SystemCallError.new

static VALUE
syserr_initialize(int argc, VALUE *argv, VALUE self)
{
#if !defined(_WIN32)
    char *strerror();
#endif
    const char *err;
    VALUE mesg, error, func, errmsg;
    VALUE klass = rb_obj_class(self);

    if (klass == rb_eSystemCallError) {
        st_data_t data = (st_data_t)klass;
        rb_scan_args(argc, argv, "12", &mesg, &error, &func);
        if (argc == 1 && FIXNUM_P(mesg)) {
            error = mesg; mesg = Qnil;
        }
        if (!NIL_P(error) && st_lookup(syserr_tbl, NUM2LONG(error), &data)) {
            klass = (VALUE)data;
            /* change class */
            if (!RB_TYPE_P(self, T_OBJECT)) { /* insurance to avoid type crash */
                rb_raise(rb_eTypeError, "invalid instance type");
            }
            RBASIC_SET_CLASS(self, klass);
        }
    }
    else {
        rb_scan_args(argc, argv, "02", &mesg, &func);
        error = rb_const_get(klass, id_Errno);
    }
    if (!NIL_P(error)) err = strerror(NUM2INT(error));
    else err = "unknown error";

    errmsg = rb_enc_str_new_cstr(err, rb_locale_encoding());
    if (!NIL_P(mesg)) {
        VALUE str = StringValue(mesg);

        if (!NIL_P(func)) rb_str_catf(errmsg, " @ %"PRIsVALUE, func);
        rb_str_catf(errmsg, " - %"PRIsVALUE, str);
    }
    mesg = errmsg;

    rb_call_super(1, &mesg);
    rb_ivar_set(self, id_errno, error);
    return self;
}