Re: [OpenSCAD] How to detect chr(0)
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Re chr(0). Many systems use null terminated strings so chr(0) is treated as
the end of the string. I suspect this is the case here, but haven't looked
into the C RTL to confirm this.
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Well ignore what I said...
t = chr(0,41,42,43,44,255);
echo(t);
text(t);
for(i=[0:len(t)-1]) {
echo(t[i]);
translate([0,i*15,0]) text(t[i]);
}
Shows it if getting past the chr(0)
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t = chr(0,41,42,43,44,255);
echo(t);
text(t);
for(i=[0:len(t)-1]) {
echo(t[i]);
translate([0,i*15,0])
text(t[i]);
if(t[i]==chr(0))
echo("match 0");
if(t[i]==chr(255))
echo("match 255");
}
Hmmm...
Either a bug, or chr(0) plays a part in unicode or means something else...
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The chr() function is supposed to return valid unicode characters in utf-8
encoding, so for example "echo(chr(128512));" is valid and should give the
smiley character U+1F600.
Invalid input values will return an empty string, chr(0) is always treated
as invalid.
Note: This means that asking for chr(255) will internally result in the
bytes 0xc3 0xbf and not 0xff. As len() is also utf-8 aware, len(chr(255))
still returns 1 as it's one character.
ciao,
Torsten.
tp3 wrote
The chr() function is supposed to return valid unicode characters in utf-8
encoding, so for example "echo(chr(128512));" is valid and should give the
smiley character U+1F600.
Invalid input values will return an empty string, chr(0) is always treated
as invalid.
Note: This means that asking for chr(255) will internally result in the
bytes 0xc3 0xbf and not 0xff. As len() is also utf-8 aware, len(chr(255))
still returns 1 as it's one character.
ciao,
Torsten.
Hello and thanks for the input. I'm not sure what you mean by 'internally
result' but here's an example that shows that chr(255) does return a hex
value of 0xFF.
the_text = chr(255);
echo("number of characters = ",len(the_text));
for (i=[0:len(the_text)-1])
{
for (ascii_v = [0:255])
{
if (the_text[i] == chr(ascii_v)) :
{
if ((ascii_v) == 255):
{
xFF(count);
}
echo("character: ",the_text[i]);
echo("ASCII value:", ascii_v); // print the ascii
value being checked
}
}
}
ECHO: "number of characters = ", 1
ECHO: "character: ", "y"
ECHO: "ASCII value:", 255
Note that the character that prints like a y with two dots above it has the
hex value of 0xFF, not 0xC3 .0xBF.
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Sorry about those colons in the if statements. My cut&paste seemed to have
messed things up a bit.
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Your logic is a bit off there.
Basically your test is 'if(chr(255)==chr(255))'
Unfortunately, OpenSCAD doesn't (yet?) have a asc() function (or whatever
the unicode version would be called).
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HI Fantome. In OpenSCAD, a string is an array of Unicode "code points", it
isn't an array of bytes. Each code point in a string has a value between 1
and 0x10FFFF, except that some code point values are invalid. len(string)
is the number of code points in the string, and str[i] is the i'th code
point.
Torsten told you that internally, strings are represented in UTF-8 format.
But there are no operations in OpenSCAD that allow you to access that
internal representation. Numbers are represented internally as floating
point, but you can't access the underlying bit and byte patterns in a
float, either.
Your test program contains the word ASCII several times, but that's
misleading, you don't have access to the underlying byte representation.
On 16 April 2015 at 23:20, Fantome paul@brownsbrain.com wrote:
tp3 wrote
The chr() function is supposed to return valid unicode characters in
utf-8
encoding, so for example "echo(chr(128512));" is valid and should give
the
smiley character U+1F600.
Invalid input values will return an empty string, chr(0) is always
treated
as invalid.
Note: This means that asking for chr(255) will internally result in the
bytes 0xc3 0xbf and not 0xff. As len() is also utf-8 aware, len(chr(255))
still returns 1 as it's one character.
ciao,
Torsten.
Hello and thanks for the input. I'm not sure what you mean by 'internally
result' but here's an example that shows that chr(255) does return a hex
value of 0xFF.
the_text = chr(255);
echo("number of characters = ",len(the_text));
for (i=[0:len(the_text)-1])
{
for (ascii_v = [0:255])
{
if (the_text[i] == chr(ascii_v)) :
{
if ((ascii_v) == 255):
{
xFF(count);
}
echo("character: ",the_text[i]);
echo("ASCII value:", ascii_v); // print the ascii
value being checked
}
}
}
ECHO: "number of characters = ", 1
ECHO: "character: ", "y"
ECHO: "ASCII value:", 255
Note that the character that prints like a y with two dots above it has the
hex value of 0xFF, not 0xC3 .0xBF.
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MichaelAtOz wrote
Your logic is a bit off there.
Basically your test is 'if(chr(255)==chr(255))'
Unfortunately, OpenSCAD doesn't (yet?) have a asc() function (or whatever
the unicode version would be called).
Yes, thanks. This is really just an example that represents my code. The
actual code is many lines now. Basically it compares each character of
the_text to the values from 0 to 255. This is, as I'm sure everybody here
knows, the same as 0x00 to 0xFF. For example sake, I only included the
condition that finds the 0xFF. Once I clean up my code I'll post it here or
somewhere so people can enjoy it - tearing it apart or marveling at it.
Either way it will be working at that point. (chr(0) is only part not
working yet.)
... I should have pointed out that this code was only an example to show the
comparison and what it printed out.
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doug.moen wrote
HI Fantome. In OpenSCAD, a string is an array of Unicode "code points", it
isn't an array of bytes. Each code point in a string has a value between 1
and 0x10FFFF, except that some code point values are invalid. len(string)
is the number of code points in the string, and str[i] is the i'th code
point.
Torsten told you that internally, strings are represented in UTF-8 format.
But there are no operations in OpenSCAD that allow you to access that
internal representation. Numbers are represented internally as floating
point, but you can't access the underlying bit and byte patterns in a
float, either.
Your test program contains the word ASCII several times, but that's
misleading, you don't have access to the underlying byte representation.
Hello.
It's interesting to hear about the inner working of this. If OpenSCAD had
the ability to let users manipulate the bits the possibilities for modelling
objects and systems would be increased. Just my opinion of course.
When OpenScad echos/prints the chr(value), what it prints matches with the
ASCII chart. This is why I named the variable ASCII_value. I don't think
it's misleading. It is the ASCII value. It works for all 255 values, value 0
is the only one that is ignored by OpenSCAD.
For my specific application I guess I'll just figure out a work around since
it seems obvious now that OpenSCAD is treating chr(0) as a 'something' that
is not used in any comparison. The inner workings of OpenSCAD must have
checks for a NULL character or chr(0) that equates to 'jump to the next
character'. Oh well. One disappointment out of 256 values, still 99.61%
satisfaction.
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