form_driver(3) | Library calls | form_driver(3)

# NAME

form_driver, form_driver_w - command-processing loop of the form system

# SYNOPSIS

#include <form.h>

int form_driver(FORM *form, int c);
int form_driver_w(FORM *form, int c, wchar_t wch);

# DESCRIPTION

## form_driver

Once a form has been posted (displayed), you should funnel input events to it through form_driver. This routine has three major input cases:

- The input is a form navigation request. Navigation request codes are constants defined in <form.h>, which are distinct from the key- and character codes returned by wgetch(3).
- The input is a printable character. Printable characters (which must be positive, less than 256) are checked according to the program's locale settings.
- The input is the KEY_MOUSE special key associated with an mouse event.

## form_driver_w

This extension simplifies the use of the forms library using wide characters. The input is either a key code (a request) or a wide character returned by get_wch(3). The type must be passed as well, to enable the library to determine whether the parameter is a wide character or a request.

## Form-driver requests

The form driver requests are as follows:

Name | Description
REQ_BEG_FIELD | Move to the beginning of the field.
REQ_BEG_LINE | Move to the beginning of the line.
REQ_CLR_EOF | Clear to end of field from cursor.
REQ_CLR_EOL | Clear to end of line from cursor.
REQ_CLR_FIELD | Clear the entire field.
REQ_DEL_CHAR | Delete character at the cursor.
REQ_DEL_LINE | Delete line at the cursor.
REQ_DEL_PREV | Delete character before the cursor.
REQ_DEL_WORD | Delete blank-delimited word at the cursor.
REQ_DOWN_CHAR | Move down in the field.
REQ_DOWN_FIELD | Move down to a field.
REQ_END_FIELD | Move to the end of the field.
REQ_END_LINE | Move to the end of the line.
REQ_FIRST_FIELD | Move to the first field.
REQ_FIRST_PAGE | Move to the first page.
REQ_INS_CHAR | Insert a blank at the cursor.
REQ_INS_LINE | Insert a blank line at the cursor.
REQ_INS_MODE | Enter insert mode.
REQ_LAST_FIELD | Move to the last field.
REQ_LAST_PAGE | Move to the last field.
REQ_LEFT_CHAR | Move left in the field.
REQ_LEFT_FIELD | Move left to a field.
REQ_NEW_LINE | Insert or overlay a new line.
REQ_NEXT_CHAR | Move to the next char.
REQ_NEXT_CHOICE | Display next field choice.
REQ_NEXT_FIELD | Move to the next field.
REQ_NEXT_LINE | Move to the next line.
REQ_NEXT_PAGE | Move to the next page.
REQ_NEXT_PAGE | Move to the next page.
REQ_NEXT_WORD | Move to the next word.
REQ_OVL_MODE | Enter overlay mode.
REQ_PREV_CHAR | Move to the previous char.
REQ_PREV_CHOICE | Display previous field choice.
REQ_PREV_FIELD | Move to the previous field.
REQ_PREV_LINE | Move to the previous line.
REQ_PREV_PAGE | Move to the previous page.
REQ_PREV_WORD | Move to the previous word.
REQ_RIGHT_CHAR | Move right in the field.
REQ_RIGHT_FIELD | Move right to a field.
REQ_SCR_BCHAR | Scroll the field backward a character.
REQ_SCR_BHPAGE | Scroll the field backward half a page.
REQ_SCR_BLINE | Scroll the field backward a line.
REQ_SCR_BPAGE | Scroll the field backward a page.
REQ_SCR_FCHAR | Scroll the field forward a character.
REQ_SCR_FHPAGE | Scroll the field forward half a page.
REQ_SCR_FLINE | Scroll the field forward a line.
REQ_SCR_FPAGE | Scroll the field forward a page.
REQ_SCR_HBHALF | Horizontal scroll the field backward half a line.
REQ_SCR_HBLINE | Horizontal scroll the field backward a line.
REQ_SCR_HFHALF | Horizontal scroll the field forward half a line.
REQ_SCR_HFLINE | Horizontal scroll the field forward a line.
REQ_SFIRST_FIELD | Move to the sorted first field.
REQ_SLAST_FIELD | Move to the sorted last field.
REQ_SNEXT_FIELD | Move to the sorted next field.
REQ_SPREV_FIELD | Move to the sorted previous field.
REQ_UP_CHAR | Move up in the field.
REQ_UP_FIELD | Move up to a field.
REQ_VALIDATION | Validate field.

If the second argument is a printable character, the driver places it in the current position in the current field. If it is one of the forms requests listed above, that request is executed.

## Field validation

The form library makes updates to the window associated with form fields rather than directly to the field buffers.

The form driver provides low-level control over updates to the form fields. The form driver also provides for validating modified fields to ensure that the contents meet whatever constraints an application may attach using set_field_type.

You can validate a field without making any changes to it using REQ_VALIDATION. The form driver also validates a field in these cases:

- a call to set_current_field attempts to move to a different field.
- a call to set_current_page attempts to move to a different page of the form.
- a request attempts to move to a different field.
- a request attempts to move to a different page of the form.

In each case, the move fails if the field is invalid.

If the modified field is valid, the form driver copies the modified data from the window associated with the field to the field buffer.

## Mouse handling

If the second argument is the KEY_MOUSE special key, the associated mouse event is translated into one of the above pre-defined requests. Currently only clicks in the user window (e.g., inside the form display area or the decoration window) are handled.

If you click above the display region of the form:

a REQ_PREV_FIELD is generated for a single click,
a REQ_PREV_PAGE is generated for a double-click and
a REQ_FIRST_FIELD is generated for a triple-click.

If you click below the display region of the form:

a REQ_NEXT_FIELD is generated for a single click,
a REQ_NEXT_PAGE is generated for a double-click and
a REQ_LAST_FIELD is generated for a triple-click.

If you click at an field inside the display area of the form:

- the form cursor is positioned to that field.
- If you double-click a field, the form cursor is positioned to that field and E_UNKNOWN_COMMAND is returned. This return value makes sense, because a double click usually means that an field-specific action should be returned. It is exactly the purpose of this return value to signal that an application specific command should be executed.
- If a translation into a request was done, form_driver returns the result of this request.

If you clicked outside the user window or the mouse event could not be translated into a form request an E_REQUEST_DENIED is returned.

## Application-defined commands

If the second argument is neither printable nor one of the above pre-defined form requests, the driver assumes it is an application-specific command and returns E_UNKNOWN_COMMAND. Application-defined commands should be defined relative to MAX_COMMAND, the maximum value of these pre-defined requests.

# RETURN VALUE

form_driver returns one of the following error codes:

E_OK
  The routine succeeded.
E_BAD_ARGUMENT
  Routine detected an incorrect or out-of-range argument.
E_BAD_STATE
  Routine was called from an initialization or termination function.
E_NOT_POSTED
  The form has not been posted.
E_INVALID_FIELD
  Contents of field is invalid.
E_NOT_CONNECTED
  No fields are connected to the form.
E_REQUEST_DENIED
  The form driver could not process the request.
E_SYSTEM_ERROR
  System error occurred (see errno(3)).
E_UNKNOWN_COMMAND
  The form driver code saw an unknown request code.

# SEE ALSO

curses(3), form(3), form_fieldtype(3), form_field_buffer(3), form_field_validation(3), form_variables(3), getch(3).

# NOTES

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

# PORTABILITY

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

# AUTHORS

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

2023-08-19 | ncurses 6.4