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CDTDocV8

PropAddAsExtBuffer

The PropAddAsExtBuffer function adds a PowerDoc property to the PowerDoc object obj. This function is very similar to and compatible with PropAdd, which means that properties created by this function can be used in much the same capacity as if they were created by PropAdd. However, unlike PropAdd which copies the property value to a buffer that is managed by D-Type Power Engine, this function does not, meaning that the value remains in an external buffer that is under exclusive control of the application. Since the property value resides in this external buffer (i.e. outside the associated Power Engine document), the newly added property occupies a very small amount of storage space in the object obj (only the amount it takes to store the pointer and length of the external buffer).

PropAddAsExtBuffer is a specialized and advanced function that should be used only by applications that wish to store very large property values (e.g. large arrays or bitmap images) outside the associated Power Engine document and perform their own run-time memory management of large blocks of data. In all other cases PropAdd should be used instead.

Parameters

ParameterDescription

obj

Object's index in the Power Engine document.

name

A numerical value that identifies the property to be added. Can be a user-defined value or one of the predefined PowerDoc values. For a list of predefined name values, see the PropAdd function.

extbuffer

Pointer to an external buffer that holds the value of the property. Within the buffer, the value must be stored as native binary data (i.e. in the same format as if it was created by calling MakeBinary). Once this pointer is passed to PropAddAsExtBuffer, the location of the buffer cannot change. The buffer can be destroyed or reallocated only after the property has been removed from the object. Your application is responsible for managing and destroying the buffer. If this is not done properly, you could experience crashes, memory leaks and other similar problems.

extlen

Length of the binary data within the buffer, in bytes. Must not be negative. Although your application is allowed to change the value of the property (i.e. contents of the external buffer) at any time, its length must always remain precisely extlen bytes. Otherwise, you could experience crashes, memory access violations and other unexpected problems.

Return Value

See PropAdd.

Note

PowerDoc documents that contain properties created by this function should not be saved to disk by calling SaveToStream and later opened by calling AppendFromStream unless you are certain that the location of the buffer extbuffer will never change. If extbuffer changes after the document is saved and before it is opened again, you could experience crashes, memory access violations and similar problems.

Comments

See PropAdd.



 

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