For example:
x := #123;
I tried to search around Google but I simply have no idea what this means.
IIRC it means a character value of the number (eg. #32 -> space).
#123 is a character (Char type) of the ordinal value 123.
It's character code. #97 is equivalent to 'a' etc etc
A chart can be see here.
It is an extention to standard Pascal, Borland Pascal accepts the pound sign ('#') followed immediately by a decimal number between 0 and 255 as a single character with that code.
As other have mentioned it's a character code, I most often see them used for line breaks in messages, or other control character such as Tab (#9)
ShowMessage('Error:'#13#10'Something terrible happened')
Strangely it's not necessary to concatinate a string involving these.
It's character code. #97 is equivalent to chr(97) etc etc
Related
well i was reading some common concepts regarding parsing in compiler..i came across look ahead and read ahead symbol i search and read about them but i am stuck like why we need both of them ? would be grateful for any kind suggestion
Lookahead symbol: when node being considered in parse tree is for a terminal, and the
terminal matches lookahead symbol,then we advance in both parse and
input
read aheadsymbol: lexical analyzer may need to read some character
before it can decide on the token to be returned
One of these is about parsing and refers to the next token to be produced by the lexical scanner. The other one, which is less formal, is about lexical analysis and refers to the next character in the input stream. It should be clear which is which.
Note that while most parsers only require a single lookahead token, it is not uncommon for lexical analysis to have to backtrack, which is equivalent to examining several unconsumed input characters.
I hope I got your question right.
Consider C.
It has several punctuators that begin the same way:
+, ++, +=
-, --, -=, ->
<, <=, <<, <<=
...
In order to figure out which one it is when you see the first + or - or <, you need to look ahead one character in the input (and then maybe one more for <<=).
A similar thing can happen at a higher level:
{
ident1 ident2;
ident3;
ident4:;
}
Here ident1, ident3 and ident4 can begin a declaration, an expression or a label. You can't tell which one immediately. You can consult your existing declarations to see if ident1 or ident3 is already known (as a type or variable/function/enumeration), but it's still ambiguous because a colon may follow and if it does, it's a label because it's permitted to use the same identifier for both a label and a type/variable/function/enumeration (those two name spaces do not intersect), e.g.:
{
typedef int ident1;
ident1 ident2; // same as int ident2
int ident3 = 0;
ident3; // unused expression of value 0
ident1:; // unused label
ident2:; // unused label
ident3:; // unused label
}
So, you may very well need to look ahead a character or a token (or "unread" one) to deal with situations like these.
Hi I've been struggling with this for the last hour and am no closer. How exactly do I strip everything except numbers, commas and decimal points from a rails string? The closest I have so far is:-
rate = rate.gsub!(/[^0-9]/i, '')
This strips everything but the numbers. When I try add commas to the expression, everything is getting stripped. I got the aboves from somewhere else and as far as I can gather:
^ = not
Everything to the left of the comma gets replaced by what's in the '' on the right
No idea what the /i does
I'm very new to gsub. Does anyone know of a good tutorial on building expressions?
Thanks
Try:
rate = rate.gsub(/[^0-9,\.]/, '')
Basically, you know the ^ means not when inside the character class brackets [] which you are using, and then you can just add the comma to the list. The decimal needs to be escaped with a backslash because in regular expressions they are a special character that means "match anything".
Also, be aware of whether you are using gsub or gsub!
gsub! has the bang, so it edits the instance of the string you're passing in, rather than returning another one.
So if using gsub! it would be:
rate.gsub!(/[^0-9,\.]/, '')
And rate would be altered.
If you do not want to alter the original variable, then you can use the version without the bang (and assign it to a different var):
cleaned_rate = rate.gsub!(/[^0-9,\.]/, '')
I'd just google for tutorials. I haven't used one. Regexes are a LOT of time and trial and error (and table-flipping).
This is a cool tool to use with a mini cheat-sheet on it for ruby that allows you to quickly edit and test your expression:
http://rubular.com/
You can just add the comma and period in the square-bracketed expression:
rate.gsub(/[^0-9,.]/, '')
You don't need the i for case-insensitivity for numbers and symbols.
There's lots of info on regular expressions, regex, etc. Maybe search for those instead of gsub.
You can use this:
rate = rate.gsub!(/[^0-9\.\,]/g,'')
Also check this out to learn more about regular expressions:
http://www.regexr.com/
Wondering if it's possible to print a carriage return without a line feed in erlang? i.e. equivalent to printf("this will be replaced next time \r"); in C.
Had a look through the io:format() documentation and didn't see anything. It only seems to support ~n, equivalent to carriage return+line feed pair ('\n' in C).
Thx.
"\r" is a perfectly valid escape sequence in Erlang. So you can do just
io:format("\r").
Check the reference manual for other escape sequences.
You can use \r in a string for the return character so:
io:format("Counter value: ~b\r", [Counter])
This is also works for character constants, $\r, and in quoted atoms.
Doh. Answer came almost as soon as I posted. ~c enables printing of ASCII characters, so it's just a case of printing ASCII carriage return (13). e.g.
io:format("Counter value: ~b~c", [Counter,13])
Still interested in anything more elegant...
Thx.
I've seen this posted a couple of times but none of the solutions seem to work for me so far...
I'm trying to remove a spurious  character from a string...
e.g.
"myÂstring here Â$100"
..but it should be my string here $100
I've tried:
string.gsub(/\194/,'')
string.gsub(194.chr,'')
string.delete 194.chr
All of these still leave the  intact..
Any thoughts?
By default, Rails supports UTF-8.
You can use your favorite editor to write a gsub call using the proper character you want to replace, as in:
"myÂstring here Â$100".gsub(/Â/,"")
If this does not work as well, you might be having an encoding error somewhere on your stack, probably on your HTML document. Try running rails console, extract somehow that string (if it comes from the Model, try to perform a find on the containing class) and run the gsub. It won't solve your problem, but you'll get a clue to where exactly the problem may lie.
Looks like a character encoding problem to me. For every Unicode code point in the range U+0080..U+00BF inclusive, the UTF-8 encoding is a two-byte sequence, 0xC2 (194 decimal) and the numeric value the code point. For example, a non-breaking space--U+00A0--becomes 0xC2 0xA0. Was there another extra character in there, that you already removed?
At any rate, gsub(/\194/,'') is wrong. \nnn is supposed to be an octal escape, but the number is in its decimal form. 194 in octal is \302.
"myÂstring here Â$100".gsub("Â","") # "mystring here $100"
Is that what you meant?
Could anybody help me make a proper regular expression from a bunch of text in Ruby. I tried a lot but I don't know how to handle variable length titles.
The string will be of format <sometext>title:"<actual_title>"<sometext>. I want to extract actual_title from this string.
I tried /title:"."/ but it doesnt find any matches as it expects a closing quotation after one variable from opening quotation. I couldn't figure how to make it check for variable length of string. Any help is appreciated. Thanks.
. matches any single character. Putting + after a character will match one or more of those characters. So .+ will match one or more characters of any sort. Also, you should put a question mark after it so that it matches the first closing-quotation mark it comes across. So:
/title:"(.+?)"/
The parentheses are necessary if you want to extract the title text that it matched out of there.
/title:"([^"]*)"/
The parentheses create a capturing group. Inside is first a character class. The ^ means it's negated, so it matches any character that's not a ". The * means 0 or more. You can change it to one or more by using + instead of *.
I like /title:"(.+?)"/ because of it's use of lazy matching to stop the .+ consuming all text until the last " on the line is found.
It won't work if the string wraps lines or includes escaped quotes.
In programming languages where you want to be able to include the string deliminator inside a string you usually provide an 'escape' character or sequence.
If your escape character was \ then you could write something like this...
/title:"((?:\\"|[^"])+)"/
This is a railroad diagram. Railroad diagrams show you what order things are parsed... imagine you are a train starting at the left. You consume title:" then \" if you can.. if you can't then you consume not a ". The > means this path is preferred... so you try to loop... if you can't you have to consume a '"' to finish.
I made this with https://regexper.com/#%2Ftitle%3A%22((%3F%3A%5C%5C%22%7C%5B%5E%22%5D)%2B)%22%2F
but there is now a plugin for Atom text editor too that does this.