form_driver.3x - Man Page

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(3X).
  • 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(3X). 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:

REQ_BEG_FIELDMove to the beginning of the field.
REQ_BEG_LINEMove to the beginning of the line.
REQ_CLR_EOFClear to end of field from cursor.
REQ_CLR_EOLClear to end of line from cursor.
REQ_CLR_FIELDClear the entire field.
REQ_DEL_CHARDelete character at the cursor.
REQ_DEL_LINEDelete line at the cursor.
REQ_DEL_PREVDelete character before the cursor.
REQ_DEL_WORDDelete blank-delimited word at the cursor.
REQ_DOWN_CHARMove down in the field.
REQ_DOWN_FIELDMove down to a field.
REQ_END_FIELDMove to the end of the field.
REQ_END_LINEMove to the end of the line.
REQ_FIRST_FIELDMove to the first field.
REQ_FIRST_PAGEMove to the first page.
REQ_INS_CHARInsert a blank at the cursor.
REQ_INS_LINEInsert a blank line at the cursor.
REQ_INS_MODEEnter insert mode.
REQ_LAST_FIELDMove to the last field.
REQ_LAST_PAGEMove to the last field.
REQ_LEFT_CHARMove left in the field.
REQ_LEFT_FIELDMove left to a field.
REQ_NEW_LINEInsert or overlay a new line.
REQ_NEXT_CHARMove to the next char.
REQ_NEXT_CHOICEDisplay next field choice.
REQ_NEXT_FIELDMove to the next field.
REQ_NEXT_LINEMove to the next line.
REQ_NEXT_PAGEMove to the next page.
REQ_NEXT_PAGEMove to the next page.
REQ_NEXT_WORDMove to the next word.
REQ_OVL_MODEEnter overlay mode.
REQ_PREV_CHARMove to the previous char.
REQ_PREV_CHOICEDisplay previous field choice.
REQ_PREV_FIELDMove to the previous field.
REQ_PREV_LINEMove to the previous line.
REQ_PREV_PAGEMove to the previous page.
REQ_PREV_WORDMove to the previous word.
REQ_RIGHT_CHARMove right in the field.
REQ_RIGHT_FIELDMove right to a field.
REQ_SCR_BCHARScroll the field backward a character.
REQ_SCR_BHPAGEScroll the field backward half a page.
REQ_SCR_BLINEScroll the field backward a line.
REQ_SCR_BPAGEScroll the field backward a page.
REQ_SCR_FCHARScroll the field forward a character.
REQ_SCR_FHPAGEScroll the field forward half a page.
REQ_SCR_FLINEScroll the field forward a line.
REQ_SCR_FPAGEScroll the field forward a page.
REQ_SCR_HBHALFHorizontal scroll the field backward half a line.
REQ_SCR_HBLINEHorizontal scroll the field backward a line.
REQ_SCR_HFHALFHorizontal scroll the field forward half a line.
REQ_SCR_HFLINEHorizontal scroll the field forward a line.
REQ_SFIRST_FIELDMove to the sorted first field.
REQ_SLAST_FIELDMove to the sorted last field.
REQ_SNEXT_FIELDMove to the sorted next field.
REQ_SPREV_FIELDMove to the sorted previous field.
REQ_UP_CHARMove up in the field.
REQ_UP_FIELDMove up to a field.
REQ_VALIDATIONValidate 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:


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.

See Also

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


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


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.

Referenced By

The man page form_driver_w.3x(3) is an alias of form_driver.3x(3).