Q155809: HOWTO: Use the SYS(3053) Function Handle with ODBC

Article: Q155809
Product(s): Microsoft FoxPro
Version(s): WINDOWS:2.5,5.0,6.0
Operating System(s): 
Keyword(s): kbinterop kbAutomation kbMDAC250
Last Modified: 22-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 6.0 
- Microsoft Data Access Components version 2.5 
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SUMMARY
=======

Visual FoxPro 5.0 introduces a new SYS() function, SYS(3053), which returns the
ODBC hEnv (environment handle) that Visual FoxPro uses for connectivity
operations. One of the uses of the SYS() function is to get a list of available
datasources that users can connect to.

MORE INFORMATION
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NOTE: Visual FoxPro uses the ODBC environment handle returned by SYS(3053) for
all of its connectivity operations. Use this handle for information retrieval,
not for changing options associated with it. In particular, you should not call
functions such as SQLFreeEnv(), which would release the handle while FoxPro was
using it and cause instability in the Visual FoxPro environment.

The SYS(3053) return value is called an hEnv, which is a handle used by ODBC to
describe an environment in which connectivity operations take place. One feature
not available natively in FoxPro is the ability to generate a list of
datasources on users' machines.

ODBC has an API function called SQLDataSources that you can use to provide this
functionality. SQLDataSources requires an hEnv--which you can get from the
SYS(3053) function--to be passed to it. The sample below uses the Visual FoxPro
DECLARE (DLL) function to register the SQLDataSources API, and then passes the
value returned from SYS(3053) to that API in order to retrieve the list of
datasources and descriptions.

    #DEFINE SQL_FETCH_NEXT 1
     #DEFINE SQL_FETCH_FIRST 2
     #DEFINE SQL_SUCCESS 0
     #DEFINE MAX_STRING 128

     DECLARE INTEGER SQLDataSources IN ODBC32.DLL ;
        INTEGER henv, SHORT fdirection, ;
        STRING @szDSN, INTEGER cbDSNMax, ;
        INTEGER @pcbDSN, STRING @szDescription, ;
        INTEGER cbDescriptionMax, INTEGER @pcbDescriptionn

     hEnv = VAL(SYS(3053))      && The hEnv (converted to a number)
     cbDsnMax = MAX_STRING      && How long can the DSN Name be?
     pcbDSN = 0                 && How many were actually returned
     cbDescriptMax = MAX_STRING && How long can the description be?
     pcbDescript = 0            && How long the description actually was

     fDirection = SQL_FETCH_FIRST     && The first time start at the top
     retVal = SQL_SUCCESS             && Start with no errors
     DO WHILE (retVal = SQL_SUCCESS)
        szDsn = SPACE(MAX_STRING+1)   && Make sure there is enough space
        szDescript = SPACE(MAX_STRING+1)

        retval = SQLDataSources(hEnv, fDirection, ;
                       @szDSN, cbDSNMax, @pcbDSN, ;
                       @szDescript, cbDescriptMax, @pcbDescript)
        ? LEFT(szDSN, pcbDSN)
        ? LEFT(szDescript, pcbDescript)

        * We only want to do the SQL_FETCH_FIRST the first time
        fDirection = SQL_FETCH_NEXT
     ENDDO

Additional query words:

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Keywords          : kbinterop kbAutomation kbMDAC250 
Technology        : kbVFPsearch kbAudDeveloper kbMDACSearch kbMDAC250 kbVFP500 kbVFP600
Version           : WINDOWS:2.5,5.0,6.0
Issue type        : kbhowto

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