Dynamic Data Exchange and XlTable Format by malj


									Dynamic Data Exchange and XlTable Format

Microsoft Windows provides several methods for transferring data between applications.
One way to transfer data is to use Windows dynamic data exchange (DDE). DDE is a
message protocol for data exchange between Windows programs. It allows software
developers to design applications that share data and thereby provide the user with a more
integrated Windows environment.

For complete information about DDE, see the documentation for the Microsoft Windows
Software Development Kit (SDK). This article describes the DDE formats that Microsoft
Excel supports, and it provides detailed information about the high-performance XlTable
DDE format.

DDE Formats

Microsoft Excel supports several DDE formats. The formats are listed in the following
table in the order of precedence defined by Microsoft Excel, from highest precedence
(XlTable) to lowest precedence (CF_METAFILEPICT). Clipboard formats that begin
with CF_ are formats that are already defined in Windows.h. Clipboard formats without
CF_ must be registered before use. For more information about registering formats, see
Registering Clipboard Formats.

  Clipboard format                                        Description

  XlTable                                                 Microsoft Excel fast table format. For more information, see Fast Table Format.

  Biff5                                                   Binary interchange file format (BIFF) for Microsoft Excel version 5.0. For more information about the fil

  Biff4                                                   Binary interchange file format (BIFF) for Microsoft Excel version 4.0.

  Biff3                                                   BIFF for Microsoft Excel version 3.0.

  Biff                                                    BIFF for Microsoft Excel version 2.x.

  CF_SYLK                                                 Microsoft symbolic link (SYLK) format. Microsoft Excel for the Apple Macintosh was originally designe
                                                          now supported by Microsoft Excel on both the Windows and Macintosh platforms.

  Wk1                                                     Lotus® 1-2-3® Release 2.01 and Release 2.2 format.

  Csv                                                     Comma-separated values format, commonly used in BASIC language I/O. This is similar to CF_TEXT fo
                                                          separate fields.

  CF_TEXT                                                 The simplest form of Clipboard data. It is a null-terminated string containing a carriage return and linefee

  Rich Text Format                                        A method of encoding formatted text and graphics for easy transfer between applications. Rich Text Form
                                                          processing programs such as Microsoft Word for Windows and Microsoft Word for the Macintosh.

  CF_DIF                                                  An ASCII format used by the VisiCalc™ spreadsheet program. The format is under the control of Lotus D

  CF_BITMAP                                               A Windows version 2.x-compatible bitmap.

  CF_METAFILEPICT                                         A metafile picture structure. For complete information, see the documentation for the Microsoft Windows
Registering Clipboard Formats

Whenever an application uses a private Clipboard format — such as XlTable, Biff5,
Biff4, Biff3, Biff, Wk1, Csv, or Rich Text Format — it must register the format before
using it. Microsoft Excel registers these private Clipboard formats, and your DDE
application must also register any of these formats that you want to use to exchange data.

For example, to register XlTable, use the following Windows API function call.

wCBformat = RegisterClipboardFormat((LPSTR)"XlTable");

If the function call is successful, the return value is equal to the format value for the
XlTable format. This format value (type WORD) is between 0xC000 and 0xFFFF, and
it's equal to the format value that Windows returned to Microsoft Excel when it registered
XlTable. If Windows cannot register XlTable, the function returns 0 (zero).

Fast Table Format

The fast table format, XlTable, is designed to maximize the DDE transfer speed of
Microsoft Excel. XlTable consists of a sequence of data blocks that represent a
rectangular selection of cells (a table). Each data block has three parts:

WORD tdt       /* the table data type */
WORD cb       /* the size (count of bytes) of the data */
BYTE data[cb] /* the data */

The first data block is always of type tdtTable, which specifies the number of rows and
the number of columns in the table. The data blocks that follow tdtTable represent all the
cells in the table. Microsoft Excel renders the reference of the cells in the table (for
example, R1C1:R2C4) as the item part of the DDE message.

The cells are always rendered row-wise. In other words, all the cells in the first row of the
table appear first, then all the cells in the second row, and so on. To minimize overhead,
adjacent cells of the same type (tdt) are represented together in one data block, even if the
cells are in different rows. In other words, one tdtFloat can contain several numbers, one
tdtString can contain several strings, one tdtBool can contain several Boolean values, and
so on. For examples, see the following sections, "XlTable Example 1" and "XlTable
Example 2."

The data block types are described in the following table.

  Data block type             Value                          Description

  tdtTable                    0x0010                         The size of the table. The data (4 bytes, cb=4) consists of two words. The first word is the number of row

  tdtFloat                    0x0001                         IEEE-format floating-point number. The size of the number is 8 bytes per cell.

  tdtString                   0x0002                         String in st (byte-counted) format. The first byte contains the length of the string (cch). The string isn't n

  tdtBool                     0x0003                         Boolean value: 1 = TRUE

                                                             0 = FALSE

                                                             The length of the data is 2 bytes per cell.
  tdtError                     0x0004                       Error value: 0 = #NULL!

                                                            7 = #DIV/0!

                                                            15 = #VALUE!

                                                            23 = #REF!

                                                            29 = #NAME?

                                                            36 = #NUM!

                                                            42 = #N/A

                                                            The length of the data is 2 bytes per cell.

  tdtBlank                     0x0005                       A count of the number of consecutive undefined (blank) cells. The data (2 bytes, cb=2) contains the num

  tdtInt                       0x0006                       Unsigned integer. The length of the data is 2 bytes per cell. Microsoft Excel can read a number in this fo

  tdtSkip                      0x0007                       Number of cells to skip. A skipped cell is a cell that retains its previous value. In other words, a skipped
                                                            message. You can use tdtSkip to increase DDE performance if your application changes only one or two
                                                            Microsoft Excel doesn't support tdtSkip when the new cell data is part of a WM_DDE_POKE message.

XlTable Example 1

The following selection of three cells . . .

A1 East

A2 West

A3 North

. . . produces the XlTable rendering shown in the following table.

  Data (hexadecimal)                                          Description

  10 00 04 00 01 00 03 00                                     tdtTable, cb=4, rows=1, columns=3

  02 00 10 00                                                 tdtString, cb=16

  04 45 61 73 74                                              cch=4, East (tdtString continued)

  04 57 65 73 74                                              cch=4, West (tdtString continued)

  05 4e 6f 72 74 68                                           cch=5, North (tdtString continued)
Notice that the table contains three cells, but the XlTable rendering contains only one
tdtString data block.

XlTable Example 2

The XlTable format uses the tdtBlank data block to represent blank cells in a table. A
sequence of several blank cells may be represented by a single tdtBlank data block.

For example, the following table . . .

A1: 2   A2: 3

B1: 4 B2: 5

D1: 6   D2: 7

. . . produces the following XlTable rendering.

  Data (hexadecimal)                           Description

  10 00 04 00 02 00 04 00                      tdtTable, cb=4, rows=4, columns=2

  06 00 08 00 02 00 03 00 04 00 05 00          tdtInt, cb=8, int[0]=2, int[1]=3, int[2]=4, int[3]=5 (Microsoft Excel can read tdtInt as a client, but it would write tdtFl

  05 00 02 00 02 00                            tdtBlank, cb=2, data=2 (two cells are blank)

  06 00 04 00 06 00 08 00                      tdtInt, cb=4, int[0]=6, int[1]=8

Biff5, Biff4, Biff3, and Biff Formats

The Biff5, Biff4, Biff3, and Biff Clipboard formats contain a variable number of records.
The records are identical to the corresponding records in the BIFF file. For more
information about the BIFF5 records, see Microsoft Excel File Format. The Biff4, Biff3,
and Biff formats are available for backward compatibility with existing applications. The
Biff Clipboard format corresponds to the BIFF2 file format.

If you implement one of the BIFF Clipboard formats, your code should be prepared to
receive all BIFF records except file-specific records such as the following:










The requisite BIFF records that your code must provide when it writes to the Clipboard
are as follows:


Cell record or records (BLANK, BOOLERR, and so on

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