H5P_GET_ELINK_PREFIX retrieves the prefix applied to the path of any external links traversed.
When an external link is traversed, the prefix is retrieved from the link access property list lapl_id, returned in the user-allocated buffer pointed to by prefix, and prepended to the filename stored in the external link.
The size in bytes of the prefix, including the NULL terminator, is specified in size. If size is unknown, a preliminary H5P_GET_ELINK_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.