H5P_GET_VIRTUAL_PREFIX retrieves the prefix applied to the path of any VDS source files traversed.
When an VDS source file is traversed, the prefix is retrieved from the dataset access property list dapl_id, returned in the user-allocated buffer pointed to by prefix, and prepended to the filename stored in the VDS virtual file, set with H5P_SET_VIRTUAL.
The size in bytes of the prefix, including the NULL terminator, is specified in size. If size is unknown, a preliminary H5P_GET_VIRTUAL_PREFIX call with the pointer prefix set to NULL will return the size of the prefix without the NULL terminator.
If successful, returns a non-negative value specifying the size in bytes of the prefix without the NULL terminator; otherwise returns a negative value.