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• How to write a Compiler in C for C

  - by Kerb_z

  I want to write a Compiler for C. This is a Project for my College i am doing as per my University. I am an intermediate programmer in C, with understanding of Data Structures. Now i know a Compiler has the following parts: 1. Lexer 2. Parser 3. Intermediate Code Generator 4. Optimizer 5. Code Generator I want to begin with the Lexer part and move on to Parser. I am consulting the following book: Compilers: Principles, Techniques, and Tools by Alfred V. Aho, Ravi Sethi, Jeffrey D. Ullman. The thing is that this book is highly theoretical and perplexing to me. I really appreciate the authors. But the point is i am not able to begin my project, as if i am blinded where to go. Need guidance please help.

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• help me understand JS execution on onclick event of button

  - by Anil Namde

  <input type="button" name="reset" onclick="return ValidateValue(); __doPostBack('ApplyBtn','')" /> The above is the code generated for asp server button button control on browser. Now my query is that irrespective of ValidateValue() returning true/false __doPostBack('ApplyBtn','') function is not showing any effect for me. My understanding is that string passed to onclick acts like function body, and return will from first function will return control preventing second function from execution. Is that correct ? Please provide helpful inputs.

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• javascript open window references

  - by duckofrubber

  Hi, I'm having some issues understanding how to reference new browser windows after opening them. As an example, if I created 3 new windows from a main one (index.html): var one = window.open( 'one.html', 'one',"top=10,left=10,width=100,height=100,location=no,menubar=no,scrollbars=no,status=no,toolbar=no,resizable=no"); var two = window.open( 'two.html', 'two',"top=100,left=10,width=100,height=100,location=no,menubar=no,scrollbars=no,status=no,toolbar=no,resizable=no"); var three = window.open( 'three.html', 'three',"top=200,left=10,width=100,height=100,location=no,menubar=no,scrollbars=no,status=no,toolbar=no,resizable=no"); two.focus(); How could I programmatically focus on (or just refer to) browser "three" if browser "two" is currently in focus?

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• vestal_versions and htmldiff question of reversion...

  - by holden

  I'm guessing there's probably an easier way to do what I'm doing so that the code is less unwieldy. I had trouble understanding how to use the revert_to method... i wanted something where i could call up two different versions at the same time, but this doesn't seem to be the way that vestal_versions works. This code works, but I'm wondering if I'm making something harder than it needs to be and I'd like to find out before I delve deeper. @article = Article.find(params[:id]) if params[:versions] v = params[:versions].split(',') @article.revert_to(v.first.to_i) @content1 = @article.content @article.revert_to(v.last.to_i) @content2 = @article.content end In case you're wondering, I'm using this in conjunction with HTMLDIFF to get the version changes. <div id="content"> <% if params[:versions] %> <%= Article.diff(@content1, @content2) %> <% else %> <%= @article.content %> <% end %> </div>

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• Theory of computation - Using the pumping lemma for CFLs

  - by Tony

  I'm reviewing my notes for my course on theory of computation and I'm having trouble understanding how to complete a certain proof. Here is the question: A = {0^n 1^m 0^n | n>=1, m>=1} Prove that A is not regular. It's pretty obvious that the pumping lemma has to be used for this. So, we have |vy| = 1 |vxy| <= p (p being the pumping length, = 1) uv^ixy^iz exists in A for all i = 0 Trying to think of the correct string to choose seems a bit iffy for this. I was thinking 0^p 1^q 0^p, but I don't know if I can obscurely make a q, and since there is no bound on u, this could make things unruly.. So, how would one go about this?

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• SqlParameter contructor compiler overload choice

  - by Ash

  When creating a SqlParameter (.NET3.5) or OdbcParameter I often use the SqlParameter(string parameterName, Object value) constructor overload to set the value in one statement. When I tried passing a literal 0 as the value paramter I was initially caught by the C# compiler choosing the (string, OdbcType) overload instead of (string, Object). MSDN actually warns about this gotcha in the remarks section, but the explanation confuses me. Why does the C# compiler decide that a literal 0 parameter should be converted to OdbcType rather than Object? The warning also says to use Convert.ToInt32(0) to force the Object overload to be used. It confusingly says that this converts the 0 to an "Object type". But isn't 0 already an "Object type"? The Types of Literal Values section of this page seems to say literals are always typed and so inherit from System.Object. This behavior doesn't seem very intuitive given my current understanding? Is this something to do with Contra-variance or Co-variance maybe?

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• Xaml not WPF

  - by xan

  I am interested in using Xaml with expression blend for creating user interfaces in an application. However, because of the limitations of the target architecture, I cannot use WPF or C#. So, what I am interested in is in any examples / existing projects or advice from anyone who has experiance of this technology on the use of Xaml in it's "Pure" form as a specification language not tied to WPF. Specific questions: 1) Is it possible to use Blend + Xaml without the WPF elements, or without C# backing classes? 2) Are there any other implementations of Xaml parsers etc. which use different architectures, and can they work with blend or similar tools. 3) Are there alternative editor / designer tools which can help in this situation? I am aware of the MyXaml and MycroXaml projects, and have found a lot of resources on the web about Xaml, but 99% of it relates directly to WPF. This is fine for understanding the concepts of Xaml, but doesn't help with the implimentation I need. Many thanks!

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• how to pass in dynamic data to decorators

  - by steve

  Hi, I am trying to write a base crud controller class that does the following: class BaseCrudController: model = "" field_validation = {} template_dir = "" @expose(self.template_dir) def new(self, *args, **kwargs) .... @validate(self.field_validation, error_handler=new) @expose() def post(self, *args, **kwargs): ... My intent is to have my controllers extend this base class, set the model, field_validation, and template locations, and am ready to go. Unfortunately, decorators (to my understanding), are interpreted when the function is defined. Hence it won't have access to instance's value. Is there a way to pass in dynamic data or values from the sub class? If not, I guess I could use override_template as a workaround to expose and set the template within the controller action. How would I go about validating the form within the controller action? Thanks, Steve

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• Remote Service Vs. Local Service

  - by Nguyen Dai Son

  Dear All, I am a newbiew to Android. I had read a lot of articles about Android Service but I am not clearly understanding what defferent between Local Service and Remote Service (except for "Local Service run in the same process as the lunching activity; remote services run in their own process" - The Busy Coder's Guide to Android Development - Mark L. Murphy ). Please shows me what different between Local Service and Remote Service. What's the advantage/disadvantage of using Local Service. What's the advantage/disadvantage of using Remote Service. Thanks & best regards Dai Son

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• Specification: Use cases for CRUD

  - by Mario Ortegón

  I am writing a Product requirements specification. In this document I must describe the ways that the user can interact with the system in a very high level. Several of these operations are "Create-Read-Update-Delete" on some objects. The question is, when writing use cases for these operations, what is the right way to do so? Can I write only one Use Case called "Manage Object x" and then have these operations as included Use Cases? Or do I have to create one use case per operation, per object? The problem I see with the last approach is that I would be writing quite a few pages that I feel do not really contribute to the understanding of the problem. What is the best practice?

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• nth-child doesn't respond to class

  - by Arne Stephensson

  Is it possible to get the nth-child pseudo-selector to work with a specific class? See this example: http://jsfiddle.net/fZGvH/ I want to have the second DIV.red turn red, but it doesn't apply the color as expected. Not only that, but when you specify this, it changes the 5th DIV to red: div.red:nth-child(6) When you specify this, it changes the 8th DIV to red: div.red:nth-child(9) It seems to be one DIV behind. There are only 8 DIV tags in the example so I don't know why nth-child(9) even works. Testing using Firefox 3.6, but in my actual production code the same problem occurs in Chrome. I'm not understanding something about how this is supposed to work, would appreciate clarification. Also, this will change the 6th DIV to red, but what I actually want is for it to change the second DIV.red to red: div.red:nth-of-type(6) And I don't understand why nth-child() and nth-of-type() respond differently, since there are only eight tags of the same type in the document.

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• php mysql flex unicode

  - by JonoB

  I have a problem with saving the £ symbol to a mysql database. I am running a flex front end, with a php + mysql backend When I save a record from flex, the string gets sent to the server as "This amount is £10" php views the string as above, and when it gets saved into the DB, it gets saved as "This amount is £10". My understanding is that this is correct based on MySQL or PHP is appending a  whenever the £ is used I now retrieve the above record, and it gets sent to flex as "This amount is £10". Flex correctly displays this in a textarea as "This amount is £10" I change another field in the same record in flex, and re-save the transaction. The string now gets sent to the server as "This amount is £10" The record is now saved into the DB as "The amount is £10". Each time the record is re-saved, this effect snowballs. Thanks for any advice you can give.

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• Help me understand Rails eager loading

  - by aaronrussell

  I'm a little confused as to the mechanics of eager loading in active record. Lets say a Book model has many Pages and I fetch a book using this query: @book = Book.find book_id, :include => :pages Now this where I'm confused. My understanding is that @book.pages is already loaded and won't execute another query. But suppose I want to find a specific page, what would I do? @book.pages.find page_id # OR... @book.pages.to_ary.find{|p| p.id == page_id} Am I right in thinking that the first example will execute another query, and therefore making the eager loading pointless, or is active record clever enough to know that it doesn't need to do another query? Also, my second question, is there an argument that in some cases eager loading is more intensive on the database and sometimes multiple small queries will be more efficient that a single large query? Thanks for your thoughts.

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• Are Scala "continuations" just a funky syntax for defining and using Callback Functions?

  - by Alex R

  And I mean that in the same sense that a C/Java for is just a funky syntax for a while loop. I still remember when first learning about the for loop in C, the mental effort that had to go into understanding the execution sequence of the three control expressions relative to the loop statement. Seems to me the same sort of effort has to be applied to understand Continuations (in Scala and I guess probably other languages). And then there's the obvious follow-up question... if so, then what's the point? It seems like a lot of pain (language complexity, programmer errors, unreadable programs, etc) for no gain.

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• browser cookie issue

  - by George2

  Hello everyone, In my previous understanding, for a web site, only login user of a web site (no matter what login/authentication approach is used) could have cookie as persistent identifier, so that if the user close the browser, open browser again to go to the same web site, the web site could remember the user. But I learned recently that it seems for non-login user, there could still be a cookie associated with the user (after the user close browser, and then open the browser again to go to the same web site, the web site could remember the user), and it is called browser cookie? Is that true? If it is true, who is responsible to set the browser cookie? i.e. need some coding/config at web server side, client browser configuration (without coding from server side), or both? How could web server access such cookie? Appreciate if any code samples. thanks in advance, George

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• Best way to save complex Python data structures across program sessions (pickle, json, xml, database

  - by Malcolm

  Looking for advice on the best technique for saving complex Python data structures across program sessions. Here's a list of techniques I've come up with so far: pickle/cpickle json jsonpickle xml database (like SQLite) Pickle is the easiest and fastest technique, but my understanding is that there is no guarantee that pickle output will work across various versions of Python 2.x/3.x or across 32 and 64 bit implementations of Python. Json only works for simple data structures. Jsonpickle seems to correct this AND seems to be written to work across different versions of Python. Serializing to XML or to a database is possible, but represents extra effort since we would have to do the serialization ourselves manually. Thank you, Malcolm

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• JPanel: both implementing my own paintComponent() and rendering children doesn't work

  - by Paul Marshall

  I'm extending a JPanel to display a game board, and adding a JEditorPane at the bottom to hold some status text. Unfortunately, the game board renders just fine, but the JEditorPane is just a blank gray area until I highlight the text in it, when it will render whatever text is highlighted (but not the rest). If I'm understanding Swing right, it should work, because super.paintComponent(g) should render the other children (i.e., the JEditorPane). Tell me, o great stackoverflow, what bonehead mistake am I making? public GameMap extends JPanel { public GameMap() { JEditorPane statusLines = new JEditorPane("text/plain","Stuff"); this.setLayout(new BoxLayout(this,BoxLayout.PAGE_AXIS)); this.add(new Box.Filler(/*enough room to draw my game board*/)); this.add(statusLines); } public void paintComponent(Graphics g){ super.paintComponent(g); for ( all rows ){ for (all columns){ //paint one tile } } } }

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• dynamically populate identy in web.config

  - by user175084

  Is there a way i can dynamically populate the username and password of identity in web.config from my code behind... as i cannot hard code it. <identity impersonate="true" userName = "Admin" password= "xyz"> any help..???? Thanks This the first part the 2nd part i think i can solve if i get this.... 2nd part link text I got a link which might help me solve the problem but i am having difficulty understanding it and implementing..... link text any help...

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• Backup AWS Dynamodb to S3

  - by Ali

  It has been suggested on Amazon docs http://aws.amazon.com/dynamodb/ among other places, that you can backup your dynamodb tables using Elastic Map Reduce, I have a general understanding of how this could work but I couldn't find any guides or tutorials on this, So my question is how can I automate dynamodb backups (using EMR)? So far, I think I need to create a "streaming" job with a map function that reads the data from dynamodb and a reduce that writes it to S3 and I believe these could be written in Python (or java or a few other languages). Any comments, clarifications, code samples, corrections are appreciated.

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• What exactly is a Monad?

  - by WeNeedAnswers

  Can someone please explain to me what a Monad is. I think I grasp Monoids and I grasp that they basically control the input of state into a system. I just look at the text in Haskell and glaze over. A simple example in python would be great. My current understanding is that a Monoid is a procedural piece of code that needs to be read from top to bottom in sequence with the output being the input for the function. I think that I may even got that wrong, but hey I am here to learn.

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• Is there an easy way to convert C# classes to PHP?

  - by John

  I am used to writing C# Windows application. However I have some free hosted PHP web space that I would like to make use of. I have a basic understanding of PHP but have never used it's object oriented capabilities. Is there an easy way to convert C# classes to PHP classes or is it just not possible to write a fully object oriented application in PHP? Update: There are no reliance on the .NET framework beyond the basics. The main aim would be to restructure the class properties, variable enums, etc. The PHP will be hosted on a Linux server.

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• How to reduce java concurrent mode failure and excessive gc

  - by jimx

  In Java, the concurrent mode failure means that the concurrent collector failed to free up enough memory space form tenured and permanent gen and has to give up and let the full stop-the-world gc kicks in. The end result could be very expensive. I understand this concept but never had a good comprehensive understanding of A) what could cause a concurrent mode failure and B) what's the solution?. This sort of unclearness leads me to write/debug code without much of hints in mind and often has to shop around those performance flags from Foo to Bar without particular reasons, just have to try. I'd like to learn from developers here how your experience is. If you had previous encountered such performance issue, what was the cause and how you addressed it? If you have coding recommendations, please don't be too general. Thanks!

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• What is the JavaScript variable scope in a switch / case statment?

  - by Todd Moses

  While creating JavaScript with ASP.NET MVC I noticed several scope warnings and realized that I am missing something with understanding the variable scope inside the switch / case statement. Warning: 'i' is already defined referring to case b and case c My code looks similar to this: switch(element) { case 'a': for(var i=0; i < count; i++){ do something } break; case 'b': for(var i=0; i < count; i++){ do something } break; case 'c': for(var i=0; i < count; i++){ do something } break; } I thought scope ended with each break statement but it seems that scope does not end until the end of the switch/case. Is scope for the entire switch/case?

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• Admin section in CakePHP

  - by Nicklas Ansman

  I'm having a hard time understanding how the CakePHP admin system works. Should all controllers who has an action which requires login include AuthComponent or just the one who handles the login/logout? Let's say I want to protect the add action of a controller. First I create admin_add() in the controller and then in the beforeFilter() method I check if $this->Session->check('Auth.User') is set a redirect based on this? Turns out it was better to just controll this with $this->Auth->allow() What is the easiest way to return to the URL the user was trying to access? Is there a better way than setting a session variable? Turns out it does this automagically :) If someone has a good tutorial for this I would happily read it :) I've already read this tutorial but I found it to be a little to basic and the CakePHP-docs are not that great on this topic either.

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