Provided by: tcl8.6-doc_8.6.12+dfsg-1build1_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 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
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.)
int 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.
int 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.
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_AppendObjToObj.
int *lengthPtr (out) If non-NULL, the location where
Tcl_GetStringFromObj 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
initialized 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 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. The
index is assumed to be in the appropriate range.
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.
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 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 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);
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 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 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.
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