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< Erlang ~ String parser |
| phicarre |
 Posted: Thu Mar 26, 2009 3:38 pm |
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Joined: 23 Mar 2009
Posts: 14
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I am looking for a string parser in erlang. Any idea ?
My string will be a list of fields separated by a comma. |
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| uwiger |
| Posted: Fri Mar 27, 2009 1:22 pm |
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User
Joined: 03 Jul 2006
Posts: 604
Location: Sweden
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phicarre wrote: I am looking for a string parser in erlang. Any idea ?
My string will be a list of fields separated by a comma.
A very simple way to parse something like this is
Code: Lines = string:tokens(Str, [$\n]),
[string:tokens(L, [$,]) || L <- Lines]
...assuming that the string consists of lines of comma-separated values. Otherwise, skip the first step.
Erlang (BEAM) emulator version 5.6.5 [smp:2] [async-threads:0]
Code: Eshell V5.6.5 (abort with ^G)
1> Str = "15,16,17".
"15,16,17"
2> string:tokens(Str,[$,]).
["15","16","17"]
The call can also be written string:tokens(Str,","). |
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| phicarre |
| Posted: Fri Mar 27, 2009 4:40 pm |
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Joined: 23 Mar 2009
Posts: 14
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Ok, but I would like to extract each token by supposing
[field1,field2,field3] then
field1 = 15
field2 = 16
field3 = 17 |
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| phicarre |
| Posted: Fri Mar 27, 2009 6:55 pm |
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Joined: 23 Mar 2009
Posts: 14
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I read a little bit the doc and it suggests to represent a string as a bit stream because of the memory.
Then my question must be changed:
I have a bit stream and I want to extract from it fields separated by a comma.
S="hello,how,are,you".
How to interpret it as <<field1,field2,field3>> and after how to use each field.
if field1=hello ... |
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| prof3ta |
| Posted: Mon Apr 20, 2009 12:55 pm |
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Joined: 06 Feb 2009
Posts: 34
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Something like this?
Code:
-module(parser).
-export([parse/1]).
parse(String) when is_list(String) ->
Binary = list_to_binary(String),
parse(Binary, [], []);
parse(Binary) when is_binary(Binary) ->
parse(Binary, [], []).
parse(<<>>, Acc, Tokens) ->
lists:reverse([lists:reverse(Acc)|Tokens]);
parse(<<$,,Rest/binary>> = Binary, Acc, Tokens) when is_binary(Binary) ->
parse(Rest, [], [lists:reverse(Acc)|Tokens]);
parse(<<Head, Rest/binary>> = Binary, Acc, Tokens) when is_binary(Binary) ->
parse(Rest, [Head|Acc], Tokens).
This code will consider empty terms as well, so that will return:
from:
Code: parser:parse("s,,t").
And:
from:
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Last edited by prof3ta on Mon Apr 20, 2009 1:02 pm; edited 1 time in total |
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| prof3ta |
| Posted: Mon Apr 20, 2009 1:00 pm |
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Joined: 06 Feb 2009
Posts: 34
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By the way, if you already know the "meaning and the size of the fields" that you have in your binary (for example, if you're parsing a well known protocol), you can always do something like:
Code:
case Packet of
<<Id:8, Name:256, Surname:256, Rest/binary>> ->
...
In this case you will have your values bounded to your variables, ready to use. |
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| wuji |
| Posted: Sat Aug 11, 2012 2:15 am |
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Joined: 10 Aug 2012
Posts: 654
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| dongdongwu |
| Posted: Thu Sep 20, 2012 5:34 am |
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