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Articles indexed in April 2010

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  • C/C++ enums: Detect when multiple items map to same value

    - by Dan
    Is there a compile-time way to detect / prevent duplicate values within a C/C++ enumeration? The catch is that there are multiple items which are initialized to explicit values. Background: I've inherited some C code such as the following: #define BASE1_VAL (5) #define BASE2_VAL (7) typedef enum { MsgFoo1A = BASE1_VAL, // 5 MsgFoo1B, // 6 MsgFoo1C, // 7 MsgFoo1D, // 8 MsgFoo1E, // 9 MsgFoo2A = BASE2_VAL, // Uh oh! 7 again... MsgFoo2B // Uh oh! 8 again... } FOO; The problem is that as the code grows & as developers add more messages to the MsgFoo1x group, eventually it overruns BASE2_VAL. This code will eventually be migrated to C++, so if there is a C++-only solution (template magic?), that's OK -- but a solution that works with C and C++ is better.

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  • Cache the result of a MySQLdb database query in memory

    - by ensnare
    Our application fetches the correct database server from a pool of database servers. So each query is really 2 queries, and they look like this: Fetch the correct DB server Execute the query We do this so we can take DB servers online and offline as necessary, as well as for load-balancing. But the first query seems like it could be cached to memory, so it only actually queries the database every 5 or 10 minutes or so. What's the best way to do this? Thanks.

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  • How does a virtual machine work?

    - by Martin
    I've been looking into how programming languages work, and some of them have a so-called virtual machines. I understand that this is some form of emulation of the programming language within another programming language, and that it works like how a compiled language would be executed, with a stack. Did I get that right? With the proviso that I did, what bamboozles me is that many non-compiled languages allow variables with "liberal" type systems. In Python for example, I can write this: x = "Hello world!" x = 2**1000 Strings and big integers are completely unrelated and occupy different amounts of space in memory, so how can this code even be represented in a stack-based environment? What exactly happens here? Is x pointed to a new place on the stack and the old string data left unreferenced? Do these languages not use a stack? If not, how do they represent variables internally?

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  • Printing HTML blocks

    - by Lem0n
    I have a page with a few tables that I want to be printable. I want the following behaviour: 1) Add a page break if the next table fits in a single page, but won't fit in the current page (because of other stuff already printed on this page) 2) Print the "table header" again in case it's needed to break a table (I guess it's the default behaviour) Any ideas specially on the first issue? Maybe some CSS can help? I'll give on example. I have a page with 4 tables. All of them with 10 lines, except the third one, with 50 lines. The first and second goes on the first page. Since the third one won't fit in the same page, but will fit in a page alone, it's printed on a page alone... and then the forth table is printed on the third page (in case it doesn't fit together in the second page). But, if the third page had 300 lines and would be broke anyway, it could have started to be print in the first page.

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  • Which languages are dynamically typed and compiled (and which are statically typed and interpreted)?

    - by Skilldrick
    In my reading on dynamic and static typing, I keep coming up against the assumption that statically typed languages are compiled, while dynamically typed languages are interpreted. I know that in general this is true, but I'm interested in the exceptions. I'd really like someone to not only give some examples of these exceptions, but try to explain why it was decided that these languages should work in this way.

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  • Imperative Programming in F#

    This article is taken from the book F# in Action. The authors discuss basics of imperative programming in F# and develop a simple application to show how this type of programming works. They also feature some of the interoperability among languages on .NET platform.

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  • Build Environment setup - Using .net, java, hudson, and ruby - Could really use a critique

    - by Jeff D
    I'm trying to figure out the best way to stitch together a fast, repeatable, unbreakable build process for the following environment. I've got a plan for how to do it, but I'd really appreciate a critique. (I'd also appreciate some sample code, but more on that later) Ecosystem - Logical: Website - asp.net MVC 2, .net 3.5, Visual Studio 2010. IIS 6, Facebook iframe application application. This website/facebook app uses a few services. An internal search api, an internal read/write api, facebook, and an IP geolocation service. More details on these below Internal search api - .net, restful, built using old school .ashx handlers. The api uses lucene, and a sql server database behind the scenes. My project won't touch the lucene code, but does potentially touch the database and the web services. internal read/write api - java, restful, running on Tomcat Facebook web services A mocking site that emulates the internal read/write api, and parts of the facebook api Hudson - Runs unit tests on checkin, and creates some installers that behave inconsistently. Ecosystem - Physical: All of these machines can talk to one another, except for Hudson. Hudson can't see any of the target machines. So code must be pulled, rather than pushed. (Security thing) 1. Web Server - Holds the website, and the read/write api. (The api itself writes to a replicated sql server environment). 2. Search Server - Houses the search api. 3. Hudson Server - Does not have permissions to push to any environment. They have to pull. 4. Lucene Server 5. Database Server Problem I've been trying to set this site up to run in a stress environment, but the number of setup steps, the amount of time it takes to update a component, the black-box nature of the current installers, and the time it takes to generate data into the test system is absolutely destroying my productivity. I tweak one setting, have to redeploy, restart in a certain order, resetup some of the settings, and rebuild test data. Errors result in headscratching, and then basically starting over. Very bad. This problem is complicated further by my stress testing. I need to be able to turn on and off different external components, so that I can effectively determine the scalability of each piece. I've got strategies in place for how to do that for each dependency, but it further complicates my setup strategy, because now each component has 2 options. A mock version, or a real version. Configurations everywhere must be updated accordingly. Goals Fast - I want to drop this from a 20 minute exercise when things go perfectly, to a 3 minute one Stupid simple - I want to tell the environment what to do with as few commands as possible, and not have to remember how to stitch the environments together Repeatable - I want the script to be idempotent. Kind of a corollary to the Stupid Simple thing. The Plan So Far Here's what I've come up with so far, and what I've come looking for feedback on: Use VisualStudio's new web.config transformations to permit easily altering configs based on envrionment. This solution isn't really sufficient though. I will leave web.config set up to let the site run locally, but when deploying elsewhere, I have as many as 6 different possible outputs for the stress environment alone (because of the mocks of the various dependencies), let alone the settings for prod, QA, and dev. Each of these would then require it's own setup, or a setup that would then post-process the configs. So I'm currently leaning toward just having the dev version, and a version that converts key configuration values into a ruby string interpolation syntax. ({#VAR_NAME} kinda thing) Create a ruby script for each server that is essentially a bootstrapping script. That is to say, it will do nothing but load the ruby code that does the 'real' work from hudson/subversion, so that the script's functionality can evolve with the application, making it easy to build the site at any point in time by reference the appropriate version of the script. So in a nutshell, this script loads another script, and runs it. The 'real' ruby script will then accept commandline parameters that describe how the environment should look. From there, 1 configuration file can be used, and ruby will download the current installers, run them, post-process the configs, restart IIS/Tomcat, and kick off any data setup code that is needed. So that's it. I'm in a real time crunch to get this site stress-tested, so any feedback that you think could abbreviate the time this might take would be appreciated. That includes a shameless request for sample ruby code. I've not gotten too much further than puts "Hello World". :-) Just guidance would be helpful. Is this something that Rake would be useful for? How would you recommend I write tests for this animal? (I use interfaces and automocking frameworks to mock out things like http requests in .net. With ducktyping, it seems that this might be easier, but I don't know how to tell my code to use a fake duck in test, but a real one in practice) Thanks all. Sorry for such such a long-winded, open-ended question.

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  • MySQL GROUP_CONCAT + IN() = missing data :-(

    - by Andrew Heath
    Example: Table: box boxID color 01 red 02 blue 03 green Table: boxHas boxID has 01 apple 01 pear 01 grapes 01 banana 02 lime 02 apple 02 pear 03 chihuahua 03 nachos 03 baby crocodile I want to query on the contents of each box, and return a table with each ID, color, and a column that concatenates the contents of each box, so I use: SELECT box.boxID, box.color, GROUP_CONCAT(DISTINCT boxHas.has SEPARATOR ", ") AS contents FROM box LEFT JOIN boxHas ON box.boxID=boxHas.boxID WHERE boxHas.has IN ('apple','pear') GROUP BY box.boxID ORDER BY box.boxID and I get the following table of results: boxID color contents 01 red apple, pear 02 blue apple, pear My question to you is: why isn't it listing ALL the has values in the contents column? Why is my WHERE statement also cropping my GROUP_CONCAT? The table I thought I was going to get is: boxID color contents 01 red apple, banana, grapes, pear 02 blue apple, lime, pear Although I want to limit my boxID results based upon the WHERE statement, I do not want to limit the contents field for valid boxes. :-/ Help?

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  • Finding the "name" of your Android application.

    - by fiXedd
    Is there any way to (programatically) find out what your app's name is? I'm specifically talking about the android:label property from the application tag in the manifest file: <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.test" android:versionCode="1" android:versionName="1.0"> <application android:label="THIS THING HERE!" android:icon="@drawable/icon"> <!-- ... --> </application> </manifest>

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  • SQL Server switch to MySQL/PostgreSQL for startup?

    - by chopps
    I just checked out the licensing for SQL Server and well...i can't afford it since im funding this project myself. I have been tinkering with MySQL and PostgreSQL a bit the past few weeks and at this point I can't really decide which to go with. MySQL has a large user base and lots of people using it so finding out how to do various items will not be to hard o find. I will be using ASP.NET with this project. Anyone have experience going from SQL Server to either of these databases? Is one stronger than the other? Thoughts?

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  • How send sms 2automatically 2 a paricular no: only?

    - by royalcasanova
    import net.rim.device.api.io.; import net.rim.device.api.system.; import javax.microedition.io.; import java.util.; import java.io.*; public class SendSms extends Application { private static final int MAX_PHONE_NUMBER_LENGTH = 32; private String addr = "15191112222"; private String msg = "This is a test message."; private DatagramConnection _dc = null; private static String _openString = "sms://"; public static void main(String[] args) { new SendSms().enterEventDispatcher(); } public SendSms() { try { _dc = (DatagramConnection)Connector.open(_openString); byte[] data = msg.getBytes(); Datagram d = _dc.newDatagram(_dc.getMaximumLength()); d.setAddress("//" + addr); _dc.send(d); } catch ( IOException e) {} System.exit(0); } }

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  • ASP.NET plugin architecture for SaaS?

    - by chopps
    Hey Everyone, Been doing a bit of research and have a few questions about using a Plugin architecture for asp.net. I have used it before for a single application and works well but was wondering if it technically possible to use this architecture for a SaaS? Once code base but custom plugins for each customer using some form of custom folders to organize the plugins? Idea would be to use one main code base instead of having to maintain code for N number of clients. Ideas? Thoughts? Experience either way?

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  • No cursor when resizing datagridview c#

    - by anya
    HI guys, When im trying to resize datagridview columns the resize cursor appears only when i roll over header. However, when i roll over in between cells, resize cursor doesnt show at all. I have noticed if i set ColumnHeadersVisible = false it fixes the problem and i see resize cursor between columns. However, i need header to be visible, any idea how to make it work all together? Thanks!

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  • Builder pattern and singletons

    - by Berryl
    Does anyone have any links to some code they like that shows a good example of this in c#? As an example of bad code, here is what a builder I have now looks like. I'm trying to have a way to keep the flexibility of the builder pattern but not rebuild the properties. Cheers, Berryl public abstract class ActivityBuilder { public abstract ActivityBuilder Build(); public bool IsBuilt { get; protected set; } public IEnumerable<Project> Projects { get { if(_projects==null) { Build(); } return _projects; } } protected IEnumerable<Project> _projects; // .. other properties }

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  • Has anyone gotten VB highlighting to work in Emacs23?

    - by akoumjian
    I have found and installed the visual basic mode for emacs. It seems to be loading on emacs startup and the VB mode loads when I open a *.bas file. The code is not highlighted at all, however. I'm using Emacs23, tried it with 21 and saw no difference. Background for the curious: I am rewriting a set of codes from VB to Python. The syntax highlighting will make it much easier for me to see what's going on.

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  • redis timeout with predis

    - by Patrick
    Hello, I'm using redis with php (predis at http://github.com/nrk/predis/) and am experiencing frequent timeout. The stack trace shows: [04-Apr-2010 03:39:50] PHP Fatal error: Uncaught exception 'Predis_ClientException' with message 'Connection timed out' in redis.php:697 Stack trace: #0 redis.php(757): Predis_Connection->connect() #1 redis.php(729): Predis_Connection->getSocket() #2 redis.php(825): Predis_Connection->writeCommand(Object(Predis_Commands_ListRange)) #3 redis.php(165): Predis_ConnectionCluster->writeCommand(Object(Predis_Commands_ListRange)) #4 redis.php(173): Predis_Client->executeCommandInternal(Object(Predis_ConnectionCluster), Object(Predis_Commands_ListRange)) #5 redis.php(157): Predis_Client->executeCommand(Object(Predis_Commands_ListRange)) #6 [internal function]: Predis_Client->__call('lrange', Array) This happens consistently and I have no idea why. Anyone has any idea?

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  • CSS Design question, I've got myself completely turned around.

    - by Matt Dawdy
    Okay, I have a couple of other questions out there, but I think I'd better just ask from the beginning how you CSS experts would do this. Client's page is split into 2 rows -- header has some info, some aligned to left of page, some to right, some in the middle. This is currently done using a table. I'm fine with leaving this alone or changing it. My real question is that I need a page layout to handle the following: 2 columns - column on left is 200px, but can be "close" down to to 10px (not a slider, it's either 200 or 10 px). The column on the right needs to be as big as it needs to be -- which might be larger than the width of the page. When left column is "closed" then the right column slides over of course. Again, this right column might be 300px or it might be 4000 pixels (it's a reporting interface). Now, to add another wrinkle, SOME pages have 3 columns. The first 2 columns are each exactly 200px, and both can be "closed" down to 10 px each. But, the user may not close both columns, maybe just 1. Or none. Or both. The third column needs to act just like I described above, being able to be larger than the page width, and sliding over to take advantage of any of the "closed" left columns. Whew! I'm pretty confused as to how to go about this, as either I get it right but I can't scroll over to the right at all (overflow: hidden) and information is lost, or the right column jumps down below the left 2 columns and just looks plain stupid. My minimum browser requirements are IE8, FF3.5, Chrome and Safari (latest versions of all). Any and all pointers are gladly accepted.

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  • VMWare Fusion patch to install Snow Leopard client

    - by Michael
    I'm running VMWare Fusion on Snow Leopard. I'm looking for instructions on how to patch the VMWare settings files so it will let me install Snow Leopard client as a guest OS. Please Note: Links to hacks on how to do this is not allowed on SU. Only officially sanctioned Apple or VMWare solutions are allowed. Any other solutions will be deleted.

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  • how do I call create a name of a button variable in a code, with a number in it? (hard to explain)

    - by Sam Jarman
    Ive got a int, that is changed in a previous method, that now has to be part of the name of a button variable eg int numberFromLastOne; numberFromLastOne = 4; I then want to get 'button4' to do something. Could i use something like this? [[button@"%d", numberFromLastOne] doSomethign:withSomethignElse]; Ive never had to do something this before.... Any ideas would be appreciated :) Sam

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  • Python socket error on UDP data receive. (10054)

    - by Charles
    I currently have a problem using UDP and Python socket module. We have a server and clients. The problem occurs when we send data to a user. It's possible that user may have closed their connection to the server through a client crash, disconnect by ISP, or some other improper method. As such, it is possible to send data to a closed socket. Of course with UDP you can't tell if the data really reached or if it's closed, as it doesn't care (atleast, it doesn't bring up an exception). However, if you send data and it is closed off, you get data back somehow (???), which ends up giving you a socket error on sock.recvfrom. [Errno 10054] An existing connection was forcibly closed by the remote host. Almost seems like an automatic response from the connection. Although this is fine, and can be handled by a try: except: block (even if it lowers performance of the server a little bit). The problem is, I can't tell who this is coming from or what socket is closed. Is there anyway to find out 'who' (ip, socket #) sent this? It would be great as I could instantly just disconnect them and remove them from the data. Any suggestions? Thanks.

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