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