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Tcl_StringObj(3) Tcl Library Procedures Tcl_StringObj(3)
____________________________________________________________________________________________________________
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
\7__\6__, use Tcl_ExternalToUtf to convert, or Tcl_New-ByteArrayObj Tcl_NewByteArrayObj
ByteArrayObj if the string is a collection of uninter-preted uninterpreted
preted bytes.)
int length (in) The number of bytes to copy from bytes when initializ-ing, initializing,
ing, setting, or appending to a string object. If neg-ative, negative,
ative, all bytes up to the first null are used.
const Tcl_UniChar *unicode (in) Points to the first byte of an array of Unicode charac-ters characters
ters 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 representa-tion. representation.
tion.
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 trunca-tion. truncation.
tion. If NULL is passed then the suffix "..." is used.
const char *format (in) Format control string including % conversion speci-fiers. specifiers.
fiers.
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 includ-ing including
ing 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 inter-preter's interpreter's
preter'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_Set-StringObj Tcl_SetStringObj
StringObj and Tcl_SetUnicodeObj free any old string representation as well as any old internal repre-sentation representation
sentation 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 refer-enced referenced
enced 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 pur-pose, purpose,
pose, 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 copy-onwrite
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 represen-tation representation
tation 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 speci-fied specified
fied 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 (which-ever (whichever
ever 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 inter-nal internal
nal 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 vari-able variable
able 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 proce- |
dure 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 dur- |
ing 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 dif- |
fer. 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 cur-rent current
rent 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 indi-cate indicate
cate 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 concatena-tion concatenation
tion 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 representa-tion, representation,
tion, concat, concatenate, unicode
Tcl 8.1 Tcl_StringObj(3)
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