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driver(3FORM) Library calls driver(3FORM)


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


#include <form.h>
int form_driver(FORM *form, int c);
int form_driver_w(FORM *form, int c, wchar_t wch);



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(3NCURSES).
  • 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.


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(3NCURSES). 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 beginning of field.
REQ_BEG_LINE Move to 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 cursor.
REQ_DOWN_CHAR Move down in field.
REQ_DOWN_FIELD Move down to a field.
REQ_END_FIELD Move to the end of 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 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 field.
REQ_RIGHT_FIELD Move right to a field.
REQ_SCR_BCHAR Scroll field backward 1 character.
REQ_SCR_BHPAGE Scroll field backward ½ page.
REQ_SCR_BLINE Scroll field backward 1 line.
REQ_SCR_BPAGE Scroll field backward 1 page.
REQ_SCR_FCHAR Scroll field forward 1 character.
REQ_SCR_FHPAGE Scroll field forward ½ page.
REQ_SCR_FLINE Scroll field forward 1 line.
REQ_SCR_FPAGE Scroll field forward 1 page.
REQ_SCR_HBHALF Horizontal scroll field backward ½ line.
REQ_SCR_HBLINE Horizontal scroll field backward 1 line.
REQ_SCR_HFHALF Horizontal scroll field forward ½ line.
REQ_SCR_HFLINE Horizontal scroll field forward 1 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 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:

If you click below the display region of the form:

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.


form_driver returns one of the following error codes:

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


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.


ncurses(3NCURSES), form(3FORM), fieldtype(3FORM), field_buffer(3FORM), field_validation(3FORM), form_variables(3FORM), getch(3NCURSES)

2024-03-16 ncurses 6.4