Provided by: tcl8.5-doc_8.5.19-4_all 
NAME
Tcl_NewStringObj, Tcl_NewUnicodeObj, Tcl_SetStringObj, Tcl_SetUnicodeObj, 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_AppendLimitedToObj, Tcl_Format, Tcl_AppendFormatToObj, Tcl_ObjPrintf,
Tcl_AppendPrintfToObj, Tcl_SetObjLength, Tcl_AttemptSetObjLength, Tcl_ConcatObj - manipulate Tcl objects
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, ...) │
int │
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 object. This byte array
may contain embedded null characters unless numChars is
negative. (Applications needing null bytes should
represent them as the two-byte sequence \700\600, use
Tcl_ExternalToUtf to convert, or Tcl_NewByteArrayObj if the
string is a collection of uninterpreted bytes.)
int length (in) The number of bytes to copy from bytes when initializing,
setting, or appending to a string object. 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 object. This byte array
may contain embedded null characters unless numChars is
negative.
int numChars (in) The number of Unicode characters to copy from unicode when
initializing, setting, or appending to a string object. If
negative, all characters 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 object.
int last (in) The index of the last Unicode character in the Unicode
range to be returned as a new object.
Tcl_Obj *objPtr (in/out) Points to an object to manipulate.
Tcl_Obj *appendObjPtr (in) The object to append to objPtr in Tcl_AppendObjToObj.
int *lengthPtr (out) If non-NULL, the location where Tcl_GetStringFromObj will
store the length of an object'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 initialised 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 objects 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 objects to be manipulated as string values. They
use the internal representation of the object to store additional information to make the string
manipulations 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 representation is
calculated and cached as needed. When using the Tcl_Append* family of functions where the interpreter's
result is the object being appended to, it is important to call Tcl_ResetResult first to ensure you are
not unintentionally appending to existing data in the result object.
Tcl_NewStringObj and Tcl_SetStringObj create a new object or modify an existing object to hold a copy of
the string given by bytes and length. Tcl_NewUnicodeObj and Tcl_SetUnicodeObj create a new object or
modify an existing object 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 object with reference count
zero. All four procedures set the object to hold a copy of the specified string. Tcl_SetStringObj and
Tcl_SetUnicodeObj free any old string representation as well as any old internal representation of the
object.
Tcl_GetStringFromObj and Tcl_GetString return an object's string representation. 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 object's UTF string representation is invalid (its byte pointer is NULL), the string
representation is regenerated from the object's internal representation. The storage referenced by the
returned byte pointer is owned by the object 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 appropriate 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 an object'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 object 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 object's Unicode representation.
Tcl_GetRange returns a newly created object comprised of the characters between first and last
(inclusive) in the object's Unicode representation. If the object's Unicode representation is invalid,
the Unicode representation is regenerated from the object's string representation.
Tcl_GetCharLength returns the number of characters (as opposed to bytes) in the string object.
Tcl_AppendToObj appends the data given by bytes and length to the string representation of the object
specified by objPtr. If the object has an invalid string representation, then an attempt is made to
convert bytes is to the Unicode format. If the conversion is successful, then the converted form of
bytes is appended to the object's Unicode representation. Otherwise, the object's Unicode representation
is invalidated and converted to the UTF format, and bytes is appended to the object's new string
representation.
Tcl_AppendUnicodeToObj appends the Unicode string given by unicode and numChars to the object specified
by objPtr. If the object has an invalid Unicode representation, then unicode is converted to the UTF
format and appended to the object's string representation. Appends are optimized to handle repeated
appends relatively efficiently (it overallocates the string or Unicode space to avoid repeated
reallocations and copies of object'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 argument 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 │
constructed 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 prevents 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 command. 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 documentation 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 functionality 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_SUITABLE_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 │
long. │
long 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. │
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 functionality 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 object's string, then the string space is
reallocated 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 values. If the newLength argument is less than the current length
of the object's string, with objPtr->length is reduced without reallocating the string space; the
original allocated size for the string is recorded in the object, 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 allocated, it does not cause the Tcl interpreter to panic. Thus, if
newLength is greater than the space allocated for the object'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 object whose value is the space-separated concatenation
of the string representations of all of the objects 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 object 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 object whose ref count is zero.
SEE ALSO
Tcl_NewObj, Tcl_IncrRefCount, Tcl_DecrRefCount, format, sprintf
KEYWORDS
append, internal representation, object, object type, string object, string type, string representation,
concat, concatenate, unicode