How to pass a function reference from C to perl

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

Dear All, I wonder if any of you can help me, I am new to XS and want to call a C function from perl. It is actually a pointer to a function which is a member of a structure. A part of the C header file is as follows:

typedef struct _mystruct1 {
    int val;
    int (* init) (void *object1, void **object2);
} mystruct1;

typedef struct _mystruct2 {
    mystruct *ptr;
} mystruct2;
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In the C code I have:

mystruct2 *mine;
int res;
struct obj *object1, **object2;
.....

mine->ptr->val = 100;
res = mine->ptr->init(object1, object2);
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and I want to be able to say the same from perl, i.e.:

print "$mine->{"ptr"}->{"val"}";            # This seems to work
$mine->{"ptr"}->{"init"}(object1, object2); # This does not work
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To do that I used an XS program which has the following:

rh = (HV *)sv_2mortal((SV *)newHV());
hv_store(rh, "val", 3, newSViv(mine->ptr->val), 0);
hv_store(rh, "init", 4, newRV((SV *)mine->ptr->init), 0); # This line 
+did not work
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I have tried to find out the type of the return pointer as in:

if (SvROK ((SV *) mine->ptr->init)) {
    type = SvTYPE(SvRV((SV *)mine->ptr->init));
    printf ("Something ..%d", type);
}
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but both statements failed ...

Any help appreciated ...

Maged Messeh

Comment on How to pass a function reference from C to perl Select or Download Code

Replies are listed 'Best First'.
Re: How to pass a function reference from C to perl by Matts (Deacon) on May 21, 2002 at 19:20 UTC
You can't do that. Perl has different calling conventions to C. You can only call a C function from within C-space. So you'll have to have some sort of XS function that calls your init function. See the XS Cookbook which may have an example of storing and calling a function pointer.	[reply]
Re: Re: How to pass a function reference from C to perl by Anonymous Monk on May 22, 2002 at 11:03 UTC
This in fact what I am trying to do (write an XS function).. but no success so far	[reply]
Re: How to pass a function reference from C to perl by rsteinke (Scribe) on May 21, 2002 at 22:18 UTC
What you probably want to do is convert the function pointer to an integer, and pass it as an IV. This is how perl handles pointers to blessed C objects created in XSUBs, so it should also work for function pointers. When perl calls the C code, convert the IV back to a function pointer and do the call. Alternately, you can pass mystruct1 as a blessed object. There's a neat tutorial on how to do this here.	[reply]