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  • Postfix and right-associative operators in LR(0) parsers

    - by Ian
    Is it possible to construct an LR(0) parser that could parse a language with both prefix and postfix operators? For example, if I had a grammar with the + (addition) and ! (factorial) operators with the usual precedence then 1+3! should be 1 + 3! = 1 + 6 = 7, but surely if the parser were LR(0) then when it had 1+3 on the stack it would reduce rather than shift? Also, do right associative operators pose a problem? For example, 2^3^4 should be 2^(3^4) but again, when the parser have 2^3 on the stack how would it know to reduce or shift? If this isn't possible is there still a way to use an LR(0) parser, possibly by converting the input into Polish or Reverse Polish notation or adding brackets in the appropriate places? Would this be done before, during or after the lexing stage?

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  • Linq: comparison with nonexisting value should not cause the exception, but it does

    - by Seacat
    Hello, Given I don't know if the parameter will be null or not and I want to use it in the following way: if Param != null then compare with its id if Param == null then compare with null. Something like that: var c = from cat in context.Categories where ParamCat != null && cat.ParentId == ParamCat.Id || ParamCat == null && cat.ParentId == null select c; If ParamCat is null as soon as I try to get something from c (for example c.Count()) it throws the exception. Usually when we use some kind of condition it stop comparison as soon as condition fail especially if we use AND. For example this code will not cause any exception: if (ParamCat != null && cat.ParentId == RaramCat.Id) { } If so, why the linq code above throw exception? (Null reference) Thanks

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  • String useless character strip - PHP

    - by Zoltan Repas
    Hi! I've got a huge problem. I made a special ID for the things in our webpage. Let's see an example: H0059 - this is the special ID called registration number. The last two chars are the things' id. I'd like to cut off the useless characters, to get the real ID, what means strip the first char, and all the 0s before any other numbers. (Example: L0745 = 745, V1754 = 1754, L0003 = 3, B0141 = 141, P0040 = 40, V8000 = 8000) Please help me in this. I've tried with strreplace and explode but failed :( Thanks for the help.

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  • How to hash and check for equality of objects with circular references

    - by mfya
    I have a cyclic graph-like structure that is represented by Node objects. A Node is either a scalar value (leaf) or a list of n=1 Nodes (inner node). Because of the possible circular references, I cannot simply use a recursive HashCode() function, that combines the HashCode() of all child nodes: It would end up in an infinite recursion. While the HashCode() part seems at least to be doable by flagging and ignoring already visited nodes, I'm having some troubles to think of a working and efficient algorithm for Equals(). To my surprise I did not find any useful information about this, but I'm sure many smart people have thought about good ways to solve these problems...right? Example (python): A = [ 1, 2, None ]; A[2] = A B = [ 1, 2, None ]; B[2] = B A is equal to B, because it represents exactly the same graph. BTW. This question is not targeted to any specific language, but implementing hashCode() and equals() for the described Node object in Java would be a good practical example.

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  • Problems getting PowerPoint Combobox to list items correctly

    - by mike toyn
    I am creating a PowerPoint in which I want users to be able to select an item from a list in a combo box. Nothing needs to happen after this, it is just to provide a record, on screen, of their choice. My problem is that I seem to either be able to populate the combo box and users can select an item but the list gets longer each time the combobox is clicked on (i.e each time it is clicked on the list gets duplicated). Or alternatively, I can clear the combo box, then populate it but in this scenario, the users choice also seems to get cleared. VBA example 1: Private Sub ComboBox1_DropButtonClick() With ComboBox1 .AddItem " ", 0 .AddItem "speed", 1 .AddItem "provisionality", 2 .AddItem "automation", 3 .AddItem "replication", 4 .AddItem "communicability", 5 .AddItem "multi-modality", 6 .AddItem "non-linearity", 7 .AddItem "capacity", 8 .AddItem "interactivity", 9 End With End Sub VBA example 2: Private Sub ComboBox1_DropButtonClick() ComboBox1.Clear With ComboBox1 .AddItem " ", 0 .AddItem "speed", 1 .AddItem "provisionality", 2 .AddItem "automation", 3 .AddItem "replication", 4 .AddItem "communicability", 5 .AddItem "multi-modality", 6 .AddItem "non-linearity", 7 .AddItem "capacity", 8 .AddItem "interactivity", 9 End With End Sub Can anyone help?

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  • C++ Interpreter: How to emit error messages?

    - by Rawr
    I want to emit dynamic error messages like all interpreters do nowadays, for example: Name error: Undefined variable would be constant, however what I want to reach is: Name error: Undefined variable 'X', in line 1 Okay. The line number was really no problem: Every error message must have a line number, so I added it to the error emitter function: Error( ErrType type, string msg, int line ); So where is my problem? How do I get the 'X' into Undefined variable *? I can't use sprintf as it doesn't support strings yet I use them everywhere I can't simply use cout and connect everything as I want error messages to be supressable I'd like to get everything into one function like above, Error() How do I put together dynamic error messages? For example: Error( Name, sprintf("Undefined variable %s", myVariableName ), lineNum ); (But myVariableName is a string and sprintf will mess things up)

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  • Encrypting password in compiled C or C++ code

    - by Daniel
    Hello!, I know how to compile C and C++ Source files using GCC and CC in the terminal, however i would like to know if its safe to include passwords in these files, once compiled. For example.. i check user input for a certain password e.g 123, but it appears compiled C/C++ programs is possible to be decompiled. Is there anyway to compile a C/C++ source file, while keeping the source completely hidden.. If not, could anyone provide a small example of encrypting the input, then checking against the password e.g: (SHA1, MD5)

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  • Select an entity according to a list of associated entities

    - by Maverickch
    I have the following database schema : Two tables, books and tags, with n-m relationship. Books - Tags We can have for example the book 1, with tags {A,B,C}, and book 2, with tags {A}. I would like to select the books according to a list of tags. For example : selected tags list : {A,B} - book 1 My idea was to use the MINUS SQL function, to subtract book tags list to the selected tags list, and return the book if the list was empty. Unfortunately, this SQL function is not supported by HQL. Any idea about that ?

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  • How to host your own http-like server using ServiceHost?

    - by Ole Jak
    I use ServiceHost for hosting WCF cervices. I want to host near to my WCF services my own tcp programm (like WCF service but with out WCF) for direct sockets operations (like lien to some sort of broadcasting TCP stream) I want to use ServiceHost for somehow simplyfiing proces of creating my TCP sender\listener, to somehow control namespaces (so I would be able to let my clients to send TCP streams directly into my service using some nice URLs like www.example.com:34123/myserver/stream?id=1 or www.example.com:34123/myserver/stream?id=222 and so that I will not be bothered with Idea of 1 client for 1 socket at one time moment, BTW I realy want to keep my WCF services on the same port as my own server or what it is...) Can any body please hrlp me with this?

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  • geom_rect and NULL

    - by csgillespie
    I've been looking at the geom_rect example in section 5.10 of the ggplot2 book and don't understand the purpose of the NULL's in the aes function. For example, using the mpg data: g = ggplot(data=mpg, aes(x=displ, y=hwy)) + geom_point() #Produces a plot with a transparent filled region g + geom_rect(aes(NULL, NULL), alpha=0.1,xmin=5, xmax=7, ymin=10, ymax=45, fill="blue") #Solid filled region (v0.9) or nothing in v0.8 g + geom_rect(alpha=0.1,xmin=5, xmax=7, ymin=10, ymax=45, fill="blue") My understanding is that the NULL's are resetting the x & y mapping, but I don't see why this should affect the transparency.

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  • Is is possible to intercept a constructor on a class you do not own?

    - by code poet
    Referring to my possible answer to this question: http://stackoverflow.com/questions/2907535/how-would-you-audit-asp-net-membership-tables-while-recording-what-user-made-the/2911616#2911616 Is it possible to intercept a call, coming from code you do not own, to a ctor on a sealed internal class that you do not own with the intention of manipulating the object before returning? Concrete example: SqlMembershipProvider, for all of it's data access, instantiates a connection helper class, System.Web.DataAccess.SqlConnectionHolder. The desired result is to intercept this instantiation and perform an operation on the public connection that is opened in the ctor of System.Web.DataAccess.SqlConnectionHolder before letting execution continue. Is this possible. If so, an brief example would be appreciated.

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  • Horizontally Flip a One Bit Bitmap Line

    - by roygbiv
    I'm looking for an algorithm to flip a 1 Bit Bitmap line horizontally. Remember these lines are DWORD aligned! I'm currently unencoding an RLE stream to an 8 bit-per-pixel buffer, then re-encoding to a 1 bit line, however, I would like to try and keep it all in the 1 bit space in an effort to increase its speed. Profiling indicates this portion of the program to be relatively slow compared to the rest. Example line (Before Flip): FF FF FF FF 77 AE F0 00 Example line (After Flip): F7 5E EF FF FF FF F0 00

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  • Twitter Search API Question

    - by supermogx
    I'm using the twitter search API to get twitter posts based on some keywords, using AND and OR keyword. It works OK, but I seem to get problems using hashtags... For example : Not returning any results : http://search.twitter.com/search.json?q="%23ipad+AND+%23ipod"+OR+"%23joke+AND+%23funny"&rpp=100&callback=? Returning results : http://search.twitter.com/search.json?q="ipad+AND+ipod"+OR+"joke+AND+funny"&rpp=100&callback=? But there's results with #ipod AND #ipad because when I search only for #ipod, I can see a lot of posts with both hashtags. Example : http://search.twitter.com/search.json?q=%23ipad&rpp=100&callback=? P.S. %23 = # Any idea?

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  • Error using \Glsentrytext{} in section title.

    - by amicitas
    When using the glossaries package in a LaTeX document I occasionally want to use a glossary entry as part of section or chapter title. For example: \section{\Glsentrytext{big}} This however results in an error. Trying to use \protect\Glsentrytext{} does not solve the the problem. Note that using the non-capitalized version (\glsentrytext) does not produce any problems. Does anyone know of a way to get this to work? I use the glossaries package occasionally as way to format specific strings in a consistent way. For example \gls{big} turns into 'beam-into-gas'. Obviously I could create two glossary entries, with and without caps, to achieve this and only include one in the final glossary. That is an ugly solution though.

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  • PgJDBC: "no suitable driver found" when following tutorial, why?

    - by Celeritas
    I'm writing a Java program that queries a PostgreSQL database. I'm following this example and have trouble here: connection = DriverManager.getConnection( "jdbc:postgresql://127.0.0.1:5432/testdb", "mkyong", "123456"); According to the JavaDoc for DriverManager the first string is "a database url of the form jdbc:subprotocol:subname. When I connect to the server I type in psql -h dataserv.abc.company.com -d app -U emp24 and give the password qwe123 (for example sake). What should the first argument of getConnection be? I've tried connection = DriverManager.getConnection( "jdbc:postgresql://dataserv.abc.company.com", "emp24", "qwe123"); and get the run time error: no suitable driver found. I've download JDBC4 Postgresql Driver, Version 9.2-1000.

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  • Retrieving a page of that has a redirect

    - by Dmitry Makovetskiyd
    I get my page content with this function: private function fetch_url($url){ $ch=curl_init($url); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); curl_setopt($ch, CURLOPT_TIMEOUT, 320); $this->doc = curl_exec($ch); $this->status_code= curl_getinfo($ch, CURLINFO_HTTP_CODE); // echo $this->doc; curl_close($ch); } The problem is that with some urls dont exist on a webpage and there is a redirect to another page.. So say if I put the parameter: http://example.com/uncategorized/ It redirect me to : http://example.com/mature/ The problem is with curl, I dont get any content.. But my aim is to get the content of that page redirect.. Is there an easy way to get the function to work in the way I want..?

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  • String loops in Python

    - by Steve Hunter
    I have two pools of strings and I would like to do a loop over both. For example, if I want to put two labeled apples in one plate I'll write: basket1 = ['apple#1', 'apple#2', 'apple#3', 'apple#4'] for fruit1 in basket1: basket2 = ['apple#1', 'apple#2', 'apple#3', 'apple#4'] for fruit2 in basket2: if fruit1 == fruit2: print 'Oops!' else: print "New Plate = %s and %s" % (fruit1, fruit2) However, I don't want order to matter -- for example I am considering apple#1-apple#2 equivalent to apple#2-apple#1. What's the easiest way to code this? I'm thinking about making a counter in the second loop to track the second basket and not starting from the point-zero in the second loop every time.

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  • MySQL - Conflicting WHERE and GROUP BY Statements

    - by TaylorPLM
    I have a query returning the counts of some data, but I do NOT want data that has a null value in it... As an example, the code rolls stats from a clicking system into a table. SELECT sh.dropid, ... FROM subscriberhistory sh INNER JOIN subscriberhistory sh2 on sh.subid = sh2.subid WHERE sh.dropid IS NOT NULL AND sh.dropid != "" ... GROUP BY sh.dropid An example of the record set returned would look like this... 400 2 3 4 5 6 401 2 3 6 5 4 NULL 2 3 4 5 1 There are some other where clauses, and a few more selects (as I said, using the count aggregate) that are also within the query. There is also an order by statement. Again, the goal is to keep the NULL data out of the preceding record set. Could someone explain to me why this behavior is occurring and what to do to solve it.

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  • Handling multiple accounts in Android app

    - by bebeTech
    I would like to build an application that caters for multiple accounts (eg. home, work) and account types (e.g. ISP, VoIP, Mobile). Essentially, I would like to get the user to create the accounts they want and then have all the accounts listed on the start page grouped by type. For example: ISP: - Home - Work Mobile: - Mum - Dad When you click on the account, it would take you to another screen where I do a bunch of calcs and display the results. I currently do this via multiple apps but am looking at consolidating into the one app. I am just not sure where to start or how I go about achieving this? The way the Contacts app works is a good example of what I am wanting to do.

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  • Pyjamas import statements

    - by Gordon Worley
    I'm starting to use Pyjamas and I'm running into some annoyances. I have to import a lot of stuff to make a script work well. For example, to make a button I need to first from pyjamas.ui.Button import Button and then I can use Button. Note that import pyjamas.ui.Button and then using Button.Button doesn't work (results in errors when you build to JavaScript, at least in 0.7pre1). Does anyone have a better example of a good way to do the import statements in Pyjamas than what the Pyjamas folks have on their site? Doing things their way is possible, but ugly and overly complicated from my perspective, especially when you want to use a dozen or more ui components.

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  • ASP.NET web services leak memory when (de)serializing disposable objects?

    - by Serilla
    In the following two cases, if Customer is disposable (implementing IDisposable), I believe it will not be disposed by ASP.NET, potentially being the cause of a memory leak: [WebMethod] public Customer FetchCustomer(int id) { return new Customer(id); } [WebMethod] public void SaveCustomer(Customer value) { // save it } This flaw applies to any IDisposable object. So returning a DataSet from a ASP.NET web service, for example, will also result in a memory leak - the DataSet will not be disposed. In my case, Customer opened a database connection which was cleaned up in Dispose - except Dispose was never called resulting in loads of unclosed database connections. I realise there a whole bunch of bad practices being followed here (its only an example anyway), but the point is that ASP.NET - the (de)serializer - is responsible for disposing these objects, so why doesn't it? This is an issue I was aware of for a while, but never got to the bottom of. I'm hoping somebody can confirm what I have found, and perhaps explain if there is a way of dealing with it.

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