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 \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 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.
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