form_fieldtype(3X)

💖 form_fieldtype(3X) 💖

okay bestie, so this is the form_fieldtype page from the ncurses library — it's literally all about crafting your own custom validation types for form fields, and it's giving main character energy fr fr ✨

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🌸 NAME 🌸

form_fieldtype — define validation-field types (yes, that's the whole vibe, we're building custom field types 💅)

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🎀 SYNOPSIS 🎀

#include <form.h>

FIELDTYPE *new_fieldtype(
    bool (* const field_check)(FIELD *, const void *),
    bool (* const char_check)(int, const void *));
int free_fieldtype(FIELDTYPE *fieldtype);

int set_fieldtype_arg(
    FIELDTYPE *fieldtype,
    void *(* const make_arg)(va_list *),
    void *(* const copy_arg)(const void *),
    void  (* const free_arg)(void *));
int set_fieldtype_choice(
    FIELDTYPE *fieldtype,
    bool (* const next_choice)(FIELD *, const void *),
    bool (* const prev_choice)(FIELD *, const void *));

FIELDTYPE *link_fieldtype(FIELDTYPE *type1,
                          FIELDTYPE *type2);

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🦋 DESCRIPTION 🦋

✨ new_fieldtype ✨

The new_fieldtype function creates a brand-new field type that's usable for data validation — it's literally birthing a new validation vibe 👑

Its parameters are function pointers, so let's break them down:

• 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 juicy details below 💖
• char_check — this function validates input characters as they are entered, one by one. 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 — basically it's the cleanup crew, no cap ��

✨ set_fieldtype_arg ✨

The set_fieldtype_arg function associates three storage-management functions with a field type — think of it as setting up your field type's entourage:

• 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. You MUST supply this one, bestie, it's not optional 💅
• copy_arg — this function may be used by applications to copy argument-blocks 📋
• free_arg — frees an argument-block structure 🗑️

okay so important detail: 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. slot it in 🔥

✨ 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 — it's giving navigation vibes 🧭

✨ link_fieldtype ✨

The link_fieldtype function creates a new field type from the two given types. They are connected by a logical "or" — so it's like, either this one OR that one, you know? 🔗

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👑 RETURN VALUE 👑

The pointer-valued routines return NULL on error. They set errno according to their success — here's the tea:

• 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)) 💀

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🌈 PORTABILITY 🌈

These routines emulate the System V forms library. They were not supported on Version 7 or BSD versions — so like, if you're on ancient stuff, sorry bestie, this ain't for you 🙈

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🍓 AUTHORS 🍓

Juergen Pfeifer. Manual pages and adaptation for new curses by Eric S. Raymond. Legends, honestly 🫶

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⭐ SEE ALSO ⭐

curses(3X), form(3X), form_field_validation(3X) — go read these next, iykyk 💜

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and that's the whole page, bestie!! you're now officially a form_fieldtype expert, periodt 💅✨

this iconic piece of documentation is from ncurses 6.5, dated 2025-01-18 — slay 🎀