form_fieldtype - define validation-field types
bool (* const field_check)(FIELD *, const void *),
bool (* const char_check)(int, const void *));
int free_fieldtype(FIELDTYPE *fieldtype);
void *(* const make_arg)(va_list *),
void *(* const copy_arg)(const void *),
void (* const free_arg)(void *));
bool (* const next_choice)(FIELD *, const void *),
bool (* const prev_choice)(FIELD *, const void *));
FIELDTYPE *link_fieldtype(FIELDTYPE *type1,
The function new_fieldtype creates a new field type usable
for data validation. You supply it with field_check, a
predicate to check the validity of an entered data string
whenever the user attempts to leave a field. 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.
You also supply new_fieldtype with char_check, a function
to validate input characters as they are entered; it will
be passed the character to be checked and a pointer to an
The function free_fieldtype frees the space allocated for
a given validation type.
The function set_fieldtype associates three storage-management
functions with a field type. The mak_arg function
is automatically applied to the list of arguments you give
set_field_type when attaching validation to a field; its
job is to bundle these into an allocated argument-block
object which can later be passed to validation predicated.
The other two hook arguments should copy and free argument-block
structures. They will be used by the formsdriver
code. You must supply the mak_arg function, the
other two are optional, you may supply NULL for them. In
this case it is assumed that mak_arg doesn't allocate memory
but simply loads the argument into a single scalar
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
The pointer-valued routines return NULL on error.
The integer-valued routines return one of the following
codes on error:
E_OK The routine succeeded.
E_SYSTEM_ERROR [Toc] [Back]
System error occurred (see errno).
E_BAD_ARGUMENT [Toc] [Back]
Routine detected an incorrect or out-of-range argument.
E_CONNECTED [Toc] [Back]
The field is already connected to a form.
The header file <form.h> automatically includes the header
All of the (char *) arguments of these functions should
actually be (void *). The type has been left uncorrected
for strict compatibility with System V.
These routines emulate the System V forms library. They
were not supported on Version 7 or BSD versions.
Juergen Pfeifer. Manual pages and adaptation for new
curses by Eric S. Raymond.
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