Tcl_StringObj(3) Tcl Library Procedures Tcl_StringObj(3)
Tcl_NewStringObj, Tcl_NewUnicodeObj, Tcl_SetStringObj, Tcl_SetUnicodeObj, Tcl_Get-
StringFromObj, Tcl_GetString, Tcl_GetUnicodeFromObj, Tcl_GetUnicode, Tcl_GetUniChar,
Tcl_GetCharLength, Tcl_GetRange, Tcl_AppendToObj, Tcl_AppendUnicodeToObj, Tcl_Append-
StringsToObj, Tcl_AppendStringsToObjVA, Tcl_AppendObjToObj, Tcl_SetObjLength, Tcl_Conca-
tObj, Tcl_AttemptSetObjLength - manipulate Tcl objects as strings
Tcl_SetStringObj(objPtr, bytes, length)
Tcl_SetUnicodeObj(objPtr, unicode, numChars)
Tcl_GetRange(objPtr, first, last)
Tcl_AppendToObj(objPtr, bytes, length)
Tcl_AppendUnicodeToObj(objPtr, unicode, numChars)
Tcl_AppendStringsToObj(objPtr, string, string, ... (char *) NULL)
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 should not |
contain embedded null bytes unless length 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 |
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 Uni-
code characters used to set or append to a
string object. This byte array may contain
embedded null characters unless numChars is
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 charac-
ter are used.
int index (in) The index of the Unicode character to
int first (in) The index of the first Unicode character in
the Unicode range to be returned as a new
int last (in) The index of the last Unicode character in
the Unicode range to be returned as a new
Tcl_Obj *objPtr (in/out) Points to an object to manipulate.
Tcl_Obj *appendObjPtr (in) The object to append to objPtr in Tcl_Appen-
int *lengthPtr (out) If non-NULL, the location where Tcl_Get-
StringFromObj will store the the length of
an object's string representation.
CONST char *string (in) Null-terminated string value to append to
va_list argList (in) An argument list which must have been ini-
tialised using TCL_VARARGS_START, and
cleared using va_end.
int newLength (in) New length for the string value of objPtr,
not including the final null character.
int objc (in) The number of elements to concatenate.
Tcl_Obj *objv (in) The array of objects to concatenate.
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 doesn't 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_SetUni-
codeObj 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
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 lim-
ited 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 repre-
sentation. 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 pro-
cedure 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 repre-
sentation is invalid, the Unicode representation is regenerated from the object's string
Tcl_GetCharLength returns the number of characters (as opposed to bytes) in the string
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 suc-
cessful, then the converted form of bytes is appended to the object's Unicode representa-
tion. 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
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
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 pro-
vided, 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 tak-
ing a variable number of arguments it takes an argument list.
The Tcl_SetObjLength procedure changes the length of the string value of its objPtr argu-
ment. 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 val-
ues. 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 allo-
cated 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 suffi-
cient memory to satisfy the request cannot be allocated, it does not cause the Tcl inter-
preter 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_AttemptSetOb-
jLength 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 repre-
sentations 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.
Tcl_NewObj, Tcl_IncrRefCount, Tcl_DecrRefCount
append, internal representation, object, object type, string object, string type, string
representation, concat, concatenate, unicode
Tcl 8.1 Tcl_StringObj(3)