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<H2><A NAME="SECTION02448000000000000000"></A>
<A NAME="3083"></A><A NAME="3084"></A>
<BR>
The C Data Structure
</H2>
<P>
If even the macro interface is not fast enough for you,
you can access the internal data structure for all the basic types except string.
You cannot access the internal data structure for arrays of strings,
interfaces and objects.
<P>
The basic form of the C data structure for type XXXX is:
<P>
<BR>
<PRE CLASS="verbatim">struct sidl__array_vtable {
/* Release resources associted with the array (refcount at zero) */
void (*d_destroy)(struct sidl__array *);
/* Clone or addRef depending on whether data is borrowed */
struct sidl__array *(*d_smartcopy)(struct sidl__array *);
/* Return the type of the array. */
int32_t (*d_arraytype)(void);
};
struct sidl__array {
int32_t *d_lower;
int32_t *d_upper;
int32_t *d_stride;
const struct sidl__array_vtable *d_vtable;
int32_t d_dimen;
int32_t d_refcount;
};
struct sidl_XXXX__array {
struct sidl__array d_metadata;
<value type for XXXX> *d_firstElement;
};
</PRE></td></tr></table></blockquote>
<P>
The string ``<SPAN CLASS="MATH"><IMG
WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img7.png"
ALT="$<$"></SPAN>value type for XXXX<SPAN CLASS="MATH"><IMG
WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img8.png"
ALT="$>$"></SPAN>'' should be replaced by something like
<TT>sidl_bool</TT>for an array of <TT><I CLASS="slanted">bool</I></TT>,
<TT>int32_t</TT> for any array of <TT><I CLASS="slanted">int</I></TT>,
<TT>double</TT> for an array of <TT><I CLASS="slanted">double</I></TT>,
<TT>int64_t</TT> for an array of <TT><I CLASS="slanted">long</I></TT>, etc. (See Table <A HREF="node65.html#tbl:basics:arraytypes">5.2</A>)
<P>
<DL>
<DT><STRONG><TT>d_dimen</TT></STRONG></DT>
<DD>tells the dimension of the multi-dimensional array.
<TT>d_lower</TT>, <TT>d_upper</TT>, and <TT>d_stride</TT> each point to arrays
of <TT>d_dimen int32_t</TT>'s. <TT>d_lower[i]</TT> provides the lower bound
for the index in dimension <TT>i</TT>, and <TT>d_upper[i]</TT> provides the upper
bound for the index in dimension <TT>i</TT>. Both the lower and upper bounds
are valid index values; the upper bound is not one past the end.
<P>
</DD>
<DT><STRONG><TT>d_borrowed</TT></STRONG></DT>
<DD>is true if the array does not managed the data
that <TT>d_firstElement</TT> points too, and it is false otherwise. This
mainly influences the behavior of the destructor.
<P>
Clients should not modify <TT>d_lower</TT>, <TT>d_upper</TT>, <TT>d_stride</TT>,
<TT>d_dimen</TT>, <TT>d_borrowed</TT> or (in the case of pointers) the values
to which they point.
<P>
</DD>
<DT><STRONG><TT>d_stride[i]</TT></STRONG></DT>
<DD>determines how elements are packed in dimension
<TT>i</TT>. A value of 1 means that to get from element <TT>j</TT> to <TT>j+1</TT>
in dimension <TT>i</TT>, you add one to the data pointer. Negative values for
<TT>d_stride</TT> can be used to express a transposed matrix. The definition
also allows either column or row major ordering for the data, and it also
allows treating a subsection of an array as an array.
<P>
</DD>
</DL>
<P>
The data structure was inspired by the data structure used by Numeric Python;
although, in Numeric Python, the stride is in terms of bytes. In SIDL, the
stride is in terms of number of objects. One can convert to the Numeric
Python view of things by multiplying the stride by the sizeof the value type.
<P>
<P>
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