRects+n))->y2(); if (tmp_minx < minx) minx = tmp_minx; if (tmp_miny < miny) miny = tmp_miny; if (tmp_maxx > maxx) maxx = tmp_maxx; if (tmp_maxy > maxy) maxy = tmp_maxy; } result = (rect)malloc(sizeof(rect)); rect r(minx,miny,maxx,maxy); *result = r; sv_setref_iv(rv,"rect",(IV) result); RETVAL = rv; OUTPUT: RETVAL [download]	[reply] [d/l]
Re^3: returning an object in XS by bipham (Novice) on Feb 29, 2012 at 21:15 UTC
Oh I found it. The line result = (rect)safemalloc(sizeof(rect)); should be result = (rect*)safemalloc(sizeof(rect)); Regards,	[reply]
Re^2: returning an object in XS by bipham (Novice) on Feb 29, 2012 at 19:50 UTC
Thanks Ikegami, I really appreciate your advice. I will fix this and see if it passed.	[reply]
Re: returning an object in XS by BrowserUk (Patriarch) on Feb 29, 2012 at 03:52 UTC
`rect r(minx,miny,maxx,maxy);` What language is that? It doesn't look like valid C to me? `r()` is a function taking 4 doubles, but what is the `rect` prefix doing? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l] [select]
Re^2: returning an object in XS by ikegami (Patriarch) on Feb 29, 2012 at 07:21 UTC
It's C++, not C.	[reply]
Re^3: returning an object in XS by BrowserUk (Patriarch) on Feb 29, 2012 at 07:35 UTC
It's C++, It still doesn't look like any syntax I'm familiar with? It's been a while since I did any serious C++, but even so? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply]
Re^4: returning an object in XS by ikegami (Patriarch) on Feb 29, 2012 at 18:55 UTC
Re^5: returning an object in XS by BrowserUk (Patriarch) on Feb 29, 2012 at 19:18 UTC
Some notes below your chosen depth have not been shown here
Re^2: returning an object in XS by bipham (Novice) on Feb 29, 2012 at 04:20 UTC
Hi BrowserUK, that was just my class rect constructor. I didn't put it in the code. I'm sorry	[reply]
Re^3: returning an object in XS by BrowserUk (Patriarch) on Feb 29, 2012 at 05:11 UTC
that was just my class rect constructor. Is that a macro? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply]