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Q110472: INF: How to Differentiate Multiple SQLAllocEnv() Calls

Article: Q110472
Product(s): Open Database Connectivity (ODBC)
Version(s): WINDOWS:1.0
Operating System(s): 
Keyword(s): 
Last Modified: 29-DEC-1999

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The information in this article applies to:

- Microsoft Open Database Connectivity, version 1.0 
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SUMMARY
=======

In version 1.0 of Open Database Connectivity (ODBC), every time an application
calls SQLConnect(), the Driver Manager calls the Driver's SQLAllocEnv(),
SQLAllocConnect(), and SQLConnect() functions in succession. This means that an
ODBC driver can be called to allocate multiple environments for the same
application.

Since a driver must allocate only one environment per application, it must be
able to distinguish between the first call to SQLAllocEnv from an application
and subsequent calls to SQLAllocEnv()

MORE INFORMATION
================

Since only one environment should be allocated for an ODBC application by the
driver, even though multiple calls to SQLAllocEnv are made from the Driver
Manager, a driver can use the Windows function GetCurrentTask() to determine
whether an environment has already been allocated for the calling application
(task).

Typically, a driver can build a list of tasks that currently have the
environments allocated, and on every call to SQLAllocEnv(), the driver can use
this list to determine if the current task has an allocated environment. If the
task is found in this list, the driver can return the previously allocated
environment associated with that task, without having to allocate a new
environment.

Drivers written to the ODBC version 2.0 specification need not use the above
mechanism because the 2.0 Driver Manager does not call SQLAllocEnv() in the
Driver on every SQLConnect(). Thus, an ODBC 2.0 driver is assured that its
SQLAllocEnv() will be called only once on the first SQLConnect() from the
application. Subsequent SQLConnect() calls in the application to that driver
will not result in SQLAllocEnv() calls into the driver.

Additional query words:

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Keywords          :  
Technology        : kbAudDeveloper kbODBCSearch kbODBC100
Version           : WINDOWS:1.0

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