The default typemap maps char ** to T_PACKEDARRAY. The input typemap for that looks like this:

T_PACKEDARRAY
    $var = XS_unpack_$ntype($arg)

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so to convert the perl argument to a char ** value it will call XS_unpackcharPtrPtr. However implementing this function is something you will need to do as xsubpp can't know what the meaning of the data is.

The following (untested) code might be useful if you want to pass an array reference from perl and your c code expects a NULL terminated list of strings:

char **
XS_unpack_charPtrPtr (SV *arg) {
    char **ret;
    AV *av;
    I32 i;

    if (!arg || !SvOK (arg) || !SvROK (arg) || (SvTYPE (SvRV (arg)) !=
+ SVt_AV)) {
        croak ("array reference expected");
    }

    av = (AV *)SvRV (arg);
    ret = (char **)malloc (av_len (av) + 1);

    for (i = 0; i <= av_len (av); i++) {
        SV **elem = av_fetch (av, i, 0);

        if (!elem || !*elem) {
            croak ("foo"):
        }

        ret[i] = SvPV_nolen (*elem);
    }

    ret[i + 1] = NULL;

    return ret;
}

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As this function allocates memory you will need to free the return value when you don't need it anymore. The CLEANUP section of an xsub might be a good place for that.

In reply to Re: char ** typemap in perlxs by rafl
in thread char ** typemap in perlxs by Temeschwarrior

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