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Tk_ConfigureWidget(3)	     Tk Library Procedures	 Tk_ConfigureWidget(3)

______________________________________________________________________________

NAME
       Tk_ConfigureWidget, Tk_ConfigureInfo, Tk_ConfigureValue, Tk_FreeOptions
       - process configuration options for widgets

SYNOPSIS
       #include <tk.h>

       int
       Tk_ConfigureWidget(interp, tkwin, specs, argc, argv, widgRec, flags)

       int
       Tk_ConfigureInfo(interp, tkwin, specs, widgRec, argvName, flags)

       int
       Tk_ConfigureValue(interp, tkwin, specs, widgRec, argvName, flags)

       Tk_FreeOptions(specs, widgRec, display, flags)

ARGUMENTS
       Tcl_Interp *interp (in)		    Interpreter to use	for  returning
					    error messages.

       Tk_Window tkwin (in)		    Window  used  to  represent widget
					    (needed to set up X resources).

       Tk_ConfigSpec *specs (in)	    Pointer to table specifying	 legal
					    configuration   options  for  this
					    widget.

       int argc (in)			    Number of arguments in argv.

       const char **argv (in)		    Command-line options for configur‐
					    ing widget.

       char *widgRec (in/out)		    Points to widget record structure.
					    Fields in this structure get modi‐
					    fied by Tk_ConfigureWidget to hold
					    configuration information.

       int flags (in)			    If non-zero, then it specifies  an
					    OR-ed  combination	of  flags that
					    control the processing of configu‐
					    ration    information.     TK_CON‐
					    FIG_ARGV_ONLY  causes  the	option
					    database   and   defaults	to  be
					    ignored,  and  flag	 bits  TK_CON‐
					    FIG_USER_BIT  and  higher are used
					    to selectively disable entries  in
					    specs.

       type name type (in)		    The	 name  of the type of a widget
					    record.

       field name field (in)		    The name of a field in records  of
					    type type.

       const char *argvName (in)	    The name used on Tcl command lines
					    to refer to	 a  particular	option
					    (e.g.  when	 creating  a widget or
					    invoking the configure widget com‐
					    mand).  If non-NULL, then informa‐
					    tion is  returned  only  for  this
					    option.  If NULL, then information
					    is	returned  for  all   available
					    options.

       Display *display (in)		    Display  containing	 widget	 whose
					    record is being freed;  needed  in
					    order to free up resources.
_________________________________________________________________

DESCRIPTION
       Note:  Tk_ConfigureWidget should be replaced with the new Tcl_Obj based
       API Tk_SetOptions.  The old interface is retained for backward compati‐
       bility.

       Tk_ConfigureWidget  is called to configure various aspects of a widget,
       such as colors, fonts, border width, etc.  It is intended as  a	conve‐
       nience  procedure  to reduce the amount of code that must be written in
       individual widget managers to handle configuration information.	It  is
       typically  invoked when widgets are created, and again when the config‐
       ure command is invoked for a widget.  Although intended	primarily  for
       widgets, Tk_ConfigureWidget can be used in other situations where argc-
       argv information is to be used to fill in a record structure,  such  as
       configuring  graphical  elements	 for  a	 canvas widget or entries of a
       menu.

       Tk_ConfigureWidget  processes  a	 table	specifying  the	 configuration
       options	that  are  supported  (specs) and a collection of command-line
       arguments (argc and argv) to fill in fields of a record (widgRec).   It
       uses  the  option  database  and defaults specified in specs to fill in
       fields of widgRec that are not specified in  argv.   Tk_ConfigureWidget
       normally	 returns  the  value  TCL_OK;  in this case it does not modify
       interp.	If an error occurs then TCL_ERROR is returned  and  Tk_Config‐
       ureWidget will leave an error message in interp->result in the standard
       Tcl fashion.  In the event of an error return, some of  the  fields  of
       widgRec	could  already have been set, if configuration information for
       them was successfully processed before the error occurred.   The	 other
       fields  will be set to reasonable initial values so that Tk_FreeOptions
       can be called for cleanup.

       The specs array specifies the kinds of configuration  options  expected
       by  the widget.	Each of its entries specifies one configuration option
       and has the following structure:
	      typedef struct {
		  int type;
		  char *argvName;
		  char *dbName;
		  char *dbClass;
		  char *defValue;
		  int offset;
		  int specFlags;
		  Tk_CustomOption *customPtr;
	      } Tk_ConfigSpec;
       The type field indicates what type  of  configuration  option  this  is
       (e.g.  TK_CONFIG_COLOR for a color value, or TK_CONFIG_INT for an inte‐
       ger value).  The type field indicates how  to  use  the	value  of  the
       option  (more  on  this below).	The argvName field is a string such as
       “-font” or “-bg”, which is compared with the values in argv  (if	 argv‐
       Name  is	 NULL  it  means this is a grouped entry;  see GROUPED ENTRIES
       below).	The dbName and dbClass fields are used to look up a value  for
       this  option  in	 the  option database.	The defValue field specifies a
       default value for this configuration option if no value is specified in
       either  argv or the option database.  Offset indicates where in widgRec
       to store information about this option, and  specFlags  contains	 addi‐
       tional  information  to	control	 the  processing of this configuration
       option (see FLAGS below).  The last field, customPtr, is only  used  if
       type is TK_CONFIG_CUSTOM;  see CUSTOM OPTION TYPES below.

       Tk_ConfigureWidget  first processes argv to see which (if any) configu‐
       ration options are specified there.  Argv must contain an  even	number
       of fields;  the first of each pair of fields must match the argvName of
       some entry in specs (unique abbreviations are acceptable), and the sec‐
       ond field of the pair contains the value for that configuration option.
       If there are entries in spec for which there were no  matching  entries
       in  argv,  Tk_ConfigureWidget uses the dbName and dbClass fields of the
       specs entry to probe the option database;  if a value is found, then it
       is  used as the value for the option.  Finally, if no entry is found in
       the option database, the defValue field of the specs entry is  used  as
       the value for the configuration option.	If the defValue is NULL, or if
       the TK_CONFIG_DONT_SET_DEFAULT bit is set in flags, then	 there	is  no
       default value and this specs entry will be ignored if no value is spec‐
       ified in argv or the option database.

       Once a string value has been determined	for  a	configuration  option,
       Tk_ConfigureWidget translates the string value into a more useful form,
       such as a color if type is TK_CONFIG_COLOR or an	 integer  if  type  is
       TK_CONFIG_INT.	This  value is then stored in the record pointed to by
       widgRec.	 This record is assumed to contain information relevant to the
       manager	of  the widget;	 its exact type is unknown to Tk_ConfigureWid‐
       get.  The offset field of each specs entry indicates where  in  widgRec
       to  store  the information about this configuration option.  You should
       use the Tk_Offset macro to generate offset  values  (see	 below	for  a
       description  of Tk_Offset).  The location indicated by widgRec and off‐
       set will be referred to as the “target” in the descriptions below.

       The type field of each entry in specs determines what to	 do  with  the
       string  value of that configuration option.  The legal values for type,
       and the corresponding actions, are:

       TK_CONFIG_ACTIVE_CURSOR
	      The value must be an ASCII string identifying a cursor in a form
	      suitable for passing to Tk_GetCursor.  The value is converted to
	      a Tk_Cursor by calling Tk_GetCursor and the result is stored  in
	      the  target.   In	 addition,  the	 resulting  cursor is made the
	      active cursor for tkwin by calling  XDefineCursor.   If  TK_CON‐
	      FIG_NULL_OK  is  specified in specFlags then the value may be an
	      empty string, in which case the target and tkwin's active cursor
	      will  be	set  to None.  If the previous value of the target was
	      not None, then it is freed by passing it to Tk_FreeCursor.

       TK_CONFIG_ANCHOR
	      The value must be an ASCII string identifying an anchor point in
	      one  of  the  ways accepted by Tk_GetAnchor.  The string is con‐
	      verted to a Tk_Anchor by calling Tk_GetAnchor and the result  is
	      stored in the target.

       TK_CONFIG_BITMAP
	      The value must be an ASCII string identifying a bitmap in a form
	      suitable for passing to Tk_GetBitmap.  The value is converted to
	      a Pixmap by calling Tk_GetBitmap and the result is stored in the
	      target.  If TK_CONFIG_NULL_OK is specified in specFlags then the
	      value may be an empty string, in which case the target is set to
	      None.  If the previous value of the target was not None, then it
	      is freed by passing it to Tk_FreeBitmap.

       TK_CONFIG_BOOLEAN
	      The  value  must	be an ASCII string specifying a boolean value.
	      Any of the values “true”, “yes”, “on”, or “1”, or	 an  abbrevia‐
	      tion  of	one  of	 these	values,	 means true; any of the values
	      “false”, “no”, “off”, or “0”, or an abbreviation of one of these
	      values,  means  false.  The target is expected to be an integer;
	      for true values it will be set to 1 and for false values it will
	      be set to 0.

       TK_CONFIG_BORDER
	      The  value must be an ASCII string identifying a border color in
	      a form suitable for passing to  Tk_Get3DBorder.	The  value  is
	      converted to a (Tk_3DBorder *) by calling Tk_Get3DBorder and the
	      result is stored in the target.  If TK_CONFIG_NULL_OK is	speci‐
	      fied  in	specFlags  then	 the  value may be an empty string, in
	      which case the target will be set	 to  NULL.   If	 the  previous
	      value of the target was not NULL, then it is freed by passing it
	      to Tk_Free3DBorder.

       TK_CONFIG_CAP_STYLE
	      The value must be an ASCII string identifying a cap style in one
	      of the ways accepted by Tk_GetCapStyle.  The string is converted
	      to an integer value corresponding to the cap  style  by  calling
	      Tk_GetCapStyle and the result is stored in the target.

       TK_CONFIG_COLOR
	      The  value must be an ASCII string identifying a color in a form
	      suitable for passing to Tk_GetColor.  The value is converted  to
	      an (XColor *) by calling Tk_GetColor and the result is stored in
	      the target.  If TK_CONFIG_NULL_OK is specified in specFlags then
	      the  value may be an empty string, in which case the target will
	      be set to None.  If the previous value of	 the  target  was  not
	      NULL, then it is freed by passing it to Tk_FreeColor.

       TK_CONFIG_CURSOR
	      This  option is identical to TK_CONFIG_ACTIVE_CURSOR except that
	      the new cursor is not made the active one for tkwin.

       TK_CONFIG_CUSTOM
	      This option allows applications to define new option types.  The
	      customPtr	 field of the entry points to a structure defining the
	      new option type.	See the section CUSTOM OPTION TYPES below  for
	      details.

       TK_CONFIG_DOUBLE
	      The  value  must be an ASCII floating-point number in the format
	      accepted by strtol.  The string is converted to a double	value,
	      and the value is stored in the target.

       TK_CONFIG_END
	      Marks  the  end of the table.  The last entry in specs must have
	      this type;  all of its other fields  are	ignored	 and  it  will
	      never match any arguments.

       TK_CONFIG_FONT
	      The  value  must be an ASCII string identifying a font in a form
	      suitable for passing to Tk_GetFont.  The value is converted to a
	      Tk_Font  by  calling  Tk_GetFont and the result is stored in the
	      target.  If TK_CONFIG_NULL_OK is specified in specFlags then the
	      value  may  be an empty string, in which case the target will be
	      set to NULL.  If the previous value of the target was not	 NULL,
	      then it is freed by passing it to Tk_FreeFont.

       TK_CONFIG_INT
	      The value must be an ASCII integer string in the format accepted
	      by strtol (e.g.  “0” and “0x” prefixes may be  used  to  specify
	      octal or hexadecimal numbers, respectively).  The string is con‐
	      verted to an integer value and the integer is stored in the tar‐
	      get.

       TK_CONFIG_JOIN_STYLE
	      The  value  must	be an ASCII string identifying a join style in
	      one of the ways accepted by Tk_GetJoinStyle.  The string is con‐
	      verted  to  an  integer value corresponding to the join style by
	      calling Tk_GetJoinStyle and the result is stored in the target.

       TK_CONFIG_JUSTIFY
	      The value must be an ASCII string	 identifying  a	 justification
	      method in one of the ways accepted by Tk_GetJustify.  The string
	      is converted to a Tk_Justify by calling  Tk_GetJustify  and  the
	      result is stored in the target.

       TK_CONFIG_MM
	      The  value  must	specify	 a screen distance in one of the forms
	      acceptable to Tk_GetScreenMM.  The string is converted  to  dou‐
	      ble-precision  floating-point  distance  in  millimeters and the
	      value is stored in the target.

       TK_CONFIG_PIXELS
	      The value must specify screen units in one of the forms  accept‐
	      able  to	Tk_GetPixels.	The  string is converted to an integer
	      distance in pixels and the value is stored in the target.

       TK_CONFIG_RELIEF
	      The value must be an ASCII string identifying a relief in a form
	      suitable for passing to Tk_GetRelief.  The value is converted to
	      an integer relief value by calling Tk_GetRelief and  the	result
	      is stored in the target.

       TK_CONFIG_STRING
	      A	 copy  of  the	value  is made by allocating memory space with
	      Tcl_Alloc and copying the value into  the	 dynamically-allocated
	      space.  A pointer to the new string is stored in the target.  If
	      TK_CONFIG_NULL_OK is specified in specFlags then the  value  may
	      be  an  empty  string,  in  which case the target will be set to
	      NULL.  If the previous value of the target was not NULL, then it
	      is freed by passing it to Tcl_Free.

       TK_CONFIG_SYNONYM
	      This  type  value	 identifies  special entries in specs that are
	      synonyms for other entries.  If an argv value matches the	 argv‐
	      Name  of	a  TK_CONFIG_SYNONYM  entry,  the  entry  is  not used
	      directly. Instead, Tk_ConfigureWidget searches specs for another
	      entry  whose  argvName  is  the  same as the dbName field in the
	      TK_CONFIG_SYNONYM entry;	this new entry is used just as if  its
	      argvName	had  matched  the  argv	 value.	 The synonym mechanism
	      allows multiple argv values to be used for a  single  configura‐
	      tion option, such as “-background” and “-bg”.

       TK_CONFIG_UID
	      The   value  is  translated  to  a  Tk_Uid  (by  passing	it  to
	      Tk_GetUid).  The resulting value is stored in  the  target.   If
	      TK_CONFIG_NULL_OK	 is specified in specFlags and the value is an
	      empty string then the target will be set to NULL.

       TK_CONFIG_WINDOW
	      The value must be a window path name.  It	 is  translated	 to  a
	      Tk_Window token and the token is stored in the target.

GROUPED ENTRIES
       In some cases it is useful to generate multiple resources from a single
       configuration value.  For example, a color name might be used  both  to
       generate	 the background color for a widget (using TK_CONFIG_COLOR) and
       to generate a 3-D border to  draw  around  the  widget  (using  TK_CON‐
       FIG_BORDER).  In cases like this it is possible to specify that several
       consecutive entries in specs are to be treated as a group.   The	 first
       entry  is  used	to  determine  a  value	 (using	 its argvName, dbName,
       dbClass, and defValue fields).  The value  will	be  processed  several
       times  (one for each entry in the group), generating multiple different
       resources and modifying multiple targets within widgRec.	 Each  of  the
       entries	after  the first must have a NULL value in its argvName field;
       this indicates that the entry is to be grouped with the entry that pre‐
       cedes  it.  Only the type and offset fields are used from these follow-
       on entries.

FLAGS
       The flags argument passed to Tk_ConfigureWidget is used in  conjunction
       with the specFlags fields in the entries of specs to provide additional
       control over the processing of configuration options.  These values are
       used in three different ways as described below.

       First,  if  the	flags  argument	 to Tk_ConfigureWidget has the TK_CON‐
       FIG_ARGV_ONLY bit set (i.e., flags | TK_CONFIG_ARGV_ONLY	 !=  0),  then
       the option database and defValue fields are not used.  In this case, if
       an entry in specs does not match a field in argv then nothing  happens:
       the  corresponding target is not modified.  This feature is useful when
       the goal is to modify certain configuration options while leaving  oth‐
       ers  in their current state, such as when a configure widget command is
       being processed.

       Second, the specFlags field of an entry in specs may be used to control
       the  processing of that entry.  Each specFlags field may consists of an
       OR-ed combination of the following values:

       TK_CONFIG_COLOR_ONLY
	      If this bit is set then the entry will only be considered if the
	      display  for  tkwin has more than one bit plane.	If the display
	      is monochromatic then this specs entry will be ignored.

       TK_CONFIG_MONO_ONLY
	      If this bit is set then the entry will only be considered if the
	      display  for tkwin has exactly one bit plane.  If the display is
	      not monochromatic then this specs entry will be ignored.

       TK_CONFIG_NULL_OK
	      This bit is only relevant for some types	of  entries  (see  the
	      descriptions  of the various entry types above).	If this bit is
	      set, it indicates that an empty string value for	the  field  is
	      acceptable  and  if  it  occurs then the target should be set to
	      NULL or None, depending on the type of the target.  This flag is
	      typically	 used  to  allow  a feature to be turned off entirely,
	      e.g. set a cursor value to None so that a window simply inherits
	      its  parent's cursor.  If this bit is not set then empty strings
	      are processed as strings, which generally results in an error.

       TK_CONFIG_DONT_SET_DEFAULT
	      If this bit is one, it means that	 the  defValue	field  of  the
	      entry  should  only  be  used for returning the default value in
	      Tk_ConfigureInfo.	 In calls  to  Tk_ConfigureWidget  no  default
	      will  be supplied for entries with this flag set;	 it is assumed
	      that the caller has already supplied a default value in the tar‐
	      get  location.   This  flag  provides a performance optimization
	      where it is expensive to process the default string:  the client
	      can  compute  the	 default  once, save the value, and provide it
	      before calling Tk_ConfigureWidget.

       TK_CONFIG_OPTION_SPECIFIED
	      This bit is deprecated. It used to be set and cleared by Tk_Con‐ │
	      figureWidget  so	that  callers  could  detect what entries were │
	      specified in argv, but it was removed because it was  inherently │
	      thread-unsafe.  Code  that  wishes  to  detect what options were │
	      specified should use Tk_SetOptions instead.

       The TK_CONFIG_MONO_ONLY and TK_CONFIG_COLOR_ONLY	 flags	are  typically
       used  to specify different default values for monochrome and color dis‐
       plays.  This is done by creating two entries in specs that are  identi‐
       cal  except  for their defValue and specFlags fields.  One entry should
       have the value TK_CONFIG_MONO_ONLY in its  specFlags  and  the  default
       value  for monochrome displays in its defValue;	the other entry should
       have the value TK_CONFIG_COLOR_ONLY in its specFlags and the  appropri‐
       ate defValue for color displays.

       Third,  it  is  possible	 to use flags and specFlags together to selec‐
       tively disable some entries.  This feature is not  needed  very	often.
       It is useful in cases where several similar kinds of widgets are imple‐
       mented in one place.  It allows a single specs table to be created with
       all  the configuration options for all the widget types.	 When process‐
       ing a particular widget type, only entries relevant to that  type  will
       be used.	 This effect is achieved by setting the high-order bits (those
       in positions equal to or greater than TK_CONFIG_USER_BIT) in  specFlags
       values  or  in  flags.	In order for a particular entry in specs to be
       used, its high-order bits must match exactly the high-order bits of the
       flags  value  passed  to Tk_ConfigureWidget.  If a specs table is being
       used for N different widget types, then N of the high-order  bits  will
       be  used.   Each specs entry will have one of more of those bits set in
       its specFlags field to indicate the widget types for which  this	 entry
       is  valid.   When  calling Tk_ConfigureWidget, flags will have a single
       one of these bits set to select the  entries  for  the  desired	widget
       type.   For  a  working example of this feature, see the code in tkBut‐
       ton.c.

TK_OFFSET
       The Tk_Offset macro is provided as a safe way of generating the	offset
       values  for  entries  in	 Tk_ConfigSpec structures.  It takes two argu‐
       ments:  the name of a type of record, and the name of a field  in  that
       record.	 It  returns  the byte offset of the named field in records of
       the given type.

TK_CONFIGUREINFO
       The Tk_ConfigureInfo procedure may be used to obtain information	 about
       one or all of the options for a given widget.  Given a token for a win‐
       dow (tkwin), a table describing the configuration options for  a	 class
       of widgets (specs), a pointer to a widget record containing the current
       information for a widget	 (widgRec),  and  a  NULL  argvName  argument,
       Tk_ConfigureInfo generates a string describing all of the configuration
       options for the window.	The string is placed in interp->result.	 Under
       normal  circumstances  it  returns  TCL_OK;  if an error occurs then it
       returns TCL_ERROR and interp->result contains an error message.

       If argvName is NULL, then the value left in interp->result  by  Tk_Con‐
       figureInfo  consists  of	 a  list of one or more entries, each of which
       describes one configuration option (i.e. one  entry  in	specs).	  Each
       entry  in the list will contain either two or five values.  If the cor‐
       responding entry in specs has type  TK_CONFIG_SYNONYM,  then  the  list
       will  contain  two  values:   the argvName for the entry and the dbName
       (synonym name).	Otherwise the list will contain	 five  values:	 argv‐
       Name,  dbName, dbClass, defValue, and current value.  The current value
       is computed from the appropriate field of widgRec by calling procedures
       like Tk_NameOfColor.

       If the argvName argument to Tk_ConfigureInfo is non-NULL, then it indi‐
       cates a single option,  and  information	 is  returned  only  for  that
       option.	 The string placed in interp->result will be a list containing
       two or five values as described above;  this will be identical  to  the
       corresponding  sublist  that  would  have been returned if argvName had
       been NULL.

       The flags argument to Tk_ConfigureInfo is used to  restrict  the	 specs
       entries to consider, just as for Tk_ConfigureWidget.

TK_CONFIGUREVALUE
       Tk_ConfigureValue  takes arguments similar to Tk_ConfigureInfo; instead
       of returning a list of values, it just returns the current value of the
       option  given  by  argvName  (argvName must not be NULL).  The value is
       returned in interp->result and TCL_OK is normally returned as the  pro‐
       cedure's	 result.  If an error occurs in Tk_ConfigureValue (e.g., argv‐
       Name is not a valid option name), TCL_ERROR is returned	and  an	 error
       message	is left in interp->result.  This procedure is typically called
       to implement cget widget commands.

TK_FREEOPTIONS
       The Tk_FreeOptions procedure may be invoked during  widget  cleanup  to
       release all of the resources associated with configuration options.  It
       scans through specs and for each entry corresponding to a resource that
       must  be	 explicitly  freed  (e.g. those with type TK_CONFIG_COLOR), it
       frees the resource in the widget record.	 If the field  in  the	widget
       record  does not refer to a resource (e.g.  it contains a null pointer)
       then no resource is freed for that entry.  After	 freeing  a  resource,
       Tk_FreeOptions  sets  the  corresponding	 field of the widget record to
       null.

CUSTOM OPTION TYPES
       Applications can extend the built-in  configuration  types  with	 addi‐
       tional  configuration  types  by	 writing procedures to parse and print
       options of the a type and creating a structure pointing to those proce‐
       dures:
	      typedef struct Tk_CustomOption {
		  Tk_OptionParseProc *parseProc;
		  Tk_OptionPrintProc *printProc;
		  ClientData clientData;
	      } Tk_CustomOption;

	      typedef int Tk_OptionParseProc(
		  ClientData clientData,
		  Tcl_Interp *interp,
		  Tk_Window tkwin,
		  char *value,
		  char *widgRec,
		  int offset);

	      typedef char *Tk_OptionPrintProc(
		  ClientData clientData,
		  Tk_Window tkwin,
		  char *widgRec,
		  int offset,
		  Tcl_FreeProc **freeProcPtr);
       The Tk_CustomOption structure contains three fields, which are pointers
       to the two procedures and a clientData value to be passed to those pro‐
       cedures	when  they are invoked.	 The clientData value typically points
       to a structure containing information that is needed by the  procedures
       when they are parsing and printing options.

       The  parseProc  procedure  is  invoked by Tk_ConfigureWidget to parse a
       string and store the resulting value in the widget record.  The client‐
       Data  argument is a copy of the clientData field in the Tk_CustomOption
       structure.  The interp argument points to a Tcl	interpreter  used  for
       error  reporting.   Tkwin is a copy of the tkwin argument to Tk_Config‐
       ureWidget.  The value argument is a string describing the value for the
       option;	it could have been specified explicitly in the call to Tk_Con‐
       figureWidget or it could come from the option database  or  a  default.
       Value will never be a null pointer but it may point to an empty string.
       RecordPtr is the same as the widgRec  argument  to  Tk_ConfigureWidget;
       it  points to the start of the widget record to modify.	The last argu‐
       ment, offset, gives the offset in bytes from the start  of  the	widget
       record  to  the	location  where the option value is to be placed.  The
       procedure should translate the string to whatever form  is  appropriate
       for  the	 option	 and  store the value in the widget record.  It should
       normally return TCL_OK, but if  an  error  occurs  in  translating  the
       string  to  a  value then it should return TCL_ERROR and store an error
       message in interp->result.

       The printProc procedure is called  by  Tk_ConfigureInfo	to  produce  a
       string  value  describing  an  existing option.	Its clientData, tkwin,
       widgRec, and  offset  arguments	all  have  the	same  meaning  as  for
       Tk_OptionParseProc  procedures.	The printProc procedure should examine
       the option whose value is stored at offset in widgRec, produce a string
       describing  that	 option,  and  return a pointer to the string.	If the
       string is stored in dynamically-allocated memory,  then	the  procedure
       must set *freeProcPtr to the address of a procedure to call to free the
       string's memory;	 Tk_ConfigureInfo will call this procedure when it  is
       finished	 with  the  string.   If the result string is stored in static
       memory then printProc need not do anything with the  freeProcPtr	 argu‐
       ment.

       Once  parseProc	and  printProc have been defined and a Tk_CustomOption
       structure has been created for them, options of this new	 type  may  be
       manipulated  with  Tk_ConfigSpec	 entries whose type fields are TK_CON‐
       FIG_CUSTOM and whose customPtr  fields  point  to  the  Tk_CustomOption
       structure.

EXAMPLES
       Although	 the  explanation of Tk_ConfigureWidget is fairly complicated,
       its actual use is pretty	 straightforward.   The	 easiest  way  to  get
       started	is  to	copy  the  code	 from an existing widget.  The library
       implementation of frames (tkFrame.c) has a simple configuration	table,
       and  the library implementation of buttons (tkButton.c) has a much more
       complex table that uses many of the fancy specFlags mechanisms.

SEE ALSO
       Tk_SetOptions(3)

KEYWORDS
       anchor,	bitmap,	 boolean,  border,  cap	 style,	 color,	 configuration
       options,	 cursor,  custom,  double, font, integer, join style, justify,
       millimeters, pixels, relief, synonym, uid

Tk				      4.1		 Tk_ConfigureWidget(3)
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