Tcl_StringObj(3) Tcl Library Procedures Tcl_StringObj(3)

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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.
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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. If first < 0, then the returned string starts at the
beginning of the value. If last < 0, 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_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 but the
behavior is as similar as possible to sprintf. Format specifiers
which were added by C99 (like "hh", "ll", "j", "z", "t", "L") are not
supported. 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(3), Tcl_IncrRefCount(3), Tcl_DecrRefCount(3), format(n),
sprintf(3)

KEYWORDS

append, internal representation, value, value type, string value,
string type, string representation, concat, concatenate, unicode

Tcl 8.1 Tcl_StringObj(3)