Declaring an External Blob Filter to the Database

From InterBase

Go Up to Filtering Blob Data

To declare an external filter to a database, use the DECLARE FILTER statement. For example, the following statement declares the filter, SAMPLE:

ENTRY POINT 'FilterFunction'
MODULE_NAME 'filter.dll';

In the example, the input subtype of the filter is defined as –1 and its output subtype as
–2. If subtype –1 specifies lowercase text, and subtype –2 uppercase text, then the purpose of filter SAMPLE would be to translate Blob data from lowercase text to uppercase text.

The ENTRY_POINT and MODULE_NAME parameters specify the external routine that InterBase calls when the filter is invoked. The MODULE_NAME parameter specifies filter.dll, the dynamic link library containing the executable code of the filter. The ENTRY_POINT parameter specifies the entry point into the DLL. Although the example shows only a simple file name, it is good practice to specify a fully-qualified path name, since users of your application need to load the file.

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