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Tcl_StringObj(3)	    Tcl Library Procedures	      Tcl_StringObj(3)

______________________________________________________________________________

NAME
       Tcl_NewStringObj,   Tcl_NewUnicodeObj,	Tcl_SetStringObj,  Tcl_SetUni‐
       codeObj,	 Tcl_GetStringFromObj,	Tcl_GetString,	Tcl_GetUnicodeFromObj,
       Tcl_GetUnicode,	  Tcl_GetUniChar,   Tcl_GetCharLength,	 Tcl_GetRange,
       Tcl_AppendToObj,	     Tcl_AppendUnicodeToObj,	   Tcl_AppendObjToObj,
       Tcl_AppendStringsToObj,	 Tcl_AppendStringsToObjVA,  Tcl_AppendLimited‐
       ToObj, Tcl_Format,  Tcl_AppendFormatToObj,  Tcl_ObjPrintf,  Tcl_Append‐
       PrintfToObj, Tcl_SetObjLength, Tcl_AttemptSetObjLength, Tcl_ConcatObj -
       manipulate Tcl values as strings

SYNOPSIS
       #include <tcl.h>

       Tcl_Obj *
       Tcl_NewStringObj(bytes, length)

       Tcl_Obj *
       Tcl_NewUnicodeObj(unicode, numChars)

       void
       Tcl_SetStringObj(objPtr, bytes, length)

       void
       Tcl_SetUnicodeObj(objPtr, unicode, numChars)

       char *
       Tcl_GetStringFromObj(objPtr, lengthPtr)

       char *
       Tcl_GetString(objPtr)

       Tcl_UniChar *
       Tcl_GetUnicodeFromObj(objPtr, lengthPtr)

       Tcl_UniChar *
       Tcl_GetUnicode(objPtr)

       Tcl_UniChar
       Tcl_GetUniChar(objPtr, index)

       int
       Tcl_GetCharLength(objPtr)

       Tcl_Obj *
       Tcl_GetRange(objPtr, first, last)

       void
       Tcl_AppendToObj(objPtr, bytes, length)

       void
       Tcl_AppendUnicodeToObj(objPtr, unicode, numChars)

       void
       Tcl_AppendObjToObj(objPtr, appendObjPtr)

       void
       Tcl_AppendStringsToObj(objPtr, string, string, ... (char *) NULL)

       void
       Tcl_AppendStringsToObjVA(objPtr, argList)

       void
       Tcl_AppendLimitedToObj(objPtr, bytes, length, limit, ellipsis)

       Tcl_Obj *
       Tcl_Format(interp, format, objc, objv)

       int
       Tcl_AppendFormatToObj(interp, objPtr, format, objc, objv)

       Tcl_Obj *
       Tcl_ObjPrintf(format, ...)

       void
       Tcl_AppendPrintfToObj(objPtr, format, ...)

       void
       Tcl_SetObjLength(objPtr, newLength)

       int
       Tcl_AttemptSetObjLength(objPtr, newLength)

       Tcl_Obj *
       Tcl_ConcatObj(objc, objv)

ARGUMENTS
       const char *bytes (in)			     Points to the first  byte
						     of	    an	   array    of
						     UTF-8-encoded bytes  used
						     to	 set  or  append  to a
						     string value.  This  byte
						     array  may contain embed‐
						     ded    null    characters
						     unless  numChars is nega‐
						     tive.	 (Applications
						     needing null bytes should
						     represent	them  as   the
						     two-byte	      sequence
						     \700\600,		   use
						     Tcl_ExternalToUtf to con‐
						     vert,  or	Tcl_NewByteAr‐
						     rayObj if the string is a
						     collection	 of   uninter‐
						     preted bytes.)

       int length (in)				     The  number  of  bytes to
						     copy from bytes when ini‐
						     tializing,	  setting,  or
						     appending	to  a	string
						     value.   If negative, all
						     bytes  up	to  the	 first
						     null are used.

       const Tcl_UniChar *unicode (in)		     Points  to the first byte
						     of an  array  of  Unicode
						     characters used to set or
						     append to a string value.
						     This  byte array may con‐
						     tain embedded null	 char‐
						     acters unless numChars is
						     negative.

       int numChars (in)			     The  number  of   Unicode
						     characters	 to  copy from
						     unicode  when  initializ‐
						     ing,  setting, or append‐
						     ing to  a	string	value.
						     If	 negative, all charac‐
						     ters up to the first null
						     character are used.

       int index (in)				     The  index of the Unicode
						     character to return.

       int first (in)				     The index	of  the	 first
						     Unicode  character in the
						     Unicode   range   to   be
						     returned as a new value.

       int last (in)				     The  index	 of  the  last
						     Unicode character in  the
						     Unicode   range   to   be
						     returned as a new value.

       Tcl_Obj *objPtr (in/out)			     Points  to	 a  value   to
						     manipulate.

       Tcl_Obj *appendObjPtr (in)		     The  value	 to  append to
						     objPtr in	Tcl_AppendObj‐
						     ToObj.

       int *lengthPtr (out)			     If non-NULL, the location
						     where   Tcl_GetStringFro‐
						     mObj   will   store   the
						     length   of   a   value's
						     string representation.

       const char *string (in)			     Null-terminated	string
						     value   to	  append    to
						     objPtr.

       va_list argList (in)			     An	 argument  list	 which
						     must have	been  initial‐
						     ized  using va_start, and
						     cleared using va_end.

       int limit (in)				     Maximum number  of	 bytes
						     to be appended.

       const char *ellipsis (in)		     Suffix to append when the
						     limit  leads  to	string
						     truncation.   If  NULL is
						     passed  then  the	suffix
						     “...”  is used.

       const char *format (in)			     Format   control	string
						     including	%   conversion
						     specifiers.

       int objc (in)				     The number of elements to
						     format or concatenate.

       Tcl_Obj *objv[] (in)			     The array	of  values  to
						     format or concatenate.

       int newLength (in)			     New length for the string
						     value  of	 objPtr,   not
						     including	the final null
						     character.
_________________________________________________________________

DESCRIPTION
       The procedures described in this manual entry allow Tcl	values	to  be
       manipulated  as string values.  They use the internal representation of
       the value to store additional information to make the string  manipula‐
       tions  more  efficient.	 In  particular,  they make a series of append
       operations efficient by allocating extra storage space for  the	string
       so  that it does not have to be copied for each append.	Also, indexing
       and length computations are optimized because the Unicode string repre‐
       sentation   is  calculated  and	cached	as  needed.   When  using  the
       Tcl_Append* family of functions where the interpreter's result  is  the
       value  being appended to, it is important to call Tcl_ResetResult first
       to ensure you are not unintentionally appending to existing data in the
       result value.

       Tcl_NewStringObj	 and  Tcl_SetStringObj create a new value or modify an
       existing value to hold a copy of the string given by bytes and  length.
       Tcl_NewUnicodeObj and Tcl_SetUnicodeObj create a new value or modify an
       existing value to hold a copy of the Unicode string  given  by  unicode
       and  numChars.  Tcl_NewStringObj and Tcl_NewUnicodeObj return a pointer
       to a newly created value with reference count zero.   All  four	proce‐
       dures  set  the value to hold a copy of the specified string.  Tcl_Set‐
       StringObj and Tcl_SetUnicodeObj free any old string  representation  as
       well as any old internal representation of the value.

       Tcl_GetStringFromObj  and  Tcl_GetString return a value's string repre‐
       sentation.  This is  given  by  the  returned  byte  pointer  and  (for
       Tcl_GetStringFromObj)  length,  which  is  stored in lengthPtr if it is
       non-NULL.  If the value's UTF string  representation  is	 invalid  (its
       byte  pointer  is  NULL), the string representation is regenerated from
       the value's internal representation.  The  storage  referenced  by  the
       returned byte pointer is owned by the value manager.  It is passed back
       as a writable pointer so	 that  extension  author  creating  their  own
       Tcl_ObjType will be able to modify the string representation within the
       Tcl_UpdateStringProc of their Tcl_ObjType.   Except  for	 that  limited
       purpose,	 the pointer returned by Tcl_GetStringFromObj or Tcl_GetString
       should be treated as read-only.	It is recommended that this pointer be
       assigned	 to a (const char *) variable.	Even in the limited situations
       where writing to this pointer is acceptable, one should	take  care  to
       respect	the copy-on-write semantics required by Tcl_Obj's, with appro‐
       priate calls to Tcl_IsShared and Tcl_DuplicateObj prior to any in-place
       modification of the string representation.  The procedure Tcl_GetString
       is used in the common case where the caller does not need the length of
       the string representation.

       Tcl_GetUnicodeFromObj  and  Tcl_GetUnicode  return a value's value as a
       Unicode string.	This  is  given	 by  the  returned  pointer  and  (for
       Tcl_GetUnicodeFromObj)  length,	which  is stored in lengthPtr if it is
       non-NULL.  The storage referenced by the returned byte pointer is owned
       by  the	value  manager	and should not be modified by the caller.  The
       procedure Tcl_GetUnicode is used in the common case  where  the	caller
       does not need the length of the unicode string representation.

       Tcl_GetUniChar  returns	the  index'th character in the value's Unicode
       representation.

       Tcl_GetRange returns a newly created value comprised of the  characters
       between	first  and last (inclusive) in the value's Unicode representa‐
       tion.  If the value's Unicode representation is	invalid,  the  Unicode
       representation is regenerated from the value's string representation.

       Tcl_GetCharLength  returns  the	number	of  characters	(as opposed to
       bytes) in the string value.

       Tcl_AppendToObj appends the data given  by  bytes  and  length  to  the
       string  representation  of the value specified by objPtr.  If the value
       has an invalid string representation, then an attempt is made  to  con‐
       vert  bytes is to the Unicode format.  If the conversion is successful,
       then the converted form of bytes is appended  to	 the  value's  Unicode
       representation.	 Otherwise,  the  value's  Unicode  representation  is
       invalidated and converted to the UTF format, and bytes is  appended  to
       the value's new string representation.

       Tcl_AppendUnicodeToObj  appends the Unicode string given by unicode and
       numChars to the value specified by objPtr.  If the value has an invalid
       Unicode representation, then unicode is converted to the UTF format and
       appended to the value's string representation.  Appends	are  optimized
       to  handle  repeated  appends relatively efficiently (it over-allocates
       the string or Unicode space to avoid repeated reallocations and	copies
       of value's string value).

       Tcl_AppendObjToObj  is  similar	to Tcl_AppendToObj, but it appends the
       string or Unicode value (whichever exists and  is  best	suited	to  be
       appended to objPtr) of appendObjPtr to objPtr.

       Tcl_AppendStringsToObj is similar to Tcl_AppendToObj except that it can
       be passed more than one value to append and each value must be a	 null-
       terminated  string  (i.e.  none of the values may contain internal null
       characters).  Any number of string arguments may be provided,  but  the
       last argument must be a NULL pointer to indicate the end of the list.

       Tcl_AppendStringsToObjVA	 is  the same as Tcl_AppendStringsToObj except
       that instead of taking a variable number of arguments it takes an argu‐
       ment list.

       Tcl_AppendLimitedToObj  is  similar  to	Tcl_AppendToObj except that it
       imposes a limit on how many bytes are appended.	This can be handy when
       the string to be appended might be very large, but the value being con‐
       structed should not be allowed to grow without bound. A common usage is
       when constructing an error message, where the end result should be kept
       short enough to be read.	 Bytes from bytes are appended to objPtr,  but
       no  more	 than  limit bytes total are to be appended. If the limit pre‐
       vents all length bytes that are available from being appended, then the
       appending  is  done so that the last bytes appended are from the string
       ellipsis. This allows for an indication of the truncation to be left in
       the string.  When length is -1, all bytes up to the first zero byte are
       appended, subject to the limit. When  ellipsis  is  NULL,  the  default
       string ... is used. When ellipsis is non-NULL, it must point to a zero-
       byte-terminated string in Tcl's internal UTF encoding.  The  number  of
       bytes  appended	can  be	 less than the lesser of length and limit when
       appending fewer bytes is necessary  to  append  only  whole  multi-byte
       characters.

       Tcl_Format  is  the  C-level interface to the engine of the format com‐
       mand.  The actual command procedure for format is little more than

	      Tcl_Format(interp, Tcl_GetString(objv[1]), objc-2, objv+2);

       The objc Tcl_Obj values in objv are formatted into a  string  according
       to the conversion specification in format argument, following the docu‐
       mentation for the format command.  The resulting	 formatted  string  is
       converted to a new Tcl_Obj with refcount of zero and returned.  If some
       error happens during  production	 of  the  formatted  string,  NULL  is
       returned, and an error message is recorded in interp, if interp is non-
       NULL.

       Tcl_AppendFormatToObj is an appending alternative  form	of  Tcl_Format
       with functionality equivalent to:

	      Tcl_Obj *newPtr = Tcl_Format(interp, format, objc, objv);
	      if (newPtr == NULL) return TCL_ERROR;
	      Tcl_AppendObjToObj(objPtr, newPtr);
	      return TCL_OK;

       but  with  greater  convenience and efficiency when the appending func‐
       tionality is needed.

       Tcl_ObjPrintf serves as a replacement for the common sequence

	      char buf[SOME_SUITABLE_LENGTH];
	      sprintf(buf, format, ...);
	      Tcl_NewStringObj(buf, -1);

       but with greater	 convenience  and  no  need  to	 determine  SOME_SUIT‐
       ABLE_LENGTH.  The  formatting  is  done	with  the same core formatting
       engine used by Tcl_Format.  This means the set of supported  conversion
       specifiers  is  that  of the format command and not that of the sprintf
       routine where the two sets differ. When a conversion  specifier	passed
       to  Tcl_ObjPrintf  includes a precision, the value is taken as a number
       of bytes, as sprintf does, and not as a number of characters, as format
       does.   This  is	 done  on the assumption that C code is more likely to
       know how many bytes it is passing around than  the  number  of  encoded
       characters  those  bytes	 happen	 to represent.	The variable number of
       arguments passed in should be of the types that would be	 suitable  for
       passing to sprintf.  Note in this example usage, x is of type int.

	      int x = 5;
	      Tcl_Obj *objPtr = Tcl_ObjPrintf("Value is %d", x);

       If  the	value  of  format contains internal inconsistencies or invalid
       specifier  formats,   the   formatted   string	result	 produced   by
       Tcl_ObjPrintf  will  be	an  error message describing the error.	 It is
       impossible however to provide  runtime  protection  against  mismatches
       between	the format and any subsequent arguments.  Compile-time protec‐
       tion may be provided by some compilers.

       Tcl_AppendPrintfToObj is an appending alternative form of Tcl_ObjPrintf
       with functionality equivalent to

	      Tcl_AppendObjToObj(objPtr, Tcl_ObjPrintf(format, ...));

       but  with  greater  convenience and efficiency when the appending func‐
       tionality is needed.

       The Tcl_SetObjLength procedure changes the length of the	 string	 value
       of  its objPtr argument.	 If the newLength argument is greater than the
       space allocated for the value's string, then the string space is	 real‐
       located and the old value is copied to the new space; the bytes between
       the old length of the string and the new length may have arbitrary val‐
       ues.   If the newLength argument is less than the current length of the
       value's string, with objPtr->length is reduced without reallocating the
       string space; the original allocated size for the string is recorded in
       the value, so that the string length can be enlarged  in	 a  subsequent
       call  to	 Tcl_SetObjLength  without reallocating storage.  In all cases
       Tcl_SetObjLength leaves a null character at objPtr->bytes[newLength].

       Tcl_AttemptSetObjLength is identical in	function  to  Tcl_SetObjLength
       except that if sufficient memory to satisfy the request cannot be allo‐
       cated, it does not cause	 the  Tcl  interpreter	to  panic.   Thus,  if
       newLength  is  greater than the space allocated for the value's string,
       and there is not	 enough	 memory	 available  to	satisfy	 the  request,
       Tcl_AttemptSetObjLength	will  take  no action and return 0 to indicate
       failure.	  If  there  is	 enough	 memory	 to   satisfy	the   request,
       Tcl_AttemptSetObjLength	behaves just like Tcl_SetObjLength and returns
       1 to indicate success.

       The Tcl_ConcatObj function returns a new string value  whose  value  is
       the  space-separated concatenation of the string representations of all
       of the values in the objv array. Tcl_ConcatObj eliminates  leading  and
       trailing	 white	space  as  it copies the string representations of the
       objv array to the result. If an element of the objv array  consists  of
       nothing	but  white  space,  then  that value is ignored entirely. This
       white-space removal was added to make the output of the concat  command
       cleaner-looking.	 Tcl_ConcatObj	returns	 a  pointer to a newly-created
       value whose ref count is zero.

SEE ALSO
       Tcl_NewObj(3),  Tcl_IncrRefCount(3),  Tcl_DecrRefCount(3),   format(n),
       sprintf(3)

KEYWORDS
       append,	internal  representation,  value,  value  type,	 string value,
       string type, string representation, concat, concatenate, unicode

Tcl				      8.1		      Tcl_StringObj(3)
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