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setting is (in bytes). A likely problem and its solution Here's one caveat to observe: the SET(`BLOCKSIZE') function always returns the current block size setting in bytes. If, for example, you SET BLOCKSIZE TO 1, SET('BLOCKSIZE') will return 512. If you're changing the block size in a routine and want to preserve and restore the caller's block size (a technique often used in application startup and shutdown code as well), you run into a problem. Consider the following code: nOldBlockSize = SET('BLOCKSIZE') SET BLOCKSIZE TO 64 * more code here, then reset the caller's block size SET BLOCKSIZE TO (nOldBlockSize) If the caller had previously SET BLOCKSIZE TO 0, then SET('BLOCKSIZE') will return a value of 1, since SET BLOCKSIZE TO 0 produces one-byte blocks. But when you "restore" the caller's block size, you'll issue SET BLOCKSIZE TO 1, which will create 512-byte blocks, just like in the good old days of dBASE III Plus! To get around this problem, you need code like the following instead: nOldBlockSize = SET('BLOCKSIZE') IF nOldBlockSize = 1 nOldBlockSize = 0 ENDIF SET BLOCKSIZE TO 64 * more code here, then reset the caller's block size SET BLOCKSIZE TO (nOldBlockSize) REPLACE and fragmentation A technique you can use to minimize .FPT fragmentation regardless of memo block size is to avoid repeated REPLACEs on a memo field whenever possible. For example, suppose that you have code that appends transaction log information to a memo field named TranLog. Perhaps you need to add several lines to the field. You might have code similar to the following: FOR n = 1 TO nMessages REPLACE TranLog WITH CHR(13) + cTransMsg[n] ADDITIVE ENDFOR This code extends the memo field on each iteration of the loop, potentially orphaning .FTP file space each time. It's much better, and probably faster, to build the additional data in memory and
do a single REPLACE: cNewMessages = '' FOR n = 1 TO nMessages cNewMessages = cNewMessages + CHR(13) + cTransMsg[n] ENDFOR IF NOT EMPTY(cNewMessages) REPLACE TranLog WITH cNewMessages ADDITIVE ENDIF I once had a text management application that would read in text files, do on-the-fly translations, and write the text files a line at a time to a memo field. I noticed that the memo file was bloating by a factor of several hundred K per day, even though no new records were being added to the table. This coding trick got rid of most of the "bloat." Conclusion Fiddling with memo block sizes isn't one of the most pressing issues in FoxPro database development, but as you deal with larger and larger databases, some attention to detail in this area can have a significant impact on disk storage efficiency. And, as you saw in the code examples I just shared, paying attention to the subtleties of syntax can produce big savings, too. Finally, I suspect that Visual FoxPro is taking us in directions that are likely to cause us to provide database administration services to clients in addition to application design and development services. Knowing how to tune memo fields is one skill that will differentiate the kind of administration you can provide from what the client can do in-house. Bob Grommes is editor of <strong>FoxTalk</strong> and president of Software Excellence in Kalamazoo, Michigan. CompuServe 74126,72. Ease Form Design Tasks with SUPERCLASS Whil Hentzen (4) GENSCRNX fans probably wonder what Ken Levy has been up to since the release of Visual FoxPro. Wonder no more: he's produced another "must have" that every Visual FoxPro developer will want in his bag of tricks. Ever had one of those days? The type of day where nothing goes right? You're working in Visual FoxProand you have to look at the Language Reference for just about every command you type. For some reason, you can't remember the syntax for even the simplest commands, like WAIT WINDOW or SKIP. You even tried to do some simple data entry in a Browse window, but couldn't figure out why Ctrl-N wasn't working when you were adding new records.
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Page 27 and 28: a record in the .SCX. Two fields in
Page 29 and 30: A Glossary of Object-Oriented Termi
Page 31 and 32: Encapsulation Ecapsulation is the c
Page 33 and 34: Memo fields (variable-length fields
Page 35: (VCXs), regardless of what you curr
Page 39 and 40: change the superclass method, those
Page 41 and 42: Tabbed interfaces, such as those im
Page 43 and 44: * Initialize the variable for the c
Page 45 and 46: The first key to making everything
Page 47 and 48: when the button is disabled. The Sc
Page 49 and 50: *:SPRDRV6 NO_READ Here's the GENSCR
Page 51: Fox World News Micromega Systems ha

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