type: The type of the data. Must be one of the constants (defined in
SDDS.h) SDDS_LONGDOUBLE, SDDS_DOUBLE, SDDS_FLOAT, SDDS_LONG,
SDDS_ULONG, SDDS_SHORT, SDDS_USHORT, or SDDS_CHARACTER.
data: The reference address of the data to be converted.
index: The offset of the address of the item to be converted from the reference address,
in units of the size of the declared type.
return value: The double precision value is returned. If an error occurs, zero is returned and an error message is
recorded.