Manpages - form_fieldtype.3x

The function new_fieldtype creates a new field type usable for data validation. Its parameters are function pointers:

field_check

This function checks the validity of an entered data string whenever the user attempts to leave a field. It has two arguments:

• The (FIELD *) argument is passed in so the validation predicate can see the field’s buffer, sizes and other attributes.
• The second argument is an argument-block structure, about which more below.

char_check

This function validates input characters as they are entered. The form library passes it the character to be checked and a pointer to an argument-block structure.

The free_fieldtype function frees the space allocated for a given validation type by new_fieldtype.

The function set_fieldtype_arg associates three storage-management functions with a field type:

make_arg

This function is automatically applied to the list of arguments you give set_field_type when attaching validation to a field. It stores the arguments in an allocated argument-block object which is used when validating input.

copy_arg

This function may be used by applications to copy argument-blocks.

free_arg

Frees an argument-block structure.

You must supply the make_arg function. The other two are optional: you may supply NULL for them. In this case, the form library assumes that make_arg does not allocate memory but simply loads the argument into a single scalar value.

The form driver requests REQ_NEXT_CHOICE and REQ_PREV_CHOICE assume that the possible values of a field form an ordered set, and provide the forms user with a way to move through the set.

The set_fieldtype_choice function allows forms programmers to define successor and predecessor functions for the field type. These functions take the field pointer and an argument-block structure as arguments.

The function link_fieldtype creates a new field type from the two given types. They are connected by an logical ’OR’.