'''string bytelength''' ''string''



** See Also **

   [string]:   

   [string length]:   



** Description **

Returns a decimal string giving the number of bytes used to represent
''string'' in memory.  Because UTF-8 uses one to three bytes to represent
Unicode characters, the byte length will not be the same as the character
length in general. The cases where a script cares about the byte length are
rare.  Refer to the '''Tcl_NumUtfChars''' manual entry for more details on the
UTF-8 representation.

'''In almost all cases, you should use the '''[string length]''' operation
(including determining the length of a Tcl ByteArray object).'''  An example on
[tcom] purports to need [[`string bytelength`] when generating a binary blob to
get the length of the blob without forcing generation of an internal string
representation by [[`[string length]`], but [[`[string length]`] does not force
an internal string representation when the internal object is a pure bytearray
representation.

[['''string bytelength''']] should '''not''' be used with binary data.  This
command measures how long the UTF-8 representation of a string is in bytes.
For binary data you don't want conversion to UTF-8, so you don't want
[['''string bytelength''']] either.  Use [['''[string length]''']] instead.

[US]: Proof for the sceptical:

======
for {set n 0} {$n < 256} {incr n} {
  lappend cl $n
}
set str [binary format c* $cl]
puts "len : [string length $str]"
puts "blen: [string bytelength $str]"
======

[DKF]: It's not even real UTF-8. It's the length of Tcl's internal encoding
which is ''almost''-UTF8 (i.e., it is consistently denormalized in certain
ways). The only possible use of '''string bytelength''' is answering the
question “How much memory is allocated to hold this value's `bytes` field?”



** Basic Example **

======
string bytelength abc ;# -> 3
======



** Questions **

[AMG]: "UTF-8 uses one to three bytes to represent Unicode characters."  This is true only for the BMP.  For characters above FFFF, UTF-8 characters can be up to six bytes each.  Does Tcl support such yet?

[DKF]: No. This is one of the things we plan to fix in Tcl 9.0.

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