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  • Does the usage of interfaces slow down programs?

    - by Olga
    Is it true that interfaces slow down programs? I have heard that this is the case because during running time each during each usage of an object implementing this interface the decision has to be made which class implementing the interface this object belongs to. I am especially interested in an answer for C++, but also in general. And if this is true, some numbers would be helpful, too. Thank you very much!

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  • Binding on a port with netpipes/netcat

    - by mindas
    I am trying to write a simple bash script that is listening on a port and responding with a trivial HTTP response. My specific issue is that I am not sure if the port is available and in case of bind failure I fall back to next port until bind succeeds. So far to me the easiest way to achieve this was something like: for (( i=$PORT_BASE; i < $(($PORT_BASE+$PORT_RANGE)); i++ )) do if [ $DEBUG -eq 1 ] ; then echo trying to bind on $i fi /usr/bin/faucet $i --out --daemon echo test 2>/dev/null if [ $? -eq 0 ] ; then #success? port=$i if [ $DEBUG -eq 1 ] ; then echo "bound on port $port" fi break fi done Here I am using faucet from netpipes Ubuntu package. The problem with this is that if I simply print "test" to the output, curl complains about non-standard HTTP response (error code 18). That's fair enough as I don't print HTTP-compatible response. If I replace echo test with echo -ne "HTTP/1.0 200 OK\r\n\r\ntest", curl still complains: user@server:$ faucet 10020 --out --daemon echo -ne "HTTP/1.0 200 OK\r\n\r\ntest" ... user@client:$ curl ip.of.the.server:10020 curl: (56) Failure when receiving data from the peer I think the problem lies in how faucet is printing the response and handling the connection. For example if I do the server side in netcat, curl works fine: user@server:$ echo -ne "HTTP/1.0 200 OK\r\n\r\ntest\r\n" | nc -l 10020 ... user@client:$ curl ip.of.the.server:10020 test user@client:$ I would be more than happy to replace faucet with netcat in my main script, but the problem is that I want to spawn independent server process to be able to run client from the same base shell. faucet has a very handy --daemon parameter as it forks to background and I can use $? (exit status code) to check if bind succeeded. If I was to use netcat for a similar purpose, I would have to fork it using & and $? would not work. Does anybody know why faucet isn't responding correctly in this particular case and/or can suggest a solution to this problem. I am not married neither to faucet nor netcat but would like the solution to be implemented using bash or it's utilities (as opposed to write something in yet another scripting language, such as Perl or Python).

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  • Spinning a circle in J2ME using a Canvas.

    - by JohnQPublic
    Hello all! I have a problem where I need to make a multi-colored wheel spin using a Canvas in J2ME. What I need to do is have the user increase the speed of the spin or slow the spin of the wheel. I have it mostly worked out (I think) but can't think of a way for the wheel to spin without causing my cellphone to crash. Here is what I have so far, it's close but not exactly what I need. class MyCanvas extends Canvas{ //wedgeOne/Two/Three define where this particular section of circle begins to be drawn from int wedgeOne; int wedgeTwo; int wedgeThree; int spinSpeed; MyCanvas(){ wedgeOne = 0; wedgeTwo = 120; wedgeThree = 240; spinSpeed = 0; } //Using the paint method to public void paint(Graphics g){ //Redraw the circle with the current wedge series. g.setColor(255,0,0); g.fillArc(getWidth()/2, getHeight()/2, 100, 100, wedgeOne, 120); g.setColor(0,255,0); g.fillArc(getWidth()/2, getHeight()/2, 100, 100, wedgeTwo, 120); g.setColor(0,0,255); g.fillArc(getWidth()/2, getHeight()/2, 100, 100, wedgeThree, 120); } protected void keyPressed(int keyCode){ switch (keyCode){ //When the 6 button is pressed, the wheel spins forward 5 degrees. case KEY_NUM6: wedgeOne += 5; wedgeTwo += 5; wedgeThree += 5; repaint(); break; //When the 4 button is pressed, the wheel spins backwards 5 degrees. case KEY_NUM4: wedgeOne -= 5; wedgeTwo -= 5; wedgeThree -= 5; repaint(); } } I have tried using a redraw() method that adds the spinSpeed to each of the wedge values while(spinSpeed0) and calls the repaint() method after the addition, but it causes a crash and lockup (I assume due to an infinite loop). Does anyone have any tips or ideas how I could automate the spin so you do not have the press the button every time you want it to spin? (P.S - I have been lurking for a while, but this is my first post. If it's too general or asking for too much info (sorry if it is) and I either remove it or fix it. Thank you!)

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  • what should be the return type of the hashCode()

    - by subhashis
    The signature of the hashCode() method is public int hashCode(){ return x; } in this case x must be an int(primitive) but plz can anyone explain it to me that the number which the hashCode() returns must be a prime number, even number...etc or there is no specification ? the reason behind i am asking this question is i have seen it in different ids the auto generated code always returns a prime number, so i need to know why? thanks in advance

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  • Update Params in Python During Infinite Loop

    - by python Dude
    Hello, I was hoping to get some help on a question. I have an infinite loop that I need run and I need to update a set of variables (x in this case) at random times from the command-line. Is there any way to do this? For example: x = 0 while True: x = x + 1 if x < 30: do something and I need to update x's value from the command-line periodically

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  • how does sql count work?

    - by ria
    I would like to understand how exactly does sql count work. Is it a whole table scan that happens or is it some property of the table that is read. However I feel a table scan would be an overhead in case of huge tables with lots of records.

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  • Is there a better way to declare an empty, typed matrix in MATLAB?

    - by Arthur Ward
    Is there a way to "declare" a variable with a particular user-defined type in MATLAB? zeros() only works for built-in numeric types. The only solution I've come up with involves using repmat() to duplicate a dummy object zero times: arr = repmat(myClass(), [1 0]) Without declaring variables this way, any code which does "arr(end+1) = myClass()" has to include a special case for the default empty matrix which is of type double. Have I missed something a little more sensible?

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  • How do "and" and "or" work when combined in one statement?

    - by orokusaki
    For some reason this function confused me: def protocol(port): return port == "443" and "https://" or "http://" Can somebody explain the order of what's happening behind the scenes to make this work the way it does. I understood it as this until I tried it: Either A) def protocol(port): if port == "443": if bool("https://"): return True elif bool("http://"): return True return False Or B) def protocol(port): if port == "443": return True + "https://" else: return True + "http://" Is this some sort of special case in Python, or am I completely misunderstanding how statements work?

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  • "this" in function parameter

    - by chris
    Looking at some code examples for HtmlHelpers, and I see declarations that look like: public static string HelperName(this HtmlHelper htmlHelper, ...more regular params ) I can't remember seeing this type of construct any where else - can someone explain the purpose of the "this"? I thought that by declaring something public static meant that the class did not need to be instantiated - so what is "this" in this case?

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  • Why Windows Live Spaces Fetch Image Through HTTPS?

    - by Morgan Cheng
    I happens to find that, when a live space page is loaded, inline images are fetched by https protocol instead of http protocol. This doesn't make sense. The text part of live space is not fetched by https, why images are fetched with https? I bet the https way to fetch image just make the page loaded slower. Is there any special advantage to choose https over http in this case?

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  • how to tell which object called a delegate method (objective c)

    - by user353877
    Let's say you have two objects (UITextviews) in your class. When the text view changes, you have a delegate method that catches the change.. but how can you tell programatically WHICH object was changed and called the delegate ?? I have to be missing something, because this should be trivial, but I couldnt find anything. Note: In this case, its not possible to just break up the class to only have one object (there by bypassing ambiguity).. I looked for things like assigned variable names for nsobjects, nothing there

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  • Which network protocol to use for lightweight notification of remote apps (Delphi 2005)

    - by Chris Thornton
    I have this situation.... Client-initiated SOAP 1.1 communication between one server and let's say, tens of thousands of clients. Clients are external, coming in through our firewall, authenticated by certificate, https, etc.. They can be anywhere, and usually have their own firewalls, NAT routers, etc... They're truely external, not just remote corporate offices. They could be in a corporate/campus network, DSL/Cable, even Dialup. Currently, clients push new data to the server and pull new data from the server on 15-minute polling loop. The server currently does not push data - the client hits the "messagecount" method, to see if there is new data to pull. If 0, it sleeps for another 15 min and checks again. We're trying to get that down to 7 seconds. If this were an internal app, with one or just a few dozen clients, we'd write a cilent "listener" soap service, and would push data to it. But since they're external, sit behind their own firewalls, and sometimes private networks behind NAT routers, this is not practical. So we're left with polling on a much quicker loop. 10K clients, each checking their messagecount every 10 seconds, is going to be 1000/sec messages that will mostly just waste bandwidth, server, firewall, and authenticator resources. So I'm trying to design something better than what would amount to a self-inflicted DoS attack. I don't think it's practical to have the server send soap messages to the client (push) as this would require too much configuration at the client end. But I think there are alternatives that I don't know about. Such as: 1) Is there a way for the client to make a request for GetMessageCount() via Soap 1.1, and get the response, and then perhaps, "stay on the line" for perhaps 5-10 minutes to get additional responses in case new data arrives? i.e the server says "0", then a minute later in response to some SQL trigger (the server is C# on Sql Server, btw), knows that this client is still "on the line" and sends the updated message count of "5"? 2) Is there some other protocol that we could use to "ping" the client, using information gathered from their last GetMessageCount() request? 3) I don't even know. I guess I'm looking for some magic protocol where the client can send a GetMessageCount() request, which would include info for "oh by the way, in case the answer changes in the next hour, ping me at this address...". Also, I'm assuming that any of these "keep the line open" schemes would seriously impact the server sizing, as it would need to keep many thousands of connections open, simultaneously. That would likely impact the firewalls too, I think. Is there anything out there like that? Or am I pretty much stuck with polling? TIA, Chris

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  • How to get the name of the method that caused the exception

    - by SKumar
    My code looks as below. try { _productRepo.GetAllProductCategories(); } catch (Exception ex) { //Do Something } I need a way to show the method name, suppose in the above case if any exception is thrown in the GetAllProductCategories() method, I need to get this method name i.e. "GetAllProductCategories()" as my result. Can any one suggest me how to do this?

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  • how to invoke an activity of a library project from an android apps

    - by Austin
    I have an open source android code that I need to use in my android apps. It has all the source code as well as resource files, manifest files and class path. It can be compiled as a separate android apps. I have constraints for using the open source. 1. I can't change a single line of code. 2. I can't use it as a separate apps. These constraints are non negotiable. What I have done is I have compiled the open source as class library(in Eclipse: Project Properties-Android- Tick check box Is Library). This has resulted in generation of .class files(in bin) for the java files and resource files. This open source has an android activity that i want to open from my application. So I have linked the directory of these sets of class files in the source section of my java build path( in .classpath). I have declared the activity in my manifest file with proper action intent filters. Now when I am trying to call activity from my code, its not working. Cleaning and rebuilding doesn't help. However, if I build the open source project and my apps in the same workspace of eclipse and link the open source in my apps in exact same manner it works fine. I am not able to identify the difference. All settings seems to be same(all files are identical in both the cases). But only in the second case it works. I have tried it as jar file also. I have build the open source as project library and exported it into a jar file(excluding manifest file). But in that case I am getting the following error UNEXPECTED TOP-LEVEL EXCEPTION: java.lang.IllegalArgumentException: already added: .... Conversion to Dalvik format failed with error 1 This I guess is coming because the android library(2.2) has been included twice in my apps( one for building my apps & another for building the open source). I dont know how to avoid this. Cleaning the project doesn't help. What i require is to use the open source and invoking it's activities in my apps without violating the constraints. If i can use the open source as bunch of .class files then great, or else any other way will do fine. Please look into it and let me know. Thanks

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  • Application self aware of external database record modifications.

    - by Khou
    How do you make your application aware that a database record was changed or created by an external application rather than the application itself? Do you add a special check sum to the database record or what do you do to stop external changes to the database? (in case it was hacked and the hacker decides to add a new record or change an existing database record)

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  • MySQL- complex data query in a single statement

    - by yoda
    Hi, Consider the following structure : Ignore the table user_token. Now, imagine that you need to get all the roles related to an user, wich may be through it's related groups or directly related to him. In case the same role appears related to a group and the user directly, the role related to the user will prevail over the role given by the group. Is there any chance this could be done in a single query? Cheers!

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  • Remove all user's cookies/sessions when password is reset

    - by Juraj
    I'm interested in improving security of my TurboGears 2.2 application so that when user changes his password, it logs him out from all sessions and he must login again. When user changes password on browser 1, he must relogin on browser 2, too. Experiments show that this is not the case, especially if browser 2 had "remember me" enabled. It's standard quickstarted app using repoze.who. It seems maybe I need to change AuthTktCookiePlugin, but don't see a way to do it without much rewiring.

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