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 ALSOTcl_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)
