Provided by: tcl9.0-doc_9.0.1+dfsg-1_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_AppendLimitedToObj, Tcl_Format, Tcl_AppendFormatToObj, Tcl_ObjPrintf, Tcl_AppendPrintfToObj,
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)
int
Tcl_GetUniChar(objPtr, index)
Tcl_Size
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_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 embedded null characters unless numChars is
negative. (Applications needing null bytes should
represent them as the two-byte sequence \300\200, use
Tcl_ExternalToUtf to convert, or Tcl_NewByteArrayObj if the
string is a collection of uninterpreted bytes.)
Tcl_Size length (in) The number of bytes to copy from bytes when initializing,
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 contain embedded null characters unless numChars is
negative.
Tcl_Size numChars (in) The number of Unicode characters to copy from unicode when
initializing, setting, or appending to a string value. If
negative, all characters up to the first null character are
used.
Tcl_Size index (in) The index of the Unicode character to return.
Tcl_Size first (in) The index of the first Unicode character in the Unicode
range to be returned as a new value. If negative, behave
the same as if the value was 0.
Tcl_Size last (in) The index of the last Unicode character in the Unicode
range to be returned as a new value. If negative, take all
characters up to the last one available.
Tcl_Obj *objPtr (in/out) A pointer to a value to read, or to an unshared value to
modify.
Tcl_Obj *appendObjPtr (in) The value to append to objPtr in Tcl_AppendObjToObj.
Tcl_Size | int *lengthPtr (out) The location where Tcl_GetStringFromObj will store the
length of a value's string representation. May be
(Tcl_Size *)NULL when not used. If it points to a variable
which type is not Tcl_Size, a compiler warning will be
generated. If your extensions is compiled with
-DTCL_8_API, this function will panic for strings with more
than INT_MAX bytes/characters, otherwise expect it to
crash.
const char *string (in) Null-terminated string value to append to objPtr.
Tcl_Size 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.
Tcl_Size objc (in) The number of elements to format or concatenate.
Tcl_Obj *objv[] (in) The array of values to format or concatenate.
Tcl_Size 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
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 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 procedures set the value 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
value.
Tcl_GetStringFromObj and Tcl_GetString return a value'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 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 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 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. If the index is out
of range it returns -1;
Tcl_GetRange returns a newly created value comprised of the characters between first and last (inclusive)
in the value's Unicode representation. If the value's Unicode representation is invalid, the Unicode
representation is regenerated from the value's string representation. If first is negative, then the
returned string starts at the beginning of the value. If last negative, then the returned string ends at
the end of the value.
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
convert bytes 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. Eventually buffer growth is done by large allocations to optimize multiple calls.
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 (char *)NULL
to indicate the end of the 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 negative, 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);
Tcl_DecrRefCount(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 but the behavior is as similar as possible to sprintf. The "hh"
and (Microsoft-specific) "w" format specifiers are not supported. The "L" format specifier means that an
"mp_int *" argument is expected (or a "long double" in combination with [aAeEgGaA]). 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 protection may be provided by some compilers.
Tcl_AppendPrintfToObj is an appending alternative form of Tcl_ObjPrintf with functionality equivalent to
Tcl_Obj *newPtr = Tcl_ObjPrintf(format, ...);
Tcl_AppendObjToObj(objPtr, newPtr);
Tcl_DecrRefCount(newPtr);
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 value'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 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 allocated, 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.
REFERENCE COUNT MANAGEMENT
Tcl_NewStringObj, Tcl_NewUnicodeObj, Tcl_Format, Tcl_ObjPrintf, and Tcl_ConcatObj always return a zero-
reference object, much like Tcl_NewObj.
Tcl_GetStringFromObj, Tcl_GetString, Tcl_GetUnicodeFromObj, Tcl_GetUnicode, Tcl_GetUniChar,
Tcl_GetCharLength, and Tcl_GetRange all only work with an existing value; they do not manipulate its
reference count in any way.
Tcl_SetStringObj, Tcl_SetUnicodeObj, Tcl_AppendToObj, Tcl_AppendUnicodeToObj, Tcl_AppendObjToObj,
Tcl_AppendStringsToObj, Tcl_AppendStringsToObjVA, Tcl_AppendLimitedToObj, Tcl_AppendFormatToObj,
Tcl_AppendPrintfToObj, Tcl_SetObjLength, and Tcl_AttemptSetObjLength and require their objPtr to be an
unshared value (i.e, a reference count no more than 1) as they will modify it.
Additional arguments to the above functions (the appendObjPtr argument to Tcl_AppendObjToObj, values in
the objv argument to Tcl_Format, Tcl_AppendFormatToObj, and Tcl_ConcatObj) can have any reference count,
but reference counts of zero are not recommended.
Tcl_Format and Tcl_AppendFormatToObj may modify the interpreter result, which involves changing the
reference count of a value.
SEE ALSO
Tcl_NewObj(3tcl), Tcl_IncrRefCount(3tcl), Tcl_DecrRefCount(3tcl), format(3tcl), sprintf(3)
KEYWORDS
append, internal representation, value, value type, string value, string type, string representation,
concat, concatenate, unicode
Tcl 8.1 Tcl_StringObj(3tcl)