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• Can I provide nil for the -dequeueReusableCellWithIdentifier: method?

  - by mystify

  dequeueReusableCellWithIdentifier: Returns a reusable table-view cell object located by its identifier. (UITableViewCell *)dequeueReusableCellWithIdentifier:(NSString *)identifier Parameters identifier A string identifying the cell object to be reused. By default, a reusable cell's identifier is its class name, but you can change it to any arbitrary value. Ok so if by default it's the class name, why should I put much brain force into thinking about an identifier? Could I provide just nil? Would it then use the class name? Or what did they try to say here? Must I make an NSString with the class name by myself and provide it as identifier?

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• Quaddratic Bezier Curve: Calculate Tangent

  - by stefan.at.wpf

  Hello, I have have a quadratic bezier curve and I want to calculate the slope of the tangent in a given point. For example, let it be the middlepoint of the quadratic bezier curve, therefore t=0.5 (please see the link below for a picture of this). I've calculated the first derivation of the formula for the quadratic bezier curve, however I get 400 as value for the slope, though it should be 0. Maybe I'm using the first derivation in a wrong way? I know I could also calculate the tangents using trigonometric functions, however I'd like to do it using the first derivation, shouldn't this be possible? Thanks for any hint! For clarification / please note: I'm interested in a general way to get the slope in a arbitrary given point on a quadratic bezier curve, not only to get the tangent in the start- and end point. A picture of my problem including the text above: http://cid-0432ee4cfe9c26a0.skydrive.live.com/self.aspx/%c3%96ffentlich/Quadratic%20Bezier%20Curve.pdf Thank you very much for any hint!

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• Where can I find a description of the old British Standard structured flow charts?

  - by Steve314

  Some professional organisation defined these in, IIRC, the early 80s as similar to the more well known flow charts, but "structured". Instead of having arbitrary "goto" arrows, they had the equivalent of loops etc. They were standardized, and I vaguely remember studying them briefly at O Level. Of course they were about as useful as the well-known chocolate teapot, but I'd still like to be able to find a reference guide for them if possible - for roughly the same reason I was looking for a reference for standard Basic a while back. Google tells me - well, nothing really. They may as well never have existed. Which is probably nearly (and perhaps completely) true - I certainly never heard of them anywhere else except when I was at school. There's a chance that they may even be my computer science teachers little joke.

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• Prevent SQL injection from form-generated SQL - NO PreparedStmts

  - by Markos Fragkakis

  Hi all, I have a search table where user will be able to filter results with a filter of the type: Field [Name], Value [John], Remove Rule Field [Surname], Value [Blake], Remove Rule Field [Has Children], Value [Yes], Remove Rule Add Rule So the user will be able to set an arbitrary set of filters, which will result essentially in a completely dynamic WHERE clause. In the future I will also have to implement more complicated logical expressions, like Where (name=John OR name=Nick) AND (surname=Blake OR surname=Bourne), Of all 10 fields the user may or may not filter by, I don't know how many and which filters the user will set. So, I cannot use a prepared statement (which assumes that at least we know the fields in the WHERE clause). This is why prepared statements are unfortunately out of the question, I have to do it with plain old, generated SQL. What measures can I take to protect the application from SQL Injection (REGEX-wise or any other way)?

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• Generic Data Structure Description Language

  - by Jon Purdy

  I am wondering whether there exists any declarative language for arbitrarily describing the format and semantics of a data structure, that can be compiled to a specific implementation of that structure in any of a set of target languages. That is, something like a generic data definition language but geared toward describing arbitrary data structures such as vectors, lists, trees, etc., and the semantics of operations on those structures. I ask because I had an idea for a feasible implementation of this concept, and I'm just wondering whether it's worth it, and, consequently, whether it's been done before. Another, slightly more abstract question: is there any real difference between the normative specification of a data structure (what it does) and its implementation (how it does it)?

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• Scrape HTML tables from a given URL into CSV

  - by dreeves

  I seek a tool that can be run on the command line like so: tablescrape 'http://someURL.foo.com' [n] If n is not specified and there's more than one HTML table on the page, it should summarize them (header row, total number of rows) in a numbered list. If n is specified or if there's only one table, it should parse the table and spit it to stdout as CSV or TSV. Potential additional features: To be really fancy you could parse a table within a table, but for my purposes -- fetching data from wikipedia pages and the like -- that's overkill. The Perl module HTML::TableExtract can do this and may be good place to start for writing the tool I have in mind. An option to asciify any unicode. An option to apply an arbitrary regex substitution for fixing weirdnesses in the parsed table. Related questions: http://stackoverflow.com/questions/259091/how-can-i-scrape-an-html-table-to-csv http://stackoverflow.com/questions/1403087/how-can-i-convert-an-html-table-to-csv http://stackoverflow.com/questions/2861/options-for-html-scraping

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• Basic Ruby on Rails Question about routing

  - by Acidburn2k

  I have a controller without any related model. This controller is to span some informations from various models. I have lots of actions there, which define certain views on the page. What would be the best way to organize routes for this controller. What I would like is to have /dashboard/something point to any action in the dashboard controller. Not actions like new/edit but arbitrary (showstats, etc). With trail and error I made something like this: map.dashboard 'dashboard/:action', :controller => 'dashboard', :action => :action Now it is possible to access those url using helper: dashboard_url('actionname') This approch seems to be working ok, but is this the way to go? I am not quite sure understand, how are the helper method names generated. How to generate same helper names as in basic controllers "action_controller_url" ? That would be more generic and made the code more consistent. Thanks in advance.

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• Fastest way to calculate an X-bit bitmask?

  - by Virtlink

  I have been trying to solve this problem for a while, but couldn't with just integer arithmetic and bitwise operators. However, I think its possible and it should be fairly easy. What am I missing? The problem: to get an integer value of arbitrary length (this is not relevant to the problem) with it's X least significant bits sets to 1 and the rest to 0. For example, given the number 31, I need to get an integer value which equals 0x7FFFFFFF (31 least significant bits are 1 and the rest zeros). Of course, using a loop OR-ing a shifted 1 to an integer X times will do the job. But that's not the solution I'm looking for. It should be more in the direction of (X << Y - 1), thus using no loops.

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• Using ptrace to generate a stack dump

  - by Gomez

  Hello. I am compiling C++ on *nix and I would like to generate a stack dump a) at an arbitrary point in the program, b) during any signal, particularly during SIGSEGV. Google tells me that ptrace is probably the tool for the job, but I can't find any comprehensible examples of walking the stack. Getting the return address, yeah, but what about the NEXT return address? And what about extracting the symbolic name of the function at that point? Something to do with DWARF? Many thanks if you can tell me where to go from here.

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• calculating the potential effect of inaccurate triangle vertex positions on the triangle edge lenght

  - by stingrey

  i'm not sure how to solve the following problem: i have a triangle with each of the three known vertex positions A,B,C being inaccurate, meaning they can each deviate up to certain known radii rA, rB, rC into arbitrary directions. given such a triangle, i want to calculate how much the difference of two specific edge lengths (for instance the difference between lengths of edge a and edge b) of the triangle may change in the worst case. is there any elegant mathematical solution to this problem? the naive way i thought of is calculating all 360^3 angle combinations and measuring the edge differences for each case, which is a rather high overhead.

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• How to reshape matrices in Mathematica

  - by speciousfool

  When manipulating matrices it is often convenient to change their shape. For instance, to turn an N x M sized matrix into a vector of length N X M. In MATLAB a reshape function exists: RESHAPE(X,M,N) returns the M-by-N matrix whose elements are taken columnwise from X. An error results if X does not have M*N elements. In the case of converting between a matrix and vector I can use the Mathematica function Flatten which takes advantage of Mathematica's nested list representation for matrices. As a quick example, suppose I have a matrix X: With Flatten[X] I can get the vector {1,2,3,...,16}. But what would be far more useful is something akin to applying Matlab's reshape(X,2,8) which would result in the following Matrix: This would allow creation of arbitrary matrices as long as the dimensions equal N*M. As far as I can tell, there isn't anything built in which makes me wonder if someone hasn't coded up a Reshape function of their own.

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• dlopen() with dependencies between libraries

  - by peastman

  My program uses plugins, that are loaded dynamically with dlopen(). The locations of these plugins can be arbitrary, so they aren't necessarily in the library path. In some cases, one plugin needs to depend on another plugin. So if A and B are dynamic libraries, I'll first load A, then load B which uses symbols defined in A. My reading of the dlopen() documentation implies that if I specify RTLD_GLOBAL this should all work. But it doesn't. When I call dlopen() on the second library, it fails with an error saying it couldn't find the first one (which had already been loaded with dlopen()): Error loading library /usr/local/openmm/lib/plugins/libOpenMMRPMDOpenCL.dylib: dlopen(/usr/local/openmm/lib/plugins/libOpenMMRPMDOpenCL.dylib, 9): Library not loaded: libOpenMMOpenCL.dylib Referenced from: /usr/local/openmm/lib/plugins/libOpenMMRPMDOpenCL.dylib Reason: image not found How can I make this work?

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• Any significance to Google's "expires" date being Fri, 01 Jan 1990 00:00:00 GMT?

  - by Robusto

  I was looking at the response headers for my GMail account and noticed that the date Fri, 01 Jan 1990 00:00:00 GMT shows up as the value for "Expires" over and over again. I suppose this is just an easy constant to make sure the browser understands this is past its freshness date. But is there any significance to that particular date? One might as easily have used the same date in 2000, or 1970, or whatever. It's not quirky enough to be someone's birthday or date of college graduation or anything personal like that. Maybe it's just arbitrary, but I was wondering if someone has a good explanation why that particular date was chosen.

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• PHP intersection between array and object

  - by nickf

  I have an object, let's say it's like this: class Foo { var $b, $a, $r; function __construct($B, $A, $R) { $this->b = $B; $this->a = $A; $this->r = $R; } } $f = new Foo(1, 2, 3); I want to get an arbitrary slice of this object's properties as an array. $desiredProperties = array('b', 'r'); $output = magicHere($foo, $desiredProperties); print_r($output); // array( // "b" => 1, // "r" => 3 // )

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• How to determine whether a dependency object implements a given dependency property (C# / WPF)

  - by Tim Coulter

  I am working with the classes in the System.Windows.Documents namespace, trying to write some generic code that will conditionally set the value of certain dependency properties, depending on whether these properties exist on a given class. For example, the following method assigns an arbitrary value to the Padding property of the passed FrameworkContentElement: void SetElementPadding(FrameworkContentElement element) { element.SetValue(Block.PaddingProperty, new Thickness(155d)); } However, not all concrete implementations of FrameworkContentElement have a Padding property (Paragraph does but Span does not) so I would expect the property assignment to succeed for types that implement this property and to be silently ignored for types that do not. But it seems that the above property assignment succeeds for instances of all derivatives of FrameworkContentElement, regardless of whether they implement the Padding property. I make this assumption because I have always been able to read back the assigned value. I assume there is some flaw in the way I am assigning property values. What should I do to ensure that a given dependency property assignment is ignored by classes that do not implement that property? Many thanks for your advice. Tim

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• how to strip namespaces with e4x?

  - by SorcyCat

  I have an arbitrary XML document provided by a URL. I also have an xpath-like expressions. var xml = <doc><node1><node2><node3>some value</node3></node2></node1></doc>; var path = "node1.node2.node3"; I need to verify if the above path into the XML is valid. I tried to do this using eval and E4X. var value = eval("xml."+path); However, my actual xml document has namespaces which are getting in the way. I do not know the namespaces ahead of time or care what they are. Is there a way to strip all the namespaces out ahead of time? Is there a better way to do this? Thanks!

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• java: Preferences API vs. Apache Commons Configuration

  - by Jason S

  I need to allow the user to store/load an arbitrary number of lists of objects (assume they are Serializable). Conceptually I want a data model like class FooBean { /* bean stuff here */ } class FooList { final private Set<FooBean> items = new HashSet<FooBean>(); public boolean add(FooBean item) { return items.add(item); } public boolean remove(FooBean item) { return items.remove(item); } public Collection<FooBean> getItems() { return Collections.unmodifiableSet(items); } } class FooStore { public FooStore() { /* something... uses Preferences or Commons Configuration */ } public FooList load(String key) { /* something... retrieves a FooList associated with the key */ } public void store(String key, FooList items) { /* something... saves a FooList under the given key */ } } Should I use the Preferences API or Commons Config? What's the advantages of each?

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• Non-reentrant C# timer

  - by Oak

  I'm trying to invoke a method f() every t time, but if the previous invocation of f() has not finished yet, wait until it's finished. I've read a bit about the available timers (this is a useful link) but couldn't find any good way of doing what I want, save for manually writing it all. Any help about how to achieve this will be appreciated, though I fear I might not be able to find a simple solution using timers. To clarify, if x is one second, and f() runs the arbitrary durations I've written below, then: Step Operation Time taken 1 wait 1s 2 f() 0.6s 3 wait 0.4s (because f already took 0.6 seconds) 4 f() 10s 5 wait 0s (we're late) 6 f() 0.3s 7 wait 0.7s (we can disregard the debt from step 4) Notice that the nature of this timer is that f() will not need to be safe regarding re-entrance, and a thread pool of size 1 is enough here.

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• How to show an animated spinner while a background task is processing in nested rails model using aj

  - by Globalkeith

  My specific example is highly complex, so I will use the example shown by Ryan from Railscasts to discuss this: http://railscasts.com/episodes/197-nested-model-form-part-2 Background I have a form, let's say "Survey", which contains an arbitrary number of "Questions". Senario Give i am on the "Edit Survey" page. I would like to add a button to each "Question" field which calls a remote_function, which in turn queue's up a delayed_job to execute some processing on the "Question". To give feedback to the user, i would like to disable the button, and show an animated spinner, which remains until the delayed_job has processed the "Question". Hint - I can add methods to the "Question" model to indicate the status of the delayed_job. So, with best practices in mind, what is the best way to achieve this?

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• How to pass a string containing both single and double quotes as a parameter to XSLT in PHP?

  - by Boaz

  Hi, I have a simple PHP-based XSLT trasform code that looks like that: $xsl = new XSLTProcessor(); $xsl->registerPHPFunctions(); $xsl->setParameter("","searchterms", $searchterms); $xsl->importStylesheet($xslDoc); echo $xsl->transformToXML($doc); The code passes the variable $searchterms, which contains a string, as a parameter to the XSLT style sheet which in turns uses it as a text: <title>search feed for <xsl:value-of select="$searchterms"/></title> This works fine until you try to pass a string with mixes in it, say: $searchterms = '"some"'." text's quotes are mixed." In that point the XSLT processor screams: Cannot create XPath expression (string contains both quote and double-quotes) What is the correct way to safely pass arbitrary strings as input to XSLT? Note that these strings will be used as a text value in the resulting XML and not as an XPATH paramater. Thanks, Boaz

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• basic sql group by with percentage

  - by David in Dakota

  I have an issue and NO it is not homework, it's just a programmer who has been away from SQL for a long time having to solve a problem. I have the following table: create table students( studentid int identity(1,1), [name] varchar(200), [group] varchar(10), grade numeric(9,2) ) go The group is something arbitrary, assume it's the following "Group A", "Group B"... and so on. The grade is on a scale of 0 - 100. If there are 5 students in each group with grades randomly assigned, what is the best approach to getting the top 3 students (the top 80%) based on their grade? To be more concrete if I had the following: Ronald, Group A, 84.5 George H, Group A, 82.3 Bill, Group A, 92.0 George W, Group A, 45.5 Barack, Group A, 85.0 I'd get back Ronald, Bill, and Barack. I'd also need to do this over other groups.

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• Programmatic use of ARP

  - by sizzzzlerz

  I have a need for some C or C++ code, compilable under Linux, to be able to take a list of IP addresses of some arbitrary number of remote hosts machines and obtain a ethernet MAC address for each one. These host machines may be on the same subnet or they could be on a different subnet behind a router. Its OK if the MAC address of some or all of the remote hosts is the address of the interface on the router. Ultimately, I want to hand off the IP address and MAC address to an FPGA who will use these pieces of information to format and send UDP/IP packets over ethernet to the hosts. Obviously, the FPGA will also be given its own MAC address and IP address to fill in the source MAC and source IP addresses in the packets. Is there some code I can be pointed to that can create and broadcast ARP packets to these remote machines and receive back the ARP response packets such that the destination MAC addresses can be extracted?

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• How does Linq-to-Xml convert objects to strings?

  - by Eamon Nerbonne

  Linq-to-Xml contains lots of methods that allow you to add arbitrary objects to an xml tree. These objects are converted to strings by some means, but I can't seem to find the specification of how this occurs. The conversion I'm referring to is mentioned (but not specified) in MSDN. I happen to need this for javascript interop, but that doesn't much matter to the question. Linq to Xml isn't just calling .ToString(). Firstly, it'll accept null elements, and secondly, it's doing things no .ToString() implementation does: For example: new XElement("elem",true).ToString() == "<elem>true</elem>" //but... true.ToString() == "True" //IIRC, this is culture invariant, but in any case... true.ToString(CultureInfo.InvariantCulture) == "True" Other basic data types are similarly specially treated. So, does anybody know what it's doing and where that's described?

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• Strange crashes on the iPad device with core graphics functions

  - by toastie

  I am getting a lot of strange EXC_BAD_ACCESS crashes on the iPad that only happen on the device and not in the simulator. I am assuming that they are somehow memory related, but I am not sure. They all happen with image context related functions. One strange example is using CGImageCreateWithImageInRect. For example, if i run through a bunch of UIImages and crop them with CGImageCreateWithImageInRect, it will always crash at specific arbitrary sizes. Like, if I crop them all to 200x200, it crashes out after processing 12 images. If i crop them to 210x210, it works no problem. The EXC_BAD_ACCESS happens inside of "memmove" called from "CGBlt_copyBytes". That is all the debugger shows me strangely enough. I can't see the callstack going up to any of my methods. All of this works fine in the simulator! I know this is all very vague, but if anyone has any ideas, they would be greatly appreciated.

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• How to get a clipboard paste notification and provide my own data?

  - by Uwe Keim

  For a small utility I am writing (.NET, C#), I want to monitor clipboard copy operations and clipboard paste operations. My idea is to provide my own data when pasting into an arbitrary application. The monitoring of a copy operation can be easily done by using a clipboard viewer. Something that seems much more advanced to me is to write a "clipboard paste provider": Answer to "what formats are available" queries of applications. Supply data to application paste operations. I found this posting and this posting, but none of them seems to really help me. What I guess is that I somehow have to mimic/hijack the current clipboard. Question: Is it possible to "wrap" the clipboard in terms of paste operations and provide my own kind of "clipboard proxy"? Thanks Uwe

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