form_fieldtype - define validation-field types

       Juergen Pfeifer.  Manual pages and adaptation for new curses by Eric S. Raymond.

new_fieldtype
       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.

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

   set_fieldtype_arg
       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.

   set_fieldtype_choice
       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.

   link_fieldtype
       The  function  link_fieldtype creates a new field type from the two given types.  They are connected by a
       logical “or”.

form_fieldtype - define validation-field types

       These routines emulate the System V forms library.  They were not supported on Version 7 or BSD versions.

       The pointer-valued routines return NULL on error.  They set errno according to their success:

       E_OK The routine succeeded.

       E_BAD_ARGUMENT
            Routine detected an incorrect or out-of-range argument.

       E_SYSTEM_ERROR
            System error occurred, e.g., malloc failure.

       The integer-valued routines return one of the following codes on error:

       E_OK The routine succeeded.

       E_BAD_ARGUMENT
            Routine detected an incorrect or out-of-range argument.

       E_CONNECTED
            The field is already connected to a form.

       E_CURRENT
            The field is the current field.

       E_SYSTEM_ERROR
            System error occurred (see errno(3)).

ncurses(3NCURSES), form(3FORM), field_validation(3FORM)

ncurses 6.5                                        2025-01-18                                   fieldtype(3FORM)

#include<form.h>FIELDTYPE*new_fieldtype(bool(*constfield_check)(FIELD*,constvoid*),bool(*constchar_check)(int,constvoid*));intfree_fieldtype(FIELDTYPE*fieldtype);intset_fieldtype_arg(FIELDTYPE*fieldtype,void*(*constmake_arg)(va_list*),void*(*constcopy_arg)(constvoid*),void(*constfree_arg)(void*));intset_fieldtype_choice(FIELDTYPE*fieldtype,bool(*constnext_choice)(FIELD*,constvoid*),bool(*constprev_choice)(FIELD*,constvoid*));FIELDTYPE*link_fieldtype(FIELDTYPE*type1,FIELDTYPE*type2);