# form_field_validation

## NAME



           **form_field_validation** - data type validation for fields
    


## SYNOPSIS



           **#include <form.h>**
    
           **void *field_arg(const FIELD ***_field_**);**
           **FIELDTYPE *field_type(const FIELD ***_field_**);**
           **int set_field_type(FIELD ***_field_**, FIELDTYPE ***_type_**, ...);**
    
           /* predefined field types */
           **FIELDTYPE *TYPE_ALNUM;**
           **FIELDTYPE *TYPE_ALPHA;**
           **FIELDTYPE *TYPE_ENUM;**
           **FIELDTYPE *TYPE_INTEGER;**
           **FIELDTYPE *TYPE_NUMERIC;**
           **FIELDTYPE *TYPE_REGEXP;**
           **FIELDTYPE *TYPE_IPV4;**
    


## DESCRIPTION



           By default, no validation is done on form fields.  You can
           associate a form with with a _field type_ , making the form library
           validate input.
    
       **field_arg**
           Returns a pointer to the field's argument block.  The _argument_
           _block_ is an opaque structure containing a copy of the arguments
           provided in a **set_field_type** call.
    
       **field_type**
           Returns a pointer to the _field type_ 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.
    
       **Predefined types**
           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 **form_fieldtype**(3X) 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.
    


## RETURN VALUE



           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)).
    


## NOTES



           The header file **< form.h> **automatically includes the header file
           **< curses.h>**.
    


## PORTABILITY



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


* * *