vb.net - How to find all occurrences of specific string in long text -

i have long text (e.g. information many books) in 1 string , in 1 line.

i want find isbn (only number - each number prevents chars isbn). found code how extract number on first position. problem how create loop text. can use example streamreader? thank answers.

example:

sub main()     dim getliteratura string = "'author 1. name of book 1. isbn 978-80-251-2025-5.', 'author 2. name of book 2. isbn 80-01-01346.', 'author 3. name of book. isbn 80-85849-83.'"     dim test integer = getliteratura.indexof("isbn")     dim getisbn string = getliteratura.substring(test + 5, getliteratura.indexof(".", test + 1) - test - 5)      console.write(getisbn)     console.readkey() end sub 

since can pass start position indexof method, can loop through string starting search last iteration left off. instance:

dim getliteratura string = "'author 1. name of book 1. isbn 978-80-251-2025-5.', 'author 2. name of book 2. isbn 80-01-01346.', 'author 3. name of book. isbn 80-85849-83.'" dim isbns new list(of string)() dim position integer = 0 while position <> -1     position = getliteratura.indexof("isbn", position)     if position <> -1         dim endposition integer = getliteratura.indexof(".", position + 1)         if endposition <> -1             isbns.add(getliteratura.substring(position + 5, endposition - position - 5))         end if         position = endposition     end if end while 

that efficient of method find, if data loaded string. however, method not readable or flexible. if things concern more mere efficiency, may want consider using regex:

for each match in regex.matches(getliteratura, "isbn (?<isbn>.*?)\.")     isbns.add(i.groups("isbn").value) next 

as can see, not easier read, configurable. store pattern externally in resource, configuration file, database, etc.

if data isn't loaded string, , efficiency utmost concern, may want using stream reader load small subset of data memory @ once. logic bit more complicated, still not overly difficult.

here's simple example of how via streamreader:

dim isbns new list(of string)() using reader streamreader = new streamreader(stream)     dim builder new stringbuilder()     dim isbnregex new regex("isbn (?<isbn>.*?)\.")     while not reader.endofstream         dim charvalue integer = reader.read()         if charvalue <> -1             builder.append(convert.tochar(charvalue))             dim matches matchcollection = isbnregex.matches(builder.tostring())             if matches.count <> 0                 each match in matches                     isbns.add(i.groups("isbn").value)                 next                 builder.clear()             end if         end if     end while end using 

as can see, in example, match found, adds list , clears out builder being used buffer. way, amount of data being held in memory @ 1 time never more size of 1 "record".

update

since, based on comments, you're having trouble getting work properly, here full working sample outputs just isbn numbers, without of surrounding characters. create new vb.net console application , paste in following code:

imports system.text.regularexpressions  module module1     public sub main()         dim data string = "'author 1. name of book 1. isbn 978-80-251-2025-5.', 'author 2. name of book 2. isbn 80-01-01346.', 'author 3. name of book. isbn 80-85849-83.'"         each string in getisbns(data)             console.writeline(i)         next         console.readkey()     end sub      public function getisbns(data string) list(of string)         dim isbns new list(of string)()         each match in regex.matches(data, "isbn (?<isbn>.*?)\.")             isbns.add(i.groups("isbn").value)         next         return isbns     end function end module