form_field_validation - data type validation for fields

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

       By default, no validation is done on form fields.  You can associate a form with a fieldtype, making the
       form library validate input.

   field_arg
       Returns  a pointer to the field's argument block.  The argumentblock is an opaque structure containing a
       copy of the arguments provided in a set_field_type call.

   field_type
       Returns a pointer to the fieldtype associated with the form field, i.e., by calling set_field_type.

   set_field_type
       The function set_field_type associates a field type with a given form field.  This is the type checked by
       validation functions.  Most field types are configurable, via arguments which the  caller  provides  when
       calling set_field_type.

       Several field types are predefined by the form library.

form_field_validation - data type validation for fields

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

       It  is  possible  to  set  up  new  programmer-defined  field types.  Field types are implemented via the
       FIELDTYPE data structure, which contains several pointers to functions.

       See the fieldtype(3FORM) manual page, which describes functions which can be used to construct  a  field-
       type dynamically.

       The predefined types are as follows:

   TYPE_ALNUM
       Alphanumeric data.  Required parameter:

       •   a third int argument, a minimum field width.

   TYPE_ALPHA
       Character data.  Required parameter:

       •   a third int argument, a minimum field width.

   TYPE_ENUM
       Accept one of a specified set of strings.  Required parameters:

       •   a third (char**) argument pointing to a string list;

       •   a fourth int flag argument to enable case-sensitivity;

       •   a  fifth  int flag argument specifying whether a partial match must be a unique one.  If this flag is
           off, a prefix matches the first of any set of more than one list elements with that prefix.

       The library copies the string list, so you may use a list that lives in automatic variables on the stack.

   TYPE_INTEGER
       Integer data, parsable to an integer by atoi(3).  Required parameters:

       •   a third int argument controlling the precision,

       •   a fourth long argument constraining minimum value,

       •   a fifth long constraining maximum value.  If the maximum value is less than or equal to  the  minimum
           value, the range is simply ignored.

       On  return,  the field buffer is formatted according to the printf format specification “.*ld”, where the
       “*” is replaced by the precision argument.

       For details of the precision handling see printf(3).

   TYPE_NUMERIC
       Numeric data (may have a decimal-point part).  Required parameters:

       •   a third int argument controlling the precision,

       •   a fourth double argument constraining minimum value,

       •   and a fifth double constraining maximum value.  If your system supports locales,  the  decimal  point
           character  must  be  the one specified by your locale.  If the maximum value is less than or equal to
           the minimum value, the range is simply ignored.

       On return, the field buffer is formatted according to the printf format specification  “.*f”,  where  the
       “*” is replaced by the precision argument.

       For details of the precision handling see printf(3).

   TYPE_REGEXP
       Regular expression data.  Required parameter:

       •   a  third argument, a regular expression (char*) string.  The data is valid if the regular expression
           matches it.

       Regular expressions are in the format of regcomp and regexec.

       The regular expression must match the whole field.  If you have for  example,  an  eight  character  wide
       field,  a  regular  expression  "^[0-9]*$"  always  means  that you have to fill all eight positions with
       digits.  If you want to allow fewer digits, you may use for  example  "^[0-9]*  *$"  which  is  good  for
       trailing  spaces  (up to an empty field), or "^ *[0-9]* *$" which is good for leading and trailing spaces
       around the digits.

   TYPE_IPV4
       An Internet Protocol Version 4 address.  Required parameter:

       •   none

       The form library checks whether or not the buffer has the form a.b.c.d, where a, b, c, and d are  numbers
       in the range 0 to 255.  Trailing blanks in the buffer are ignored.  The address itself is not validated.

       This is an ncurses extension; this field type may not be available in other curses implementations.

       The  functions field_type and field_arg return NULL on error.  The function set_field_type returns one of
       the following:

       E_OK The routine succeeded.

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

ncurses(3NCURSES), form(3FORM), fieldtype(3FORM), form_variables(3FORM)

ncurses 6.5                                        2025-02-15                            field_validation(3FORM)

#include<form.h>void*field_arg(constFIELD*field);FIELDTYPE*field_type(constFIELD*field);intset_field_type(FIELD*field,FIELDTYPE*type,...);/*predefinedfieldtypes*/FIELDTYPE*TYPE_ALNUM;FIELDTYPE*TYPE_ALPHA;FIELDTYPE*TYPE_ENUM;FIELDTYPE*TYPE_INTEGER;FIELDTYPE*TYPE_NUMERIC;FIELDTYPE*TYPE_REGEXP;FIELDTYPE*TYPE_IPV4;