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

Hi there, I have this function in C: 
TM_PageTranslation* findPageByEffective(u32 lpid, u32 pid, u64 EA);

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These are the types of each parameter: TM_PageTranslation - C struct u32 - unsigned int u64 - unsigned long long int This is my typemap: 
TYPEMAP
T_PageTranslation     T_PTROBJ
u64                   T_U_LONG_LONG
u64 *                 T_OPAQUEPTR
u32 *                 T_OPAQUEPTR
u32                   T_U_INT
##################################################
INPUT
T_U_LONG_LONG
    $var = (unsigned long long int)SvUV($arg)
##################################################
OUTPUT
T_U_LONG_LONG
    sv_setuv($arg, (UV)$var);

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(T_U_INT is defined in the default typemap) this is my XS code: 
typedef struct TM_PageTranslation * T_PageTranslation;
...
T_PageTranslation
findPageByEffective(lpid, pid, EA)
        u32 lpid
        u32 pid
        u64 EA

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When I run the make command I get the following warning: "trans.c:470: warning: assignment from incompatible pointer type" line 470 int rans.C is this: 
XS(XS_trans_findPageByEffective); /* prototype to pass -Wmissing-proto
+types */
XS(XS_trans_findPageByEffective)
{
#ifdef dVAR
    dVAR; dXSARGS;
#else
    dXSARGS;
#endif
    if (items != 3)
       croak_xs_usage(cv,  "lpid, pid, EA");
    {
    u32    lpid = (unsigned int)SvUV(ST(0));
    u32    pid = (unsigned int)SvUV(ST(1));
    u64    EA = (unsigned long long int)SvUV(ST(2));
    T_PageTranslation    RETVAL;

    RETVAL = findPageByEffective(lpid, pid, EA); <--- This is line 470
    ST(0) = sv_newmortal();
    sv_setref_pv(ST(0), "T_PageTranslation", (void*)RETVAL);
    }
    XSRETURN(1);
}

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How do I fixed this?

Replies are listed 'Best First'.
Re: perlXS assignment from incompatible pointer type
by Anonymous Monk on Mar 22, 2016 at 23:40 UTC
    And what about the definition of struct TM_PageTranslation? For all we know there is no such struct... Maybe it's something like 
    typedef struct {
    ...
} TM_PageTranslation;

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    If so, remove struct from typedef struct TM_PageTranslation * T_PageTranslation. That's the most likely cause of error, IMO.

    If that doesn't work, try to post SSCCE. See sscce.org for details.

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[d/l]
[select]
      I've taken a look at your previous posts and indeed... So, OP, you'll have to learn about a pretty dumb feature of C (that has nothing to do with XS per se). There is a difference between 
      typedef struct Foo {
   ...
} Foo;

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      and 
      typedef struct {
    ...
} Foo;

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      In the first case, you can use struct Foo and Foo interchangeably. I think... Compatibility rules for types in C are pretty complex and obscure. Anyway, in the second case you don't have struct Foo, you have just Foo which is a name for an anonymous struct (while Foo in struct Foo is not a name but a tag). Yes, it's pretty confusing... but don't worry: there are some things in C that are a lot more obscure and error prone than that :) I suggest you to avoid typedefs for the time being.
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[d/l]
[select]

        Regarding your first example: there's no compatibility problem. "A typedef declaration does not introduce a new type, only a synonym for the type so specified." If you didn't add qualifications, they are one and the same type (an alias).

[reply]
      You're a genius :) Thank you !!! Removed "struct" (and thanks for the lesson in structs)
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