LFind
LFind Obtain the address and length of a cell's data void LFind(offset, len, theCell, theList ); short *offset ; receives offset from start of list data
short *len ; receives length of cell data
Cell theCell ; cell to query ListHandle theList ; handle leading to a ListRec LFind is an alternative to LGetCell. It obtains the length of a cell's contents and a value you can use to calculate the address of that data.
offset is the address of a short integer. Upon return, it contains the offset
from the start of the data area of theList at which a cell's data may be
found (or -1 if theCell is invalid). Using this value requires
quadruple in direction (see the examples, below).
len is the address of a short integer; upon return, it contains the length
of the data associated with theCell (or -1 if theCell is invalid).
theCell specifies the cell whose data you wish to access.
theList is a handle leading to a variable-length ListRec structure. It is a value previously obtained via LNew.
Notes: The data area of a list is identified by a handle stored in the cells field of
the ListRec. That handle leads to an un structured array, no larger than 32K, containing the cell contents in no special order.
Here's a version of the code you can use to access the data:
DataHandle dh; [TOKEN:12074] defined in Lists.h */
DataPtr dp;
char *cp;
short offset, len;
LFind( &offset, &len, theCell, theList ); if ( offset == -1 ) {/* . . . bad value in theCell , otherwise. . . */}
dh = (* theList)->cells; [TOKEN:12074] get the handle */
dp = *dh; [TOKEN:12074] address of start of data area */
cp = (char *) dp; [TOKEN:12074] coerce to char * */
cp += offset; [TOKEN:12074] now cp points to data of theCell
*/
if (*cp == 'X' ) { /*... etc ...*/ } /* compare, examine, print, etc.*/
Here's the terse version of the final 5 lines above:
cp = ( **(* theList)->cells ) + offset;
if ( *cp == 'X' ) {... etc ...} /* compare, examine, etc.*/
If you just want to draw the text, you can use the following:
DrawText( **(* theList)->cells, offset, length ); Note: the entire list data area can move around unless you lock it down;
e.g.,
HLock( (* theList)->cells ); Furthermore, the storage for any individual cell can be moved around
Therefore: LFind should NOT be used to pre-calculate pointers to cell data; the only safe time to use such cell data addresses is directly after calling
The LGetCell function may be easier to use. But since it copies cell data to a local buffer, it is inevitably slower than examining the data directly.