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  • Why is it still so hard to write software?

    - by nornagon
    Writing software, I find, is composed of two parts: the Idea, and the Implementation. The Idea is about thinking: "I have this problem; how do I solve it?" and further, "how do I solve it elegantly?" The answers to these questions are obtainable by thinking about algorithms and architecture. The ideas come partially through analysis and partially through insight and intuition. The Idea is usually the easy part. You talk to your friends and co-workers and you nut it out in a meeting or over coffee. It takes an hour or two, plus revisions as you implement and find new problems. The Implementation phase of software development is so difficult that we joke about it. "Oh," we say, "the rest is a Simple Matter of Code." Because it should be simple, but it never is. We used to write our code on punch cards, and that was hard: mistakes were very difficult to spot, so we had to spend extra effort making sure every line was perfect. Then we had serial terminals: we could see all our code at once, search through it, organise it hierarchically and create things abstracted from raw machine code. First we had assemblers, one level up from machine code. Mnemonics freed us from remembering the machine code. Then we had compilers, which freed us from remembering the instructions. We had virtual machines, which let us step away from machine-specific details. And now we have advanced tools like Eclipse and Xcode that perform analysis on our code to help us write code faster and avoid common pitfalls. But writing code is still hard. Writing code is about understanding large, complex systems, and tools we have today simply don't go very far to help us with that. When I click "find all references" in Eclipse, I get a list of them at the bottom of the window. I click on one, and I'm torn away from what I was looking at, forced to context switch. Java architecture is usually several levels deep, so I have to switch and switch and switch until I find what I'm really looking for -- by which time I've forgotten where I came from. And I do that all day until I've understood a system. It's taxing mentally, and Eclipse doesn't do much that couldn't be done in 1985 with grep, except eat hundreds of megs of RAM. Writing code has barely changed since we were staring at amber on black. We have the theoretical groundwork for much more advanced tools, tools that actually work to help us comprehend and extend the complex systems we work with every day. So why is writing code still so hard?

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  • WordPress Write Cache Problem with Multiple Sessions

    - by Volomike
    I'm working on a content dripper custom plugin in WordPress that my client asked me to build. He says he wants it to catch a page view event, and if it's the right time of day (24 hours since last post), to pull from a resource file and output another post. He needed it to also raise a flag and prevent other sessions from firing that same snippet of code. So, raise some kind of flag saying, "I'm posting that post, go away other process," and then it makes that post and releases the flag again. However, the strangest thing is occurring when placed under load with multiple sessions hitting the site with page views. It's firing instead of one post -- it's randomly doing like 1, 2, or 3 extra posts, with each one thinking that it was the right time to post because it was 24 hours past the time of the last post. Because it's somewhat random, I'm guessing that the problem is some kind of write caching where the other sessions don't see the raised flag just yet until a couple microseconds pass. The plugin was raising the "flag" by simply writing to the wp_options table with the update_option() API in WordPress. The other user sessions were supposed to read that value with get_option() and see the flag, and then not run that piece of code that creates the post because a given session was already doing it. Then, when done, I lower the flag and the other sessions continue as normal. But what it's doing is letting those other sessions in. To make this work, I was using add_action('loop_start','checkToAddContent'). The odd thing about that function though is that it's called more than once on a page, and in fact some plugins may call it. I don't know if there's a better event to hook. Even still, even if I find an event to hook that only runs once on a page view, I still have multiple sessions to contend with (different users who may view the page at the same time) and I want only one given session to trigger the content post when the post is due on the schedule. I'm wondering if there are any WordPress plugin devs out there who could suggest another event hook to latch on to, and to figure out another way to raise a flag that all sessions would see. I mean, I could use the shared memory API in PHP, but many hosting plans have that disabled. Can't use a cookie or session var because that's only one single session. About the only thing that might work across hosting plans would be to drop a file as a flag, instead. If the file is present, then one session has the flag. If the file is not present, then other sessions can attempt to get the flag. Sure, I could use the file route, but it's kind of immature in my opinion and I was wondering if there's something in WordPress I could do.

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  • Arguments for moving from LINQtoSQL to Nhibernate?

    - by sah302
    Backstory: Hi all, I just spent a lot of time reading many of the LINQ vs Nhibernate threads here and on other sites. I work in a small development team of 4 people and we don't even have really any super experienced developers. We work for a small company that has a lot of technical needs but not enough developers to implement them (and hiring more is out of the question right now). Typically our projects (which individually are fairly small) have been coded separately and weren't really layered in anyway, code wasn't re-used, no class libraries, and we just use the LINQtoSQL .dbml files for our pojects, we really don't even use objects but pass around values and stuff, the only time we use objects is when inserting to a database (heck not even querying since you don't need to assign it to a type and can just bind to gridview). Despite all this as I said our company has a lot of technical needs, no one could come to us for a year and we would have plenty of work to implement requested features. Well I have decided to change that a bit first by creating class libraries and actually adding layers to our applications. I am trying to meet these guys halfway by still using LINQtoSQL as the ORM yet and still use VB as the language. However I am finding it a b***h of a time dealing with so many thing in LINQtoSQL that I found easy in Nhibernate (automatic handling of the session, criteria creation easier than expression trees, generic an dynamic querying easier etc.) So... Question: How can I convince my lead developers and other senior programmers that switching to Nhibernate is a good thing? That being in control of our domain objects is a good thing? That being able to implement interfaces is a good? I've tried exlpaining the advantages of this before but it's not understood by them because they've never programmed in a true OO & layered way. Also one of the counter arguments to this I can see is sqlMetal generates those classes automatically and therefore it saves a lot of time. I can't really counter that other than saying spending more time on infrastructure to make it more scalable and flexible is good, but they can't see how. Again, I know the features and advantages (somewhat enough I believe) of each, but I need arguments applicable to my context, hence why I provided the context. I just am not a very good arguer I guess. (Caveat: For all the LINQtoSQL lovers, I may just not be super proficient as LINQ, but I find it very cumbersome that you are required to download some extra library for dynamic queries which don't by default support guid comparisons, and I also find the way of updating entitites to be cumbersome as well in terms of data context managing, so it could just be that I suck hehe.)

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  • Various GPS Android Functionality Questions..

    - by Tyler
    Hello - I have a few questions (so far) with the the LocationManager on Android and GPS in general.. Feel free to answer any number of the questions below, and I appreciate your help in advance! (I noticed this stuff doesn't appear to be documented very well, so hopefully these questions will help others out too!) 1) I am using the following code, but I think there may be extra fluff in here that I do not need. Can you tell me if I can delete any of this? LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); LocationListener locationListener = new MyLocationListener(); lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener); LocationProvider locationProvider = lm.getProvider("gps"); Location currentLocation = lm.getLastKnownLocation(locationProvider.getName()); 2) Is there a way to hold off on the last step (accessing "getLastKnownLocation" until after I am sure I have a GPS lock? What happens if this is called and GPS is still looking for signal? 3) MOST importantly, I want to ensure I have a GPS lock before I proceed to my next method, so is there a way to check to see if GPS is locked on and getLastKnownLocation is up to date? 4) Is there a way to 'shut down' the GPS listener once it does receive a lock and getLastKnownLocation is updated? I don't see a need to keep this running for my application once I have obtained a lock.. 5) Can you please confirm my assumption that "getLastKnownLocation" is updated frequently as the receiver moves? 6) In my code, I also have a class called "MyLocationListener" (code below) that I honestly just took from another example.. Is this actually needed? I assume this updates my location manager whenever the location changes, but it sure doesn't appear that there is much to the class itself! private class MyLocationListener implements LocationListener { @Override public void onLocationChanged(Location loc) { if (loc != null) { //Toast.makeText(getBaseContext(), "Location changed : Lat: " + loc.getLatitude() + " Lng: " + loc.getLongitude(), Toast.LENGTH_SHORT).show(); } } @Override public void onProviderDisabled(String provider) { // TODO Auto-generated method stub } @Override public void onProviderEnabled(String provider) { // TODO Auto-generated method stub } @Override public void onStatusChanged(String provider, int status, Bundle extras) { // TODO Auto-generated method stub } }

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  • do I need to close an audio Clip?

    - by Michael
    have an application that processes real-time data and is supposed to beep when a certain event occurs. The triggering event can occur multiple times per second, and if the beep is already playing when another event triggers the code is just supposed to ignore it (as opposed to interrupting the current beep and starting a new one). Here is the basic code: Clip clickClip public void prepareProcess() { super.prepareProcess(); clickClip = null; try { clipFile = new File("C:/WINDOWS/Media/CHIMES.wav"); ais = AudioSystem.getAudioInputStream(clipFile); clickClip = AudioSystem.getClip(); clickClip.open(ais); fileIsLoaded = true; } catch (Exception ex) { clickClip = null; fileIsLoaded = false; } } public void playSound() { if (fileIsLoaded) { if ((clickClip==null) || (!clickClip.isRunning())) { try { clickClip.setFramePosition(0); clickClip.start(); } catch (Exception ex) { System.out.println("Cannot play click noise"); ex.printStackTrace(); } } } The prepareProcess method gets run once in the beginning, and the playSound method is called every time a triggering event occurs. My question is: do I need to close the clickClip object? I know I could add an actionListener to monitor for a Stop event, but since the event occurs so frequently I'm worried the extra processing is going to slow down the real-time data collection. The code seems to run fine, but my worry is memory leaks. The code above is based on an example I found while searching the net, but the example used an actionListener to close the Clip specifically "to eliminate memory leaks that would occur when the stop method wasn't implemented". My program is intended to run for hours so any memory leaks I have will cause problems. I'll be honest: I have no idea how to verify whether or not I've got a problem. I'm using Netbeans, and running the memory profiler just gave me a huge list of things that I don't know how to read. This is supposed to be the simple part of the program, and I'm spending hours on it. Any help would be greatly appreciated! Michael

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  • Help to understand and recode javascript function to deal with special characters.

    - by Cesar Lopez
    Hi all, I am trying to rewrite a javascript function since I was told this function its a bit nasty peace of code and it could be nicely written by a very kind user from here. I have been trying to understand what the function does, therefore I could rewrite it properly, but since I dont fully understand how it works its a very difficult task. Therefore I am looking for help and directions (NOT THE SOLUTION AS I WANT TO LEARN MYSELF) to understand and rewrite this function in a nicer way. The function its been made for dealing with special characters, and I know that it loops through the string sent to it, search for special characters, and add what it needs to the string to make it a valid string. I have been trying to use value.replace(/"/gi,"/""), but surely I am doing it wrong as it crashes. Could anybody tell me where to start to recode function? Any help would be appreciated. My comments on the function are in capital letters. Code <script type="text/javascript"> function convertString(value){ for(var z=0; z <= value.length -1; z++) { //if current character is a backslash||WHY IS IT CHECKING FOR \\,\\r\\n,and \\n? if(value.substring(z, z + 1)=="\\" && (value.substring(z, z + 4)!="\\r\\n" && value.substring(z, z + 2)!="\\n")) {//WHY IS IT ADDING \\\\ TO THE STRING? value = value.substring(0, z) + "\\\\" + value.substring(z + 1, value.length); z++; } if(value.substring(z, z + 1)=="\\" && value.substring(z, z + 4)=="\\r\\n") {//WHY IS IT ADDING 4 TO Z IN THIS CASE? z = z+4; } if(value.substring(z, z + 1)=="\\" && value.substring(z, z + 2)=="\\n") {//WHY IS IT ADDING 2 TO Z IN THIS CASE? z = z+2; } } //replace " with \" //loop through each character for(var x = 0; x <= value.length -1; x++){ //if current character is a quote if(value.substring(x, x + 1)=="\""){//THIS IS TO FIND \, BUT HAVENT THIS BEEN DONE BEFFORE? //concatenate: value up to the quote + \" + value AFTER the quote||WHY IS IT ADDING \\ BEFORE \"? value = value.substring(0, x) + "\\\"" + value.substring(x + 1, value.length); //account for extra character x++; } } //return the modified string return(value); } <script> Comments within the code on capital letters are my questions about the function as I mention above. I would appreciate any help, orientation, advise, BUT NOT THE SOLUTION PLEASE AS I DO WANT TO LEARN.

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  • Which MarkDown (WMD) javascript editor should I use?

    - by Edan Maor
    Background I'm working on an application which requires user-entered content, and I've decided to use a StackOverflow-style MarkDown editor. After researching this topic for the last few days, I realize there are numerous forks of the base WMD editor, some with a few basic enhancements and some with serious differences from the StackOverflow one. Since this will be the heart of the application, I'd like to start with the best code base I can. I'd be happy if anyone can recommend which one of the many solutions out there best fits my needs. Below is requirements, plus what I've managed to find already. I'm hoping this question will help me decide which version to go with, and maybe help me discover a port out there that's an even better fit for my needs. The requirements for my project Live Preview Multiple editors on the same page (not know how many in advance, since the user can dynamically add another editing box). Ability to extend with extra buttons (I'd like a button to upload a picture, instead of just adding an img url). Ability to dynamically show/hide the edit box (and only see the preview box). Not an absolute must, but I'd prefer to stick as close to StackOverflow's look and feel, since it's well known. Don't know if this matters, but the backend is written in Django. Editors I've looked at Here are a few of the code bases I've looked at, with thoughts. Obviously, I might be missing another solution out there. The derobins version. From what I can tell, this is the official StackOverflow version. Seems like it doesn't support multiple editors on one page. JQuery.MarkEdit. Looks very good, but is pretty different from the StackOverflow version. MooWMD. Looks like the winner right now, but I'm a little concerned since it looks less active/hackable than MarkEdit. The wmd-new version. Not sure, looks like an old codebase without much use. The SocialSite branch. Seems like it's not for public use.

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  • How to combine designable components with dependency injection

    - by Wim Coenen
    When creating a designable .NET component, you are required to provide a default constructor. From the IComponent documentation: To be a component, a class must implement the IComponent interface and provide a basic constructor that requires no parameters or a single parameter of type IContainer. This makes it impossible to do dependency injection via constructor arguments. (Extra constructors could be provided, but the designer would ignore them.) Some alternatives we're considering: Service Locator Don't use dependency injection, instead use the service locator pattern to acquire dependencies. This seems to be what IComponent.Site.GetService is for. I guess we could create a reusable ISite implementation (ConfigurableServiceLocator?) which can be configured with the necessary dependencies. But how does this work in a designer context? Dependency Injection via properties Inject dependencies via properties. Provide default instances if they are necessary to show the component in a designer. Document which properties need to be injected. Inject dependencies with an Initialize method This is much like injection via properties but it keeps the list of dependencies that need to be injected in one place. This way the list of required dependencies is documented implicitly, and the compiler will assists you with errors when the list changes. Any idea what the best practice is here? How do you do it? edit: I have removed "(e.g. a WinForms UserControl)" since I intended the question to be about components in general. Components are all about inversion of control (see section 8.3.1 of the UMLv2 specification) so I don't think that "you shouldn't inject any services" is a good answer. edit 2: It took some playing with WPF and the MVVM pattern to finally "get" Mark's answer. I see now that visual controls are indeed a special case. As for using non-visual components on designer surfaces, I think the .NET component model is fundamentally incompatible with dependency injection. It appears to be designed around the service locator pattern instead. Maybe this will start to change with the infrastructure that was added in .NET 4.0 in the System.ComponentModel.Composition namespace.

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  • Why does extend() engage in bizarre behaviour when passed the same list twice?

    - by intuited
    I'm pretty confused by one of the subtleties of the vimscript extend() function. If you use it to extend a list with another list, it does pretty much what you'd expect, which is to insert the second list into the first list at the index given by the third parameter: let list1 = [1,2,3,4,5,6] | echo extend(list1,[1,2,3,4,5,6],5) " [1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6, 6] However if you give it the same list twice it starts tripping out a bit. let list1 = [1,2,3,4,5,6] | echo extend(list1,list1,0) " [1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6] let list1 = [1,2,3,4,5,6] | echo extend(list1,list1,1) " [1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 5, 6] let list1 = [1,2,3,4,5,6] | echo extend(list1,list1,2) " [1, 2, 1, 2, 1, 2, 1, 2, 3, 4, 5, 6] let list1 = [1,2,3,4,5,6] | echo extend(list1,list1,3) " [1, 2, 3, 1, 2, 3, 1, 2, 3, 4, 5, 6] let list1 = [1,2,3,4,5,6] | echo extend(list1,list1,4) " [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 5, 6] let list1 = [1,2,3,4,5,6] | echo extend(list1,list1,5) " [1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 6] let list1 = [1,2,3,4,5,6] | echo extend(list1,list1,6) " [1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6] Extra-confusingly, this behaviour applies when the list is referenced with two different variables: let list1 = [1,2,3,4,5,6] | let list2 = list1 | echo extend(list1,list2,4) " [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 5, 6] This is totally bizarre to me. I can't fathom a use for this functionality, and it seems like it would be really easy to invoke it by accident when you just wanted to insert one list into another and didn't realize that the variables were referencing the same array. The documentation says the following: If they are |Lists|: Append {expr2} to {expr1}. If {expr3} is given insert the items of {expr2} before item {expr3} in {expr1}. When {expr3} is zero insert before the first item. When {expr3} is equal to len({expr1}) then {expr2} is appended. Examples: :echo sort(extend(mylist, [7, 5])) :call extend(mylist, [2, 3], 1) When {expr1} is the same List as {expr2} then the number of items copied is equal to the original length of the List. E.g., when {expr3} is 1 you get N new copies of the first item (where N is the original length of the List). Does this make sense in a way that I'm not getting, or is it just an eccentricity?

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  • Choosing a distributed shared memory solution

    - by mindas
    I have a task to build a prototype for a massively scalable distributed shared memory (DSM) app. The prototype would only serve as a proof-of-concept, but I want to spend my time most effectively by picking the components which would be used in the real solution later on. The aim of this solution is to take data input from an external source, churn it and make the result available for a number of frontends. Those "frontends" would just take the data from the cache and serve it without extra processing. The amount of frontend hits on this data can literally be millions per second. The data itself is very volatile; it can (and does) change quite rapidly. However the frontends should see "old" data until the newest has been processed and cached. The processing and writing is done by a single (redundant) node while other nodes only read the data. In other words: no read-through behaviour. I was looking into solutions like memcached however this particular one doesn't fulfil all our requirements which are listed below: The solution must at least have Java client API which is reasonably well maintained as the rest of app is written in Java and we are seasoned Java developers; The solution must be totally elastic: it should be possible to add new nodes without restarting other nodes in the cluster; The solution must be able to handle failover. Yes, I realize this means some overhead, but the overall served data size isn't big (1G max) so this shouldn't be a problem. By "failover" I mean seamless execution without hardcoding/changing server IP address(es) like in memcached clients when a node goes down; Ideally it should be possible to specify the degree of data overlapping (e.g. how many copies of the same data should be stored in the DSM cluster); There is no need to permanently store all the data but there might be a need of post-processing of some of the data (e.g. serialization to the DB). Price. Obviously we prefer free/open source but we're happy to pay a reasonable amount if a solution is worth it. In any way, paid 24hr/day support contract is a must. The whole thing has to be hosted in our data centers so SaaS offerings like Amazon SimpleDB are out of scope. We would only consider this if no other options would be available. Ideally the solution would be strictly consistent (as in CAP); however, eventual consistence can be considered as an option. Thanks in advance for any ideas.

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  • How can I limit the cache used by copying so there is still memory available for other cache?

    - by Peter
    Basic situation: I am copying some NTFS disks in openSuSE. Each one is 2TB. When I do this, the system runs slow. My guesses: I believe it is likely due to caching. Linux decides to discard useful cache (eg. kde4 bloat, virtual machine disks, LibreOffice binaries, Thunderbird binaries, etc.) and instead fill all available memory (24 GB total) with stuff from the copying disks, which will be read only once, then written and never used again. So then any time I use these apps (or kde4), the disk needs to be read again, and reading the bloat off the disk again makes things freeze/hiccup. Due to the cache being gone and the fact that these bloated applications need lots of cache, this makes the system horribly slow. Since it is USB,the disk and disk controller are not the bottleneck, so using ionice does not make it faster. I believe it is the cache rather than just the motherboard going too slow, because if I stop everything copying, it still runs choppy for a while until it recaches everything. And if I restart the copying, it takes a minute before it is choppy again. But also, I can limit it to around 40 MB/s, and it runs faster again (not because it has the right things cached, but because the motherboard busses have lots of extra bandwidth for the system disks). I can fully accept a performance loss from my motherboard's IO capability being completely consumed (which is 100% used, meaning 0% wasted power which makes me happy), but I can't accept that this caching mechanism performs so terribly in this specific use case. # free total used free shared buffers cached Mem: 24731556 24531876 199680 0 8834056 12998916 -/+ buffers/cache: 2698904 22032652 Swap: 4194300 24764 4169536 I also tried the same thing on Ubuntu, which causes a total system hang instead. ;) And to clarify, I am not asking how to leave memory free for the "system", but for "cache". I know that cache memory is automatically given back to the system when needed, but my problem is that it is not reserved for caching of specific things. Question: Is there some way to tell these copy operations to limit memory usage so some important things remain cached, and therefore any slowdowns are a result of normal disk usage and not rereading the same commonly used files? For example, is there a setting of max memory per process/user/file system allowed to be used as cache/buffers?

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  • Why does my ko computed observable not update bound UI elements when its value changes?

    - by Allen
    I'm trying to wrap a cookie in a computed observable (which I'll later turn into a protectedObservable) and I'm having some problems with the computed observable. I was under the opinion that changes to the computed observable would be broadcast to any UI elements that have been bound to it. I've created the following fiddle JavaScript: var viewModel = {}; // simulating a cookie store, this part isnt as important var cookie = function () { // simulating a value stored in cookies var privateZipcode = "12345"; return { 'write' : function (val) { privateZipcode = val; }, 'read': function () { return privateZipcode; } } }(); viewModel.zipcode = ko.computed({ read: function () { return cookie.read(); }, write: function (value) { cookie.write(value); }, owner: viewModel }); ko.applyBindings(viewModel);? HTML: zipcode: <input type='text' data-bind="value: zipcode"> <br /> zipcode: <span data-bind="text: zipcode"></span>? I'm not using an observable to store privateZipcode since that's really just going to be in a cookie. I'm hoping that the ko.computed will provide the notifications and binding functionality that I need, though most of the examples I've seen with ko.computed end up using a ko.observable underneath the covers. Shouldn't the act of writing the value to my computed observable signal the UI elements that are bound to its value? Shouldn't these just update? Workaround I've got a simple workaround where I just use a ko.observable along side of my cookie store and using that will trigger the required updates to my DOM elements but this seems completely unnecessary, unless ko.computed lacks the signaling / dependency type functionality that ko.observable has. My workaround fiddle, you'll notice that the only thing that changes is that I added a seperateObservable that isn't used as a store, its only purpose is to signal to the UI that the underlying data has changed. // simulating a cookie store, this part isnt as important var cookie = function () { // simulating a value stored in cookies var privateZipcode = "12345"; // extra observable that isnt really used as a store, just to trigger updates to the UI var seperateObservable = ko.observable(privateZipcode); return { 'write' : function (val) { privateZipcode = val; seperateObservable(val); }, 'read': function () { seperateObservable(); return privateZipcode; } } }(); This makes sense and works as I'd expect because viewModel.zipcode depends on seperateObservable and updates to that should (and does) signal the UI to update. What I don't understand, is why doesn't a call to the write function on my ko.computed signal the UI to update, since that element is bound to that ko.computed? I suspected that I might have to use something in knockout to manually signal that my ko.computed has been updated, and I'm fine with that, that makes sense. I just haven't been able to find a way to accomplish that.

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  • Django Multi-Table Inheritance VS Specifying Explicit OneToOne Relationship in Models

    - by chefsmart
    Hope all this makes sense :) I'll clarify via comments if necessary. Also, I am experimenting using bold text in this question, and will edit it out if I (or you) find it distracting. With that out of the way... Using django.contrib.auth gives us User and Group, among other useful things that I can't do without (like basic messaging). In my app I have several different types of users. A user can be of only one type. That would easily be handled by groups, with a little extra care. However, these different users are related to each other in hierarchies / relationships. Let's take a look at these users: - Principals - "top level" users Administrators - each administrator reports to a Principal Coordinators - each coordinator reports to an Administrator Apart from these there are other user types that are not directly related, but may get related later on. For example, "Company" is another type of user, and can have various "Products", and products may be supervised by a "Coordinator". "Buyer" is another kind of user that may buy products. Now all these users have various other attributes, some of which are common to all types of users and some of which are distinct only to one user type. For example, all types of users have to have an address. On the other hand, only the Principal user belongs to a "BranchOffice". Another point, which was stated above, is that a User can only ever be of one type. The app also needs to keep track of who created and/or modified Principals, Administrators, Coordinators, Companies, Products etc. (So that's two more links to the User model.) In this scenario, is it a good idea to use Django's multi-table inheritance as follows: - from django.contrib.auth.models import User class Principal(User): # # # branchoffice = models.ForeignKey(BranchOffice) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalmodifier") # # # Or should I go about doing it like this: - class Principal(models.Model): # # # user = models.OneToOneField(User, blank=True) branchoffice = models.ForeignKey(BranchOffice) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalmodifier") # # # Please keep in mind that there are other user types that are related via foreign keys, for example: - class Administrator(models.Model): # # # principal = models.ForeignKey(Principal, help_text="The supervising principal for this Administrator") user = models.OneToOneField(User, blank=True) province = models.ForeignKey( Province) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="administratorcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="administratormodifier") I am aware that Django does use a one-to-one relationship for multi-table inheritance behind the scenes. I am just not qualified enough to decide which is a more sound approach.

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  • Is do-notation specific to "base:GHC.Base.Monad"?

    - by yairchu
    The idea that the standard Monad class is flawed and that it should actually extend Functor or Pointed is floating around. I'm not necessarily claiming that it is the right thing to do, but suppose that one was trying to do it: import Prelude hiding (Monad(..)) class Functor m => Monad m where return :: a -> m a join :: m (m a) -> m a join = (>>= id) (>>=) :: m a -> (a -> m b) -> m b a >>= t = join (fmap t a) (>>) :: m a -> m b -> m b a >> b = a >>= const b So far so good, but then when trying to use do-notation: whileM :: Monad m => m Bool -> m () whileM iteration = do done <- iteration if done then return () else whileM iteration The compiler complains: Could not deduce (base:GHC.Base.Monad m) from the context (Monad m) Question: Does do-notation work only for base:GHC.Base.Monad? Is there a way to make it work with an alternative Monad class? Extra context: What I really want to do is replace base:Control.Arrow.Arrow with a "generalized" Arrow class: {-# LANGUAGE TypeFamilies #-} class Category a => Arrow a where type Pair a :: * -> * -> * arr :: (b -> c) -> a b c first :: a b c -> a (Pair a b d) (Pair a c d) second :: a b c -> a (Pair a d b) (Pair a d c) (***) :: a b c -> a b' c' -> a (Pair a b b') (Pair a c c') (&&&) :: a b c -> a b c' -> a b (Pair a c c') And then use the Arrow's proc-notation with my Arrow class, but that fails like in the example above of do-notation and Monad. I'll use mostly Either as my pair type constructor and not the (,) type constructor as with the current Arrow class. This might allow to make the code of my toy RTS game (cabal install DefendTheKind) much prettier.

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  • Autocomplete server-side implementation

    - by toluju
    What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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  • Passing Objects between different files

    - by user309779
    Typically, if I want to pass an object to an instance of something I would do it like so... Listing 1 File 1: public class SomeClass { // Some Properties public SomeClass() { public int ID { get { return mID; } set { mID = value; } } public string Name { set { mName = value; } get { return mName; } } } } public class SomeOtherClass { // Method 1 private void Method1(int one, int two) { SomeClass USER; // Create an instance Squid RsP = new Squid(); RsP.sqdReadUserConf(USER); // Able to pass 'USER' to class method in different file. } } In this example, I was not able to use the above approach. Probably because the above example passes an object between classes. Whereas, below, things are defined in a single class. I had to use some extra steps (trial & error) to get things to work. I am not sure what I did here or what its called. Is it good programming practice? Or is there is an easier way to do this (like above). Listing 2 File 1: private void SomeClass1 { [snip] TCOpt_fM.AutoUpdate = optAutoUpdate.Checked; TCOpt_fM.WhiteList = optWhiteList.Checked; TCOpt_fM.BlackList = optBlackList.Checked; [snip] private TCOpt TCOpt_fM; TCOpt_fM.SaveOptions(TCOpt_fM); } File 2: public class TCOpt: { public TCOpt OPTIONS; [snip] private bool mAutoUpdate = true; private bool mWhiteList = true; private bool mBlackList = true; [snip] public bool AutoUpdate { get { return mAutoUpdate; } set { mAutoUpdate = value; } } public bool WhiteList { get { return mWhiteList; } set { mWhiteList = value; } } public bool BlackList { get { return mBlackList; } set { mBlackList = value; } } [snip] public bool SaveOptions(TCOpt OPTIONS) { [snip] Some things being written out to a file here [snip] Squid soSwGP = new Squid(); soSgP.sqdWriteGlobalConf(OPTIONS); } } File 3: public class SomeClass2 { public bool sqdWriteGlobalConf(TCOpt OPTIONS) { Console.WriteLine(OPTIONS.WhiteSites); // Nothing prints here Console.WriteLine(OPTIONS.BlackSites); // Or here } } Thanks in advance, XO

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  • Mocking a concrete class : templates and avoiding conditional compilation

    - by AshirusNW
    I'm trying to testing a concrete object with this sort of structure. class Database { public: Database(Server server) : server_(server) {} int Query(const char* expression) { server_.Connect(); return server_.ExecuteQuery(); } private: Server server_; }; i.e. it has no virtual functions, let alone a well-defined interface. I want to a fake database which calls mock services for testing. Even worse, I want the same code to be either built against the real version or the fake so that the same testing code can both: Test the real Database implementation - for integration tests Test the fake implementation, which calls mock services To solve this, I'm using a templated fake, like this: #ifndef INTEGRATION_TESTS class FakeDatabase { public: FakeDatabase() : realDb_(mockServer_) {} int Query(const char* expression) { MOCK_EXPECT_CALL(mockServer_, Query, 3); return realDb_.Query(); } private: // in non-INTEGRATION_TESTS builds, Server is a mock Server with // extra testing methods that allows mocking Server mockServer_; Database realDb_; }; #endif template <class T> class TestDatabaseContainer { public: int Query(const char* expression) { int result = database_.Query(expression); std::cout << "LOG: " << result << endl; return result; } private: T database_; }; Edit: Note the fake Database must call the real Database (but with a mock Server). Now to switch between them I'm planning the following test framework: class DatabaseTests { public: #ifdef INTEGRATION_TESTS typedef TestDatabaseContainer<Database> TestDatabase ; #else typedef TestDatabaseContainer<FakeDatabase> TestDatabase ; #endif TestDatabase& GetDb() { return _testDatabase; } private: TestDatabase _testDatabase; }; class QueryTestCase : public DatabaseTests { public: void TestStep1() { ASSERT(GetDb().Query(static_cast<const char *>("")) == 3); return; } }; I'm not a big fan of that compile-time switching between the real and the fake. So, my question is: Whether there's a better way of switching between Database and FakeDatabase? For instance, is it possible to do it at runtime in a clean fashion? I like to avoid #ifdefs. Also, if anyone has a better way of making a fake class that mimics a concrete class, I'd appreciate it. I don't want to have templated code all over the actual test code (QueryTestCase class). Feel free to critique the code style itself, too. You can see a compiled version of this code on codepad.

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  • Overwrite values when using gridview Edit?

    - by sah302
    I am using a GridView which is bound to a LinqDataSource and using the automatic edit and delete buttons. However, I don't want the user to edit two of the columns manually, but done automatically. Specifically username who last updated the entry, and the date it was updated. The gridview only contains 3 columns: Name, Date modified, last updated by. Right now when the user clicks the edit button they can only edit the name column (other two set to read-only). Upon clicking the update button, I want the other 2 fields to update as well based on some extra code. I thought this was done in the code behind within the event rowUpdating, but it doesn't seem to work. My gridview: <asp:GridView ID="gvNewsSources" runat="server" AutoGenerateColumns="False" DataSourceID="ldsNewsSource" AutoGenerateDeleteButton="True" AutoGenerateEditButton="True" CellPadding="4" ForeColor="#333333" GridLines="None" DataKeyNames="Id"> <RowStyle BackColor="#F7F6F3" ForeColor="#333333" /> <Columns> <asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name" /> <asp:BoundField DataField="LastUpdatedBy" HeaderText="Last Updated By" SortExpression="LastUpdatedBy" ReadOnly="True" /> <asp:BoundField DataField="DatedModified" HeaderText="Dated Modified" SortExpression="DatedModified" ReadOnly="True" /> </Columns> <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" /> <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" /> <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" /> <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" /> <EditRowStyle BackColor="#999999" /> <AlternatingRowStyle BackColor="White" ForeColor="#284775" /> </asp:GridView> My code behind: Partial Class _Default Inherits System.Web.UI.Page Protected Sub gvNewsSources_RowUpdating(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewUpdateEventArgs) Handles gvNewsSources.RowUpdating e.NewValues("LastUpdatedBy") = GetUser.GetUserName e.NewValues("DateModified") = Date.Now() lblOutput.Text = e.NewValues("DateModified").ToString() End Sub End Class Yet when I run through this, I get no errors, but the values aren't being updated in the database or in the gridview. I ran through debug mode and the new values dictionary starts at 1 and ends up being 3 by the end of the rowUpdating event and the value is being set (tested by output the newValue of Datemodified), but it isn't saving. What am I doing wrong?

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  • User created Validator wont call Client side validation Javascript on 'complex' user control.

    Hi All, I have created a user control (from System.Web.UI.UserControl), and created my own validator for the user control (from System.Web.UI.WebControls.BaseValidator). Everything works ok until I try to get the user control to do client side validation. While trying to debug this issue I have set 'Control to Validate' to a text box instead of the custom user control, and the client side script works fine! It appears to me that it has an a issue with my composite user control I have created. Has anyone encountered this issue before? Has anyone else seen client side validation fail on custom user controls? Some extra info : The composite control is a drop down list and 'loader image', as it is a ajax enabled drop down list (using ICallbackEventHandler). I know that the client side javascript is being written to the page, and have placed an alert('random message') as the first line in the validator function that only appears if it is validating a text box (i.e. not when it is validating my custom control) Language : C# (ASP.NET 2.0) and jQuery 1.2.6 in aspx file : <rms:UserDDL ID="ddlUserTypes" runat="server" PreLoad="true" /> <rms:DDLValidator ID="userTypesVal" ControlToValidate="ddlUserTypes" ErrorMessage="You have not selected a UserType" runat="server" Text="You have not selected a UserType" Display="Dynamic" EnableClientScript="true" /> in validator code behind protected string ScriptBlock { get { string nl = System.Environment.NewLine; return "<script type=\"text/javascript\">" + nl + " function " + ScriptBlockFunctionName + "(ctrl)" + nl + " {" + nl + " alert('Random message'); " + nl + " var selVal = $('#' + ctrl.controltovalidate).val(); " + nl + " alert(selVal);" + nl + " if (selVal === '-1') return false; " + nl + " return false; " + nl + " }" + nl + "</script>"; } } protected override void OnPreRender(EventArgs e) { if (this.DetermineRenderUplevel() && this.EnableClientScript) { Page.ClientScript.RegisterExpandoAttribute(this.ClientID, "evaluationfunction", this.ScriptBlockFunctionName); Page.ClientScript.RegisterClientScriptBlock(GetType(), this.ScriptBlockKey, this.ScriptBlock); } base.OnPreRender(e); } I know my ControlPropertiesValid() and EvaluateIsValid() work ok. I appreciate any help on this issue. Noel.

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  • Can I call make runtime decided method calls in Java?

    - by Catalin Marin
    I know there is an invoke function that does the stuff, I am overall interested in the "correctness" of using such a behavior. My issue is this: I have a Service Object witch contains methods which I consider services. What I want to do is alter the behavior of those services without later intrusion. For example: class MyService { public ServiceResponse ServeMeDonuts() { do stuff... return new ServiceResponse(); } after 2 months I find out that I need to offer the same service to a new client app and I also need to do certain extra stuff like setting a flag, or make or updating certain data, or encode the response differently. What I can do is pop it up and throw down some IFs. In my opinion this is not good as it means interaction with tested code and may result in un wanted behaviour for the previous service clients. So I come and add something to my registry telling the system that the "NewClient" has a different behavior. So I'll do something like this: public interface Behavior { public void preExecute(); public void postExecute(); } public class BehaviorOfMyService implements Behavior{ String method; String clientType; public void BehaviorOfMyService(String method,String clientType) { this.method = method; this.clientType = clientType; } public void preExecute() { Method preCall = this.getClass().getMethod("pre" + this.method + this.clientType); if(preCall != null) { return preCall.invoke(); } return false; } ...same for postExecute(); public void preServeMeDonutsNewClient() { do the stuff... } } when the system will do something like this if(registrySaysThereIs different behavior set for this ServiceObject) { Class toBeCalled = Class.forName("BehaviorOf" + usedServiceObjectName); Object instance = toBeCalled.getConstructor().newInstance(method,client); instance.preExecute(); ....call the service... instance.postExecute(); .... } I am not particularly interested in correctness of code as in correctness of thinking and approach. Actually I have to do this in PHP, witch I see as a kind of Pop music of programming which I have to "sing" for commercial reasons, even though I play POP I really want to sing by the book, so putting aside my more or less inspired analogy I really want to know your opinion on this matter for it's practical necessity and technical approach. Thanks

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  • How to put a background image on GridBagLayout

    - by Loligans
    I am trying to work with layout managers for the first time, and they are just kicking me in the teeth. I am trying to make a background image and then put buttons on top, using GridBagLayout, if there is a a better layoutmanager please do tell. As for trying to learn how to use layout managers, its very difficult and any learning references would also be much appreciated. This is what it looks like currently, I can get the frame to show the full image, but when i use gridlayout manager, it does that public void addComponentsToPane(Container pane){ BackgroundImage image = new BackgroundImage(); JButton button1, button2, button3, button4, button5; pane.setLayout(new GridBagLayout()); GridBagConstraints c = new GridBagConstraints(); if(shouldFill){ c.fill = GridBagConstraints.NONE; } button1 = new JButton("Button 1"); if (shouldWeightX) { c.weightx = 0.5; } c.fill = GridBagConstraints.HORIZONTAL; c.gridx = 1; c.gridy = 0; button1.setOpaque(false); pane.add(button1, c); button2 = new JButton("Button 2"); c.fill = GridBagConstraints.HORIZONTAL; c.weightx = 0.5; c.gridx = 0; c.gridy = 0; button2.setOpaque(false); pane.add(button2, c); button3 = new JButton("Button 3"); c.fill = GridBagConstraints.HORIZONTAL; c.weightx = 0.5; c.gridx = 2; c.gridy = 0; button3.setOpaque(false); pane.add(button3, c); button4 = new JButton("Long-Named Button 4"); c.fill = GridBagConstraints.HORIZONTAL; c.ipady = 40; //make this component tall c.weightx = 0.0; c.gridwidth = 3; c.gridx = 0; c.gridy = 1; pane.add(button4, c); button5 = new JButton("button 1"); c.fill = GridBagConstraints.HORIZONTAL; c.ipady = 0; //reset to default c.weighty = 1.0; //request any extra vertical space c.anchor = GridBagConstraints.PAGE_END; //bottom of space c.insets = new Insets(10,0,0,0); //top padding c.gridx = 1; //aligned with button 2 c.gridwidth = 2; //2 columns wide c.gridy = 2; //third row pane.add(button5, c); c.ipadx = 800; c.ipady = 400; pane.add(image, c); } This is what i'm trying to make it look like

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  • Optimize MySQL query (ngrams, COUNT(), GROUP BY, ORDER BY)

    - by Gerardo
    I have a database with thousands of companies and their locations. I have implemented n-grams to optimize search. I am making one query to retrieve all the companies that match with the search query and another one to get a list with their locations and the number of companies in each location. The query I am trying to optimize is the latter. Maybe the problem is this: Every company ('anunciante') has a field ('estado') to make logical deletes. So, if 'estado' equals 1, the company should be retrieved. When I run the EXPLAIN command, it shows that it goes through almost 40k rows, when the actual result (the reality matching companies) are 80. How can I optimize this? This is my query (XXX represent the n-grams for the search query): SELECT provincias.provincia AS provincia, provincias.id, COUNT(*) AS cantidad FROM anunciantes JOIN anunciante_invertido AS a_i0 ON anunciantes.id = a_i0.id_anunciante JOIN indice_invertido AS indice0 ON a_i0.id_invertido = indice0.id LEFT OUTER JOIN domicilios ON anunciantes.id = domicilios.id_anunciante LEFT OUTER JOIN localidades ON domicilios.id_localidad = localidades.id LEFT OUTER JOIN provincias ON provincias.id = localidades.id_provincia WHERE anunciantes.estado = 1 AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') GROUP BY provincias.id ORDER BY cantidad DESC And this is the query explained (hope it can be read in this format): id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY anunciantes ref PRIMARY,estado estado 1 const 36669 Using index; Using temporary; Using filesort 1 PRIMARY domicilios ref id_anunciante id_anunciante 4 db84771_viaempresas.anunciantes.id 1 1 PRIMARY localidades eq_ref PRIMARY PRIMARY 4 db84771_viaempresas.domicilios.id_localidad 1 1 PRIMARY provincias eq_ref PRIMARY PRIMARY 4 db84771_viaempresas.localidades.id_provincia 1 1 PRIMARY a_i0 ref PRIMARY,id_anunciante,id_invertido PRIMARY 4 db84771_viaempresas.anunciantes.id 1 Using where; Using index 1 PRIMARY indice0 eq_ref PRIMARY PRIMARY 4 db84771_viaempresas.a_i0.id_invertido 1 Using index 6 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 6 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 5 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 5 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 4 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 4 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 3 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 3 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 2 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 2 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index

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  • File sizing issue in DOS/FAT

    - by Heather
    I've been tasked with writing a data collection program for a Unitech HT630, which runs a proprietary DOS operating system that can run executables compiled for 16-bit MS DOS with some restrictions. I'm using the Digital Mars C/C++ compiler, which is working well thus far. One of the application requirements is that the data file must be human-readable plain text, meaning the file can be imported into Excel or opened by Notepad. I'm using a variable length record format much like CSV that I've successfully implemented using the C standard library file I/O functions. When saving a record, I have to calculate whether the updated record is larger or smaller than the version of the record currently in the data file. If larger, I first shift all records immediately after the current record forward by the size difference calculated before saving the updated record. EOF is extended automatically by the OS to accommodate the extra data. If smaller, I shift all records backwards by my calculated offset. This is working well, however I have found no way to modify the EOF marker or file size to ignore the data after the end of the last record. Most of the time records will grow in size because the data collection program will be filling some of the empty fields with data when saving a record. Records will only shrink in size when a correction is made on an existing entry, or on a normal record save if the descriptive data in the record is longer than what the program reads in memory. In the situation of a shrinking record, after the last record in the file I'm left with whatever data was sitting there before the shift. I have been writing an EOF delimiter into the file after a "shrinking record save" to signal where the end of my records are and space-filling the remaining data, but then I no longer have a clean file until a "growing record save" extends the size of the file over the space-filled area. The truncate() function in unistd.h does not work (I'm now thinking this is for *nix flavors only?). One proposed solution I've seen involves creating a second file and writing all the data you wish to save into that file, and then deleting the original. Since I only have 4MB worth of disk space to use, this works if the file size is less than 2MB minus the size of my program executable and configuration files, but would fail otherwise. It is very likely that when this goes into production, users would end up with a file exceeding 2MB in size. I've looked at Ralph Brown's Interrupt List and the interrupt reference in IBM PC Assembly Language and Programming and I can't seem to find anything to update the file size or similar. Is reducing a file's size without creating a second file even possible in DOS?

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  • Trying to style the first tbody different than others without introducing another class.

    - by mwiik
    I have a table with multiple tbody's, each of which has a classed row, and I want it so that the classed row in the first tbody has style differences, but am unable to get tbody:first-child to work in any browser. Perhaps I am missing something, or maybe there is a workaround. Ideally, I would like to provide the programmers with a single tbody section they can use as a template, but will otherwise have to add a class to the first tbody, making for an extra test in the programming. The html is straightforward: <tbody class="subGroup"> <tr class="subGroupHeader"> <th colspan="8">All Grades: Special Education</th> <td class="grid" colspan="2"><!-- contains AMO line --></td> <td><!-- right 100 --></td> </tr> <tr>...</tr> <!-- several more rows of data --> </tbody> There are several tbody's per table. I want to style the th and td's within tr.subGroupHeader in the very first tbody differently than the rest. Just to illustrate, I want to add a border-top to the tr.subGroupHeader cells. The tr.subGroupHeader will be styled with a border-top, such as: table.databargraph.continued tr.subGroupHeader th, table.databargraph.continued tr.subGroupHeader td { border-top: 6px solid red; } For the first tbody, I am trying: table.databargraph.continued tbody:first-child tr.subGroupHeader th { border-top: 6px solid blue ; } However, this doesn't seem to work in any browser (I've tested in Safari, Opera, Firefox, and PrinceXML, all on my Mac) Curiously, the usually excellent Xyle Scope tool indicates that the blue border should be taking precedence, though it obviously is not. See the screenshot at http://s3.amazonaws.com/ember/kUD8DHrz06xowTBK3qpB2biPJrLWTZCP_o.png This screenshot shows (top left) the American Indian th is selected, and (bottom right), shows (via black instead of gray text for the css declaration), that, indeed, the blue border should be given precedence. Yet the border is red. I may be missing something fundamental, like pseudo-classes not working for tbodys at all... This really only needs to work in PrinceXML, and maybe Safari so I can see what I'm doing with webkit-based css tools. Note I did try a selector like tr.subGroupHeader:first-child, but such tr's apparently consider the tbody the parent (as I would suspect), thus made every border blue. Thanks...

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  • Who calls the Destructor of the class when operator delete is used in multiple inheritance.

    - by dicaprio-leonard
    This question may sound too silly, however , I don't find concrete answer any where else. With little knowledge on how late binding works and virtual keyword used in inheritance. As in the code sample, when in case of inheritance where a base class pointer pointing to a derived class object created on heap and delete operator is used to deallocate the memory , the destructor of the of the derived and base will be called in order only when the base destructor is declared virtual function. Now my question is : 1) When the destructor of base is not virtual, why the problem of not calling derived dtor occur only when in case of using "delete" operator , why not in the case given below: derived drvd; base *bPtr; bPtr = &drvd; //DTOR called in proper order when goes out of scope. 2) When "delete" operator is used, who is reponsible to call the destructor of the class? The operator delete will have an implementation to call the DTOR ? or complier writes some extra stuff ? If the operator has the implementation then how does it looks like , [I need sample code how this would have been implemented]. 3) If virtual keyword is used in this example, how does operator delete now know which DTOR to call? Fundamentaly i want to know who calls the dtor of the class when delete is used. Sample Code class base { public: base() { cout<<"Base CTOR called"<<endl; } virtual ~base() { cout<<"Base DTOR called"<<endl; } }; class derived:public base { public: derived() { cout<<"Derived CTOR called"<<endl; } ~derived() { cout<<"Derived DTOR called"<<endl; } }; I'm not sure if this is a duplicate, I couldn't find in search. int main() { base *bPtr = new derived(); delete bPtr;// only when you explicitly try to delete an object return 0; }

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