:   '''`[encoding] convertfrom`''' ?''encoding''? ''string''

The lower 8-bits of each character in ''string'' are taken as a single byte and
the resulting sequence of bytes is converted from ''encoding'' to a [Unicode]
string.  If ''encoding'' is not specified, the [encoding system%|%system
encoding] is used.



** Invalid Data **

[PYK] 2017-08-19: If a string to be converted from `utf-8` contains invalid
utf-8 byte sequences, each invalid byte is interpreted as an 8-bit integer and
converted to the unicode character at that code point. I.e., `encoding
convertfrom utf-8` will never fail, so it can not be used to determine whether
a string is valid utf-8.

======
set value [binary format c 239]
set value [encoding convertfrom utf-8 $value]
scan $value %c codepoint ; # $codepoint == 239
======

For comparison, here is the same operation on a valid utf-8 sequence: 

======
set value [binary format ccc 239 188 129]
set value [encoding convertfrom utf-8 $value]
scan $value %c codepoint ; # $codepoint == 65281
======


`[ycl%|%ycl string encode]` and `[ycl%|%ycl string decode]` are implementations
that return an error if the string can not be faithfully encoded/decoded. 



** Fonts and Encodings **

[MG]: I have a bit of a strange problem, hopefully someone can help. This example script shows what I'm trying to do - it displays cp437-encoded text in a [text] widget:


======
text .t -font Term
pack .t
.t insert end [format %c 152]
.t insert end [encoding convertfrom cp437 [format %c 152]]
======


The Term font being used is available at http://8bit.memoryleak.org/Flag/Term.ttf and is designed for displaying cp437-encoded text.

Character 152 in cp437 is a y-umlaut. However, the first insert displays a placeholder character (a solid down-arrow) instead. The second does display a y-umlaut, but it does so by mapping to character 255, which isn't available in the Term font (because it has no meaning in cp437), so Tcl uses a fallback font, and it looks totally wrong (Term is fixed-width and quite bold; the fallback font, Lucida Sans Unicode, doesn't match up at all).

I can use the Term font in other (non-Tcl) applications, for instance MS Word, and insert char 152, which gives a y-umlaut without any problem. I honestly have no idea what's causing this issue; can anyone shed any light?


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