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• Is there really such a thing as "being good at math"?

  - by thezhaba

  Aside from gifted individuals able to perform complex calculations in their head, I'm wondering if proficiency in mathematics, namely calculus and algebra, has really got to do with one's natural inclination towards sciences, if you can put it that way. A number of students in my calculus course pick up material in seemingly no time whereas I, personally, have to spend time thinking about and understanding most concepts. Even then, if a question that requires a bit more 'imagination' comes up I don't always recognize the concepts behind it, as is the case with calculus proofs, for instance. Nevertheless, I refuse to believe that I'm simply not made for it. I do very well in programming and software engineering courses where a lot of students struggle. At first I could not grasp what they found to be so difficult, but eventually I realized that having previous programming experience is a great asset -- once I've seen and made practical use of the programming concepts learning about them in depth in an academic setting became much easier as I have then already seen their use "in the wild". I suppose I'm hoping that something similar happens with mathematics -- perhaps once the practical idea behind a concept (which authors of textbooks sure do a great job of concealing..) is evident, understanding the seemingly dry and symbolic ideas and proofs would be more obvious? I'm really not sure. All I'm sure of is I'd like to get better at calculus, but I don't yet understand why some of us pick it up easily while others have to spend considerable amounts of time on it and still not have complete understanding if an unusual problem is given.

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• Visual Studio 2012 won't start

  - by David Aleu

  I installed VS2012 Premium from our MSDN subscription and it was working fine the first couple of days but then I installed a few extensions I can't now start VS2012 and it gives the error: Faulting application name: devenv.exe, version: 11.0.50727.1, time stamp: 0x5011ecaa Faulting module name: ntdll.dll, version: 6.1.7601.17725, time stamp: 0x4ec49b8f Exception code: 0xc0000374 Fault offset: 0x000ce6c3 Faulting process id: 0xee8 Faulting application start time: 0x01cd89bb777fc1dd Faulting application path: C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\devenv.exe Faulting module path: C:\Windows\SysWOW64\ntdll.dll I'm running it on Windows 7 64 bit. I've tried to repair, uninstall and install again and nothing. I tried to restore to a previous restore system point but nothing. The extensions I installed I can remember: VS10x Code Map VSCommands Visual SVN Nuget manager (all the above my colleagues have it too and it works fine for them) and: Web Essentials Visual Studio Color Theme Editor SlowCheetah Mobile Ready HTML5 Questions are: Anyone else has had this problem? Is there a way I can uninstall extensions from a command line or software? (I removed the extensions folder but that doesn't do anything) Can I repair the "C:\Windows\SysWOW64\ntdll.dll"? Is it really a problem with this dll? I haven't been able to find any similar issue in other versions and because VS2012 is new doesn't seem to be much information either.

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• Undesired Output of Crontab Job Using CURL

  - by Russell C.

  I have written a perl script that runs as a daily crontab job that uploads files to Amazon S3 via CURL. I want the output of the cron job emailed to me which works fine but I don't want that email to include messages related to the CURL upload (only those message my script is outputting). Here are the CURL related messages I'm seeing in the daily email right now: % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 230M 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 0 230M 0 0 0 544k 0 1519k 0:02:35 --:--:-- 0:02:35 1807k 0 230M 0 0 0 1744k 0 1286k 0:03:03 0:00:01 0:03:02 1342k 1 230M 0 0 1 2880k 0 1219k 0:03:13 0:00:02 0:03:11 1250k 1 230M 0 0 1 4016k 0 1198k 0:03:17 0:00:03 0:03:14 1218k 2 230M 0 0 2 5168k 0 1186k 0:03:19 0:00:04 0:03:15 1202k 2 230M 0 0 2 6336k 0 1181k 0:03:19 0:00:05 0:03:14 1157k 3 230M 0 0 3 7488k 0 1177k 0:03:20 0:00:06 0:03:14 1147k 3 230M 0 0 3 8592k 0 1167k 0:03:22 0:00:07 0:03:15 1142k 4 230M 0 0 4 9744k 0 1166k 0:03:22 0:00:08 0:03:14 1145k 4 230M 0 0 4 10.6M 0 1163k 0:03:23 0:00:09 0:03:14 1142k 5 230M 0 0 5 11.7M 0 1161k 0:03:23 0:00:10 0:03:13 1140k 5 230M 0 0 5 12.8M 0 1158k 0:03:23 0:00:11 0:03:12 1133k 6 230M 0 0 6 13.9M 0 1155k 0:03:24 0:00:12 0:03:12 1138k 6 230M 0 0 6 15.0M 0 1155k 0:03:24 0:00:13 0:03:11 1138k 7 230M 0 0 7 16.1M 0 1152k 0:03:25 0:00:14 0:03:11 1131k 7 230M 0 0 7 17.2M 0 1152k 0:03:25 0:00:15 0:03:10 1132k 7 230M 0 0 7 18.4M 0 1152k 0:03:24 0:00:16 0:03:08 1140k I am using a simple Perl system() call to invoke CURL. Does anyone know what command line argument I can supply CURL to turn off the reporting of the upload progress? Thanks in advance for your help!

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• [C#] how to do Exception Handling & Tracing

  - by shrimpy

  Hi all, i am reading some C# books, and got some exercise don't know how to do, or not sure what does the question mean. Problem: After working for a company for some time, your skills as a knowledgeable developer are recognized, and you are given the task of “policing” the implementation of exception handling and tracing in the source code (C#) for an enterprise application that is under constant incremental development. The two goals set by the product architect are: 100% of methods in the entire application must have at least a standard exception handler, using try/catch/finally blocks; more complex methods must also have additional exception handling for specific exceptions All control flow code can optionally write “tracing” information to assist in debugging and instrumentation of the application at run-time in situations where traditional debuggers are not available (eg. on staging and production servers). (i am not quite understand these criterias, i came from the java world, java has two kind of exception, check and unchecked exception. Developer must handle checked exception, and do logging. about unchecked exception, still do logging maybe, but most of the time we just throw it. however here comes to C#, what should i do????) Question for Problem: List rules you would create for the development team to follow, and the ways in which you would enforce rules, to achieve these goals. How would you go about ensuring that all existing code complies with the rules specified by the product architect; in particular, what considerations would impact your planning for the work to ensure all existing code complies?

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• Is there a way to detect Layout or Display changes in WPF?

  Hello! I am trying to check how fast the Frame control can display a FixedPage object when it is assigned to Frame.Content property. I plan to check the tick count before and after the assignment to the Content property. Example: int starttime = Environment.TickCount; frame1.Content = fixedpage; int endtime = Environment.TickCount; The problem is that the assignment to the Content property might be asynchronous and returns immediately therefore i get a zero amount of time. The rendering of the FixedPage however visually has a lag time from assignment of the Content property up to the point where the FixedPage appears on screen. The Frame.ContentChanged() event is no good either because it gets triggered even before the FixedPage appears on screen so it's not accurate. I'm thinking of detecting the change on the window or control's display instead in order to get the time when the FixedPage is actually displayed on screen. Is there a way to do this in WPF? Thanks!

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• Tips for submitting a library to Boost?

  - by AraK

  Hi everyone, Summer is coming, and a group of friends and I are getting ready for it :) We decided to build a compile-time Arbitrary precision Unsigned Integers. We would like to provide a set of integers algorithms(functions) with the library. We have seen a number of requests for such a library(SoC2010, C++0x Standard Library wishlist). Also, a regular run-time bigint is requested usually with that, but we don't want to go into the hassle of memory management. The idea came to me from a library called TTMath, unfortunately this library works only on specific platforms because Assembly was used extensively in the library. We would like to write a standard library, depending on the C++ standard library and Boost. Also, we would like to use the available C++0x facilities in current compilers like user-defined literals and others. This would technically make the library non-standard for a while, but we think that it is a matter of time the new standards will be official. Your hints on the whole process including design, implementation, documentation, maintainable of the library are more than welcom. We are a group of students and fresh graduates who are looking for something interesting in the summer, but we see that Boost is full of gurus and we don't want to forget something too obvious. We are communicating on-line, so there is no shared white-boards :( Thanks,

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• Arduino variable going blank after first pass.

  - by user541597

  I have an arduino sketch that takes a timet and when that timet is equal to the current time it sets the new timet to timet + 2. For example: char* convert(char* x, String y){ int hour; int minute; sscanf(x, "%d:%d", &hour, &minute); char buf[6]; if (y == "6"){ if (hour > 17){ hour = (hour+6)%24; snprintf(buf, 10, "%d:%d", hour, minute ); }else if (hour < 18){ //hour = hour + 6; minute = (minute + 2); snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "12"){ if (hour > 11){ hour = (hour+12)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } else if (hour < 12){ hour = hour + 12; snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "24"){ hour = (hour+24)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } return buf; } sketch starts for example at 1:00am timet is set to 1:02, at system time 1:02 timet == system time my loops looks like this: if (timet == currenttime){ timet = convert(timet) } From this now when ever I check the value of timet it should equal 1:04, however I am getting the correct value at the first run after the execution of convert however everytime after that my timet value is blank. I tried changing the code instead of using the if loop I only run the convert function when I send for example t through the serial monitor, this works fine and outputs the correct timet after the execution of the convert function, So I figured the problem is in the if loop... Any ideas?

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• JSP getParameter problem

  - by user236501

  I have a form, if the timer reach the form will auto redirect to the Servlet to update database. My problem now is if javascript redirect the window to servlet my request.getParameter is null. function verify(f,whichCase){ if(whichCase == "Submit"){ msg = "Are you sure that you want to submit this test?"; var i = confirm(msg) if(i){ parent.window.location = "sindex.jsp" } return i; } } I doing this because i got a iframe in my jsp. Timer update problem have to use iframe. So, when time up or user click submit parent.window.location can let me refresh parent window <form method="POST" action="${pageContext.request.contextPath}/TestServlet" onSubmit="return verify(this,whichPressed)"> My form when user click submit button within the timing, it will trigger the verify function to let user confirm submit. So inside my TestServlet i got this, because using javascript redirect request.getParameter("answer") this keep return me null. protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if (request.getParameter("Submit") != null) { String ans = request.getParameter("answer"); Answer a = new Answer(ans, no); aa.CreateAnswer(an,t.getTestCode(),username); RequestDispatcher rd = request.getRequestDispatcher("/sindex.jsp"); rd.forward(request, response); } } Below are my timer when time up redirect to TestServlet trigger the doGet method if((mins == 0) && (secs == 0)) { window.alert("Time is up. Press OK to submit the test."); // change timeout message as required var sUrl = "TestServlet"; parent.window.location = sUrl // redirects to specified page once timer ends and ok button is pressed } else { cd = setTimeout("redo()",1000); }

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• What happens when modifying Gemfile.lock directly?

  - by Mik378

  Since the second time of bundle install execution, dependencies are loaded from Gemfile.lock when Gemfile isn't changed. But I wonder how detection of changes is made between those two files. For instance, if I'm adding a new dependency directly into Gemfile.lock without adding it into Gemfile (as opposed to the best practice since Gemfile.lock is auto-generated from Gemfile), would a bundle install consider Gemfile as changed ? Indeed, does bundle install process compares the whole Gemfile and Gemfile.lock trees in order to detect changes? If it is, even if I'm adding a dependency directly to Gemfile.lock, Gemfile would be detected as changed (since different) and would re-erase Gemfile.lock (so losing the added dependency...) What is the process of bundle install since the launch for the second time ? To be more clear, my question is: Are changes based only from Gemfile ? That means bundler would keep a Gemfile snapshot of every bundle install execution number N and merely compares it to the bundle install execution N+1 ? Or none snapshot are created in bundler memory and bundler makes a comparison with Gemfile.lock each time to detect if Gemfile must be considered as changed.

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• Create unique identifier for different row-groups

  - by Max van der Heijden

  I want to number certain combinations of row in a dataframe (which is ordered on ID and on Time) tc <- textConnection(' id time end_yn number abc 10 0 1 abc 11 0 2 abc 12 1 3 abc 13 0 1 def 10 0 1 def 15 1 2 def 16 0 1 def 17 0 2 def 18 1 3 ') test <- read.table(tc, header=TRUE) The goal is to create a new column ("journey_nr") that give a unique number to each row based on the journey it belongs to. Journeys are defined as a sequence of rows per id up until to end_yn == 1, also if end_ynnever becomes 1, the journey should also be numbered (see the expected outcome example). It is only possible to have end_yn == 0 journeys at the end of a collection of rows for an ID (as shown at row 4 for id 3). So either no end_yn == 1 has occured for that ID or that happened before the end_yn == 0-journey (see id == abc in the example). I know how to number using the data.table package, but I do not know which columns to combine in order to get the expected outcome. I've searched the data.table-tag on SO, but could not find a similar problem. Expected outcome: id time end_yn number journey abc 10 0 1 1 abc 11 0 2 1 abc 12 1 3 1 abc 13 0 1 2 def 10 0 1 3 def 15 1 2 3 def 16 0 1 4 def 17 0 2 4 def 18 1 3 4

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• Type of member is not CLS-compliant

  - by John Galt

  Using Visual Studio 2008 and VB.Net: I have a working web app that uses an ASMX web service which is compiled into its separate assembly. I have another class library project compiled as a separate assembly that serves as a proxy to this web service. This all seems to work at runtime but I am getting this warning at compile time which I don't understand and would like to fix: Type of member 'wsZipeee' is not CLS-compliant I have dozens of webforms in the main project that reference the proxy class with no compile time complaints as this snippet shows: Imports System.Data Partial Class frmZipeee Inherits System.Web.UI.Page Public wsZipeee As New ProxyZipeeeService.WSZipeee.Zipeee Dim dsStandardMsg As DataSet Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load And yet I have one webform (also in the root of the main project) which gives me the "not CLS-compliant" message but yet attempts to reference the proxy class just like the other ASPX files. I get the compile time warning on the line annoted by me with 'ERROR here.. Imports System.Data Partial Class frmHome Inherits System.Web.UI.Page Public wsZipeee As New ProxyZipeeeService.WSZipeee.Zipeee ERROR here Dim dsStandardMsg As DataSet Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load This makes no sense to me. The file with the warning is called frmHome.aspx.vb; all others in the project declare things the same way and have no warning. BTW, the webservice itself returns standard datatypes: integer, string, and dataset.

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• How to get timestamp of tick precision in .NET / C#?

  - by Hermann

  Up until now I used DateTime.Now for getting timestamps, but I noticed that if you print DateTime.Now in a loop you will see that it increments in descrete jumps of approx. 15 ms. But for certain scenarios in my application I need to get the most accurate timestamp possible, preferably with tick (=100 ns) precision. Any ideas? Update: Apparently, StopWatch / QueryPerformanceCounter is the way to go, but it can only be used to measure time, so I was thinking about calling DateTime.Now when the application starts up and then just have StopWatch run and then just add the elapsed time from StopWatch to the initial value returned from DateTime.Now. At least that should give me accurate relative timestamps, right? What do you think about that (hack)? NOTE: StopWatch.ElapsedTicks is different from StopWatch.Elapsed.Ticks! I used the former assuming 1 tick = 100 ns, but in this case 1 tick = 1 / StopWatch.Frequency. So to get ticks equivalent to DateTime use StopWatch.Elapsed.Ticks. I just learned this the hard way. NOTE 2: Using the StopWatch approach, I noticed it gets out of sync with the real time. After about 10 hours, it was ahead by 5 seconds. So I guess one would have to resync it every X or so where X could be 1 hour, 30 min, 15 min, etc. I am not sure what the optimal timespan for resyncing would be since every resync will change the offset which can be up to 20 ms.

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• What hash algorithms are parallelizable? Optimizing the hashing of large files utilizing on multi-co

  - by DanO

  I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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• Java reflection appropriateness

  - by jsn

  This may be a fairly subjective question, but maybe not. My application contains a bunch of forms that are displayed to the user at different times. Each form is a class of its own. Typically the user clicks a button, which launches a new form. I have a convenience function that builds these buttons, you call it like this: buildButton( "button text", new SelectionAdapter() { @Override public void widgetSelected( SelectionEvent e ) { showForm( new TasksForm( args... ) ); } } ); I do this dozens of times, and it's really cumbersome having to make a SelectionAdapter every time. Really all I need for the button to know is what class to instantiate when it's clicked and what arguments to give the constructor, so I built a function that I call like this instead: buildButton( "button text", TasksForm.class, args... ); Where args is an arbitrary list of objects that you could use to instantiate TasksForm normally. It uses reflection to get a constructor from the class, match the argument list, and build an instance when it needs to. Most of the time I don't have to pass any arguments to the constructor at all. The downside is obviously that if I'm passing a bad set of arguments, it can't detect that at compilation time, so if it fails, a dialog is displayed at runtime. But it won't normally fail, and it'll be easy to debug if it does. I think this is much cleaner because I come from languages where the use of function and class literals is pretty common. But if you're a normal Java programmer, would seeing this freak you out, or would you appreciate not having to scan a zillion SelectionAdapters?

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• Accessing an Access DB from Outlook via VBA

  - by camastanta

  Hi The situation: In Outlook I get a message from a server. The content of the message needs to be put into an Access db. But, there may not exist another message with the same date. So, I need to look into a db if there is already a message with the same date and time. If there exists one, then it needs to be replaced and otherwise the message needs to be added to the database. The database contains a list of current positions from the vehicles on the road. The problem: I have problems to compare a date time with a date time in an Access DB via VBA. The query I use returns no records but there is a record in the database. This is the query I use: adoRS.Open "SELECT * FROM currentpositions WHERE ((currentpositions. [dateLT])=" & "#" & date_from_message & "#" & ")", adoConn, adOpenStatic, adLockOptimistic Second I need to now what the result is of that query. How can I determine the number of records that my query gives me? Thanks camastanta

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• unbuffered I/O in Linux

  - by stuck

  I'm writing lots and lots of data that will not be read again for weeks - as my program runs the amount of free memory on the machine (displayed with 'free' or 'top') drops very quickly, the amount of memory my app uses does not increase - neither does the amount of memory used by other processes. This leads me to believe the memory is being consumed by the filesystems cache - since I do not intend to read this data for a long time I'm hoping to bypass the systems buffers, such that my data is written directly to disk. I dont have dreams of improving perf or being a super ninja, my hope is to give a hint to the filesystem that I'm not going to be coming back for this memory any time soon, so dont spend time optimizing for those cases. On Windows I've faced similar problems and fixed the problem using FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH - the machines memory was not consumed by my app and the machine was more usable in general. I'm hoping to duplicate the improvements I've seen but on Linux. On Windows there is the restriction of writing in sector sized pieces, I'm happy with this restriction for the amount of gain I've measured. is there a similar way to do this in Linux?

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• When is Googling it wrong?

  - by Drahcir

  I've been going through Stack Overflow for quite a bit now and noticed certain people (usually experienced programmers) frown upon Googling (researching) certain problems. Since I myself tend to use Google quite a bit to solve certain programming related issues I found certain comments rather demoralising. Now some of you may have come here trigger happy to delete this post but I needed some clarification. I usually Google things that usually syntax related that I would have never figured out on my own. For example I once wondered how to access the properties of a class that I didn't have a direct relationship to. So after a bit of research I discovered reflection and got what I wanted. Now in another scenario is learning a new language, in my case Silverlight were it differs in certain aspects of .NET compared to say ASP.NET. A few weeks ago I had no idea how to load another Silverlight page (usercontrol) and had to Google my way to the solution which I found wasn't as simple as I had imagined. In scenario three is were I myself frown up, that is just stealing a huge chunk of code to avoid doing the work yourself, for example paging a HTML table using JavaScript, where one just copies and pastes the JavasSript code without as much as trying to understand how it works. I do admit I have done this once or twice before for trivial tasks that had very little time limit and weren't all that important but most of the time still have to throw away what I found because it took too much time to adapt it and get what I wanted out of it. In the last scenario, I sometimes have a piece of code that I would be really unhappy about, as in I find it sloppy or too overcomplicated and try to look on the Internet to see other ways to tackle the same problem, let's say filtering through a table. With the knowledge I acquire I learned new coding practices that help me work more efficiently like "Do not repeat yourself" and such. Now in your opinion when do you find it wrong to use Google (or any other researching tool) to find a solution to your problem?

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• Why does Eclipse skip lines when I debug JBoss?

  - by ZeKoU

  Hi, I am trying to debug web service call which uses JMS in the background.I have JBoss running in debug mode. What happens is that when I press F6 in Eclipse (to execute current line) it skips certain lines. I have this method: @Override public void log(MsgPayload payload) { 1 Date startTime = new Date(); logger.info("Publishing with BufferedPublisher.java start time:"+startTime); 3 publisher.send(payload); Date endTime = new Date(); logger.info("Publishing with BufferedPublisher.java end time:"+endTime); long mills = endTime.getTime()-endTime.getTime(); double secs = mills/1000.0; logger.info("Publishing with BufferedPublisher.java total time (seconds):"+secs); } So what happens? I have breakpoint at line 1. When I press F6 it skips that line and goes to line 3. When I press F6 again it goes to the end of the method. Half of the code is never executed..??? My question is why. I am assuming my source is not well attached to the real code that is being executed.But how do I change this? Thanks.

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• Best way to carry & modify a variable through various instances and functions?

  - by bobsoap

  I'm looking for the "best practice" way to achieve a message / notification system. I'm using an OOP-based approach for the script and would like to do something along the lines of this: if(!$something) $messages->add('Something doesn\'t exist!'); The add() method in the messages class looks somewhat like this: class messages { public function add($new) { $messages = $THIS_IS_WHAT_IM_LOOKING_FOR; //array $messages[] = $new; $THIS_IS_WHAT_IM_LOOKING_FOR = $messages; } } In the end, there is a method in which reads out $messages and returns every message as nicely formatted HTML. So the questions is - what type of variable should I be using for $THIS_IS_WHAT_IM_LOOKING_FOR? I don't want to make this use the database. Querying the db every time just for some messages that occur at runtime and disappear after 5 seconds just seems like overkill. Using global constants for this is apparently worst practice, since constants are not meant to be variables that change over time. I don't even know if it would work. I don't want to always pass in and return the existing $messages array through the method every time I want to add a new message. I even tried using a session var for this, but that is obviously not suited for this purpose at all (it will always be 1 pageload too late). Any suggestions? Thanks!

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• Inheritence and usage of dynamic_cast

  - by Mewzer

  Hello, Suppose I have 3 classes as follows (as this is an example, it will not compile!): class Base { public: Base(){} virtual ~Base(){} virtual void DoSomething() = 0; virtual void DoSomethingElse() = 0; }; class Derived1 { public: Derived1(){} virtual ~Derived1(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD1DoSomething{ ... } }; class Derived2 { public: Derived2(){} virtual ~Derived2(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD2DoSomething{ ... } }; I want to create an instance of Derived1 or Derived2 depending on some setting that is not available until run-time. As I cannot determine the derived type until run-time, then do you think the following is bad practice?... class X { public: .... void GetConfigurationValue() { .... // Get configuration setting, I need a "Derived1" b = new Derived1(); // Now I want to call the special DoSomething for Derived1 (dynamic_cast<Derived1*>(b))->SpecialD1DoSomething(); } private: Base* b; }; I have generally read that usage of dynamic_cast is bad, but as I said, I don't know which type to create until run-time. Please help!

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• How did you learn to be a programming guru?

  - by Xonara

  College courses are obviously very helpful, but I hear all the time about great programmers that just "taught themselves," and I wonder how the hell they did it. Online tutorials are nice - online support, even better - but learning with nothing but online resources is difficult to say the least, and I don't know anybody that's experienced enough to help me learn. Even if I did, they probably wouldn't have the time for it. Any advice is greatly appreciated. Becoming an application/game designer is something I've wanted to achieve for a long, long time, even if I never use it for a career, and it does mean alot to me. However, I'm constantly thwarted by lack of motivation, or perhaps confidence. Though I've found some good tutorials online, sometimes I feel it just isn't enough to really get me somewhere, and my limited knowledge of computers (and any other technology) in general is hardly reassuring. I'm constantly getting the feeling that maybe it isn't "in me." Well, guess that's it. I just don't want to join the legions of aspiring techies that just gave up.

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• How to end a thread in perl

  - by user1672190

  I am new to perl and i have a question about perl thread. I am trying to create a new thread to check if the running function is timed out, and my way of doing it is as below. Logic is 1.create a new thread 2.run the main function and see if it is timed out, if ture, kill it Sample code: $exit_tread = false; # a flag to make sure timeout thread will run my $thr_timeout = threads->new( \&timeout ); execute main function here; $exit_thread = true # set the flag to true to force thread ends $thr_timeout->join(); #wait for the timeout thread ends Code of timeout function sub timeout { $timeout = false; my $start_time = time(); while (!$exit_thread) { sleep(1); last if (main function is executed); if (time() - $start_time >= configured time ) { logmsg "process is killed as request timed out"; _kill_remote_process(); $timeout = true; last; } } } now the code is running as i expected, but i am just not very clear if the code $exit_thread = true works because there is a "last" at the end of while loop. Can anybody give me a answer? Thanks

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• Get information from WebPage.

  - by william-hu

  I want to set up an app which can get the information from a particular web page. Then i display the value which got from that page to the iPhone user. Detail:In the webpage on server ,there is the schedule for bus time. If the user input origin and terminus then show the user the time information(list on webpage) in a label. That's all. What i have finished is : Open the iphone app, input two value(origin and terminus) to UITextField. Send the URL to server. Get the page, and show in UIWebView. What my problem next is how should i get the information form that page into another two labels to give the user about the bus time. I have store data in my Array receiveData: self.receivedData = data; I am not clear the data i received is XML or what? And how should i pick-up the value i want. (should i save the value to property list and the read the value?) Thank you so much!

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• I need some ideas on my algortihm for a Hit Counter

  - by stckvrflw

  My algorithm is for a hit count, I am tring to not count for the same person twice if that person came to the site twice in a time internval (For example if he comes twice in 5 minutes, I want to count it as 1 for this person) Here how my database looks like UserIp UserId Date of user came 127.0.0.1 new.user.akb 26.03.2010 10:15:44 127.0.0.1 new.user.akb 26.03.2010 10:16:44 127.0.0.1 new.user.akb 26.03.2010 10:17:44 127.0.0.1 new.user.akb 26.03.2010 10:18:44 127.0.0.1 new.user.akb 26.03.2010 10:19:44 127.0.0.1 new.user.akb 26.03.2010 10:20:44 127.0.0.1 new.user.akb 26.03.2010 10:21:44 127.0.0.1 new.user.akb 26.03.2010 10:22:44 127.0.0.1 new.user.akb 26.03.2010 10:23:44 What I need to do is get number of distinct UserIPs from the table above that occured within a time interval. For example if I set the time interval for 5 minutes, and let say that is starts at 26.03.2010 10:15:44 Then I will get 2 as the results, since 1 distinct value between 10:15 to 10:20 and , 1 distinct value from 10:20 to 10:23, For example if my interval is 3 minutes than the return result will be 3 Thanks.

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• What's the best approach for getting into VS2010, C# 4, and WPF if my background is in C++/MFC

  - by Canacourse

  All my past programming experience has been in C++ on VS2003/8, Mostly service based and completely self taught. 2 Years ago I had to create my first real GUI app and (Foolishly) choose MFC. I got the app working but it took a long time & was a bit of a nightmare to learn MCF (and its many shortcomings) but I ended up with a reliable workable app which was difficult to change or extend. Again I have to create another GUI app more complex than the first and again this will be created from scratch and will only ever be used on windows. I had put off learning C# for a long time but not wishing to re-visit MFC have decided that the new application with be birthed in VS2010 and WPF 4 will be the midwife. Trying to avoid the several expensive (Time wise) mistakes I made previously. Im looking for for good books/tutorials on the current versions of C# 4 & WPF 4 and also general advice on the best approach. The application will do several things one of them would persisting info in a SQL DB. So Im thinking LINQ for that? Please chip in...

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