DOCUMENT:Q135905 25-MAY-2000 [foxpro] TITLE :How to Retrieve Records That Were Previously Zapped PRODUCT :Microsoft FoxPro PROD/VER:MS-DOS:2.0,2.5,2.5a,2.5b,2.6,2.6a; WINDOWS:2.5,2.5a,2.5b,2.6,2.6a,3.0 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual FoxPro for Windows, version 3.0 - Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a, 2.5b, 2.6, 2.6a - Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a ------------------------------------------------------------------------------- SUMMARY ======= Sometimes, Microsoft Visual FoxPro's ZAP command can be reversed and you can retrieve all the records by using a low-level file I/O. This method works only if the data was not overwritten by other files. The approximate number of records to retrieve is also important. MORE INFORMATION ================ Step-by-Step Example -------------------- 1. Open a program file named Lowlevel.prg and type in the following function: FUNCTION UNZAP PARAMETER Y IF Y>0 .AND. USED() IF RECCOUNT()=0 FILENAME=DBF() USE HANDLE=FOPEN(FILENAME,2) IF HANDLE>0 BYTE=FREAD(HANDLE,32) BKUP_BYTE=BYTE FIELD_SIZE=ASC(SUBSTR(BYTE,11,1))+(ASC(SUBSTR(BYTE,12,1))*256) FILE_SIZE=FSEEK(HANDLE,0,2) BYTE8=CHR(INT(Y/(256*256*256))) BYTE7=CHR(INT(Y/(256*256))) BYTE6=CHR(INT(Y/256)-IIF(Y/256>256,(INT(INT(Y/256)/256)*256),0)) BYTE5=CHR(MOD(Y,256)) BYTE=SUBSTR(BYTE,1,4)+BYTE5+BYTE6+BYTE7+BYTE8+SUBSTR(BYTE,9) =FSEEK(HANDLE,0) =FWRITE(HANDLE,BYTE) =FCHSIZE(HANDLE,FILE_SIZE+(FIELD_SIZE*Y)) =FCLOSE(HANDLE) ENDIF USE &FILENAME ENDIF ENDIF 2. Save and close the Lowlevel.prg program file. 3. Back up the table that you are going to experiment on to protect against data corruption. 4. Test the function by zapping the back-up of the table and then use the UNZAP function to retrieve the records. The following example uses the Foxuser.dbf table: a. In the Command window, type: SET PROCEDURE TO LOWLEVEL.PRG SET RESOURCE OFF USE FOXUSER b. Note how many records are in the foxuser file. For this example, assume that there are 50 records. c. In the Command window, type: ZAP =UNZAP(50) d. Note that all of the records are retrieved. 5. It is possible to use UNZAP to retrieve more records than what actually existed, especially if you do not know exactly how many records to retrieve. After you use UNZAP, you should browse the table to make sure only valid records were retrieved. Invalid records will immediately be apparent by the incomprehensible data in all the fields. Locate the last valid record and repeat step 4(c) and use the correct number of records. 6. If the Foxuser.dbf table is corrupt, delete the file. FoxPro will create a new one. Additional query words: VFoxWin FoxWin FoxDos ====================================================================== Keywords : Technology : kbVFPsearch kbAudDeveloper kbFoxproSearch kbZNotKeyword3 kbFoxPro200DOS kbFoxPro250DOS kbFoxPro250aDOS kbFoxPro250bDOS kbFoxPro260DOS kbFoxPro260aDOS kbFoxPro260 kbFoxPro250 kbFoxPro250a kbFoxPro250b kbFoxPro260a kbVFP300 Version : MS-DOS:2.0,2.5,2.5a,2.5b,2.6,2.6a; WINDOWS:2.5,2.5a,2.5b,2.6,2.6a,3.0 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2000.