Both data conversion functions are required for each field type or form processing will fail.
If appropriate, you can use the data conversion functions provided by the system. If you are adding a field type that is an extension of an existing field type, you might find it easier to call one of the system data conversion functions from your own and just add code for the additional processing.
The system data conversion functions are listed in the Function Reference in the categorical listing section of the manual. All the names of the data-to-string conversion functions begin with "dc_fr." All the names of the string-to-data begin with "dc_to." Refer to their function reference pages for details about the actions taken by the system functions.
Specifications for Data Conversion Functions
Writing Data Variable to String Conversion Functions
Writing String to Data Variable Conversion Functions
