How To Use the SYS(3053) Function Handle with ODBC

• Microsoft Visual FoxPro for Windows, version 5.0

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

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

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

   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