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• Size of abstract class

  - by webgenius

  How can I find the size of an abstract class? class A { virtual void PureVirtualFunction() = 0; }; Since this is an abstract class, I can't create objects of this class. How will I be able to find the size of the abstract class A using the 'sizeof' operator?

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• Is there any g++ option to dump class layout and vtables?

  - by Aman Jain

  Hi I want to see how g++ lays out memory for classes and virtual tables. Is there a way to do it? Thanks

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• Linux iptables / conntrack performance issue

  - by tim

  I have a test-setup in the lab with 4 machines: 2 old P4 machines (t1, t2) 1 Xeon 5420 DP 2.5 GHz 8 GB RAM (t3) Intel e1000 1 Xeon 5420 DP 2.5 GHz 8 GB RAM (t4) Intel e1000 to test linux firewall performance since we got bitten by a number of syn-flood attacks in the last months. All machines run Ubuntu 12.04 64bit. t1, t2, t3 are interconnected through an 1GB/s switch, t4 is connected to t3 via an extra interface. So t3 simulates the firewall, t4 is the target, t1,t2 play the attackers generating a packetstorm thorugh (192.168.4.199 is t4): hping3 -I eth1 --rand-source --syn --flood 192.168.4.199 -p 80 t4 drops all incoming packets to avoid confusion with gateways, performance issues of t4 etc. I watch the packet stats in iptraf. I have configured the firewall (t3) as follows: stock 3.2.0-31-generic #50-Ubuntu SMP kernel rhash_entries=33554432 as kernel parameter sysctl as follows: net.ipv4.ip_forward = 1 net.ipv4.route.gc_elasticity = 2 net.ipv4.route.gc_timeout = 1 net.ipv4.route.gc_interval = 5 net.ipv4.route.gc_min_interval_ms = 500 net.ipv4.route.gc_thresh = 2000000 net.ipv4.route.max_size = 20000000 (I have tweaked a lot to keep t3 running when t1+t2 are sending as many packets as possible). The result of this efforts are somewhat odd: t1+t2 manage to send each about 200k packets/s. t4 in the best case sees aroung 200k in total so half of the packets are lost. t3 is nearly unusable on console though packets are flowing through it (high numbers of soft-irqs) the route cache garbage collector is no way near to being predictable and in the default setting overwhelmed by very few packets/s (<50k packets/s) activating stateful iptables rules makes the packet rate arriving on t4 drop to around 100k packets/s, efectively losing more than 75% of the packets And this - here is my main concern - with two old P4 machines sending as many packets as they can - which means nearly everyone on the net should be capable of this. So here goes my question: Did I overlook some importand point in the config or in my test setup? Are there any alternatives for building firewall system especially on smp systems?

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• How to infer the type of a derived class in base class?

  - by enzi

  I want to create a method that allows me to change arbitrary properties of classes that derive from my base class, the result should look like this: SetPropertyValue("size.height", 50); – where size is a property of my derived class and height is a property of size. I'm almost done with my implementation but there's one final obstacle that I want to solve before moving on, to describe this I will first have to explain my implementation a bit: Properties that can be modified are decorated with an attribute There's a method in my base class that searches for all derived classes and their decorated properties For each property I generate a "property modifier", a class that contains 2 delegates: one to set and one to get the value of the property. Property Modifiers are stored in a dictionary, with the name of the property as key In my base class, there is another dictionary that contains all property-modifier-dictionaries, with the Type of the respective class as key. What the SetPropertyValue method does is this: Get the correct property-modifier-dictionary, using the concrete type of the derived class (<- yet to solve) Get the property modifier of the property to change (e.g. of the property size) Use the get or set delegate to modify the property's value Some example code to clarify further: private static Dictionary<RuntimeTypeHandle, object> EditableTypes; //property-modifier-dictionary protected void SetPropertyValue<T>(EditablePropertyMap<T> map, string property, object value) { var property = map[property]; // get the property modifier property.Set((T)this, value); // use the set delegate (encapsulated in a method) } In the above code, T is the Type of the actual (derived) class. I need this type for the get/set delegates. The problem is how to get the EditablePropertyMap<T> when I don't know what T is. My current (ugly) solution is to pass the map in an overriden virtual method in the derived class: public override void SetPropertyValue(string property, object value) { base.SetPropertyValue((EditablePropertyMap<ExampleType>)EditableTypes[typeof(ExampleType)], property, value); } What this does is: get the correct dictionary containing the property modifiers of this class using the class's type, cast it to the appropiate type and pass it to the SetPropertyValue method. I want to get rid of the SetPropertyValue method in my derived class (since there are a lot of derived classes), but don't know yet how to accomplish that. I cannot just make a virtual GetEditablePropertyMap<T> method because I cannot infer a concrete type for T then. I also cannot acces my dictionary directly with a type and retrieve an EditablePropertyMap<T> from it because I cannot cast to it from object in the base class, since again I do not know T. I found some neat tricks to infere types (e.g. by adding a dummy T parameter), but cannot apply them to my specific problem. I'd highly appreciate any suggestions you may have for me.

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• showing content from subdomain

  - by coure06

  I have a root site in httpdocs folder. There is another website (for subdomain) at httpdocs/demo1 Mapping is like www.abc.com to httpdocs demo1.abco.com to httpdocs/demo1 How can I show image from demo1 folder? I want to access it like www.abc.com/demo1/images/some.png Error: Parser Error Message: It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS.

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• Windows 7 x64 support for Intel GMA 3650 (or GMA 3600)

  - by Loom

  I recently purchased an Intel D2700 MUD motherboard and I cannot find drivers for the Win7 x64 integrated graphics (Intel GMA 3650 aka PowerVR sgs545). The accompanying CD contains Win7 x32 version only. When I run it I got an error: This computer does not meet the minimum requirements for installing the software. I tried to use online utility Intel Driver Update Utility Graphics. I used Chrome, Firefox, Internet Explorer without success. First, UAC prompt appear, and then endlessly spinning progress-bar with text "Analyzing computer...". The text in UAC prompt is: Program file name: System Requirements Lab Verified publisher: Husdawg, LLC I downloaded this utility (intel_srldetect_4.5.5.0) and started it from my hard disk. I got an error: A network error occured while attempting to read from the file: C:\Users\Loom\Downloads\SystemRequirementsLab_intel_4.5.5.0.msi Standard VGA driver works for this video card but without hardware acceleration: Hardware acceleration is either disabled or not supported by your video card driver, which could slow game performance. Make sure you have the latest video card driver installed and that hardware acceleration is turned on. Where I can get appropriate driver?

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• What classes should I map against with NHibernate?

  - by apollodude217

  Currently, we use NHibernate to map business objects to database tables. Said business objects enforce business rules: The set accessors will throw an exception on the spot if the contract for that property is violated. Also, the properties enforce relationships with other objects (sometimes bidirectional!). Well, whenever NHibernate loads an object from the database (e.g. when ISession.Get(id) is called), the set accessors of the mapped properties are used to put the data into the object. What's good is that the middle tier of the application enforces business logic. What's bad is that the database does not. Sometimes crap finds its way into the database. If crap is loaded into the application, it bails (throws an exception). Sometimes it clearly should bail because it cannot do anything, but what if it can continue working? E.g., an admin tool that gathers real-time reports runs a high risk of failing unnecessarily instead of allowing an admin to even fix a (potential) problem. I don't have an example on me right now, but in some instances, letting NHibernate use the "front door" properties that also enforce relationships (especially bidi) leads to bugs. What are the best solutions? Currently, I will, on a per-property basis, create a "back door" just for NHibernate: public virtual int Blah {get {return _Blah;} set {/*enforces BR's*/}} protected virtual int _Blah {get {return blah;} set {blah = value;}} private int blah; I showed the above in C# 2 (no default properties) to demonstrate how this gets us basically 3 layers of, or views, to blah!!! While this certainly works, it does not seem ideal as it requires the BL to provide one (public) interface for the app-at-large, and another (protected) interface for the data access layer. There is an additional problem: To my knowledge, NHibernate does not give you a way to distinguish between the name of the property in the BL and the name of the property in the entity model (i.e. the name you use when you query, e.g. via HQL--whenever you give NHibernate the name (string) of a property). This becomes a problem when, at first, the BR's for some property Blah are no problem, so you refer to it in your O/R mapping... but then later, you have to add some BR's that do become a problem, so then you have to change your O/R mapping to use a new _Blah property, which breaks all existing queries using "Blah" (common problem with programming against strings). Has anyone solved these problems?!

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• serialport or USB port?

  - by I__

  i am using this code:: http://stackoverflow.com/questions/3033324/c-serialport-question/3033402#3033402 to check what port my USB phone is connected to. supposedly USB would be a virtual com, but this seems to be incorrect i used the above code to detect where my phone is and the output is just garbage. is there a way for me to get c# to speak to my usb port so that i can speak to the gsm phone connected to it?

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• Access XAMPP Localhost from Internet

  - by coool

  Hi, I have XAMPP installed in local laptop. And I have a almost static ip. I would like to give the ip to other to run it from thier browser. I configured apache httpd-vhosts.conf to listen my ip address:80 and added the virtual server with the ip address and domain root to local httdocs directory and the servername as localhost. Apache doesn't start. what should I do to access my website from external computer. THnks

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• Access specifier while overriding methods

  - by Pradyot

  Assume you have a class that defines virtual methods with the access specifier public. Can you change the access specifier on your overriden methods? I am assuming no. Looking for an explanation.

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• I can't get my Android program to run correctly on an AVM in Eclipse

  - by Wes

  This is a simple question about getting started with developing Android apps using Eclipse. I have followed all the tutorials on the developer site for installing Eclipse, the SDK and the ADT plugin. When trying to run a simple Hello World program, everything seems to compile correctly, but then the virtual machine comes up empty. In the Console Window it reads: The program then just sits and my text never comes up. Any idea with what the problem could be?

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• SQL Server 2008 takes up a lot of memory?

  - by Ahmed Said

  I am conducting stress tests on my database, which is hosted on SQL Server 2008 64-bit running on a 64-bit machine with 10 GB of RAM. I have 400 threads. Each thread queries the database every second, but the query time does not take time, as the SQL profiler says that, but after 18 hours SQL Server uses up 7.2 GB of RAM and 7.2 GB of virtual memory. Is this normal behavior? How can I adjust SQL Server to clean up unused memory?

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• Resources for writing kernel in C

  - by anon

  I don't want to write my own boot loader -- happy to use Grub. I just want to implement pre-emptive multi threading, a basic file system, and virtual memory. I want something that can run on top of qemu. What's a good resource (book / tutorial) for accomplishing this goal? Thanks!

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• Reopening serial port fails if not closed properly with CloseHandle

  - by superg

  I am working with USB device on Windows that is seen as a virtual serial port. I can communicate with the device using CreateFile and ReadFile functions, but in some cases my application does not call CloseHandle (when my application in development crashes). After that all calls to CreateFile fail (ERROR_ACCESS_DENIED), and the only solution is to log in to my computer again. Is there any way to force closing the open handle (or reopening) programmatically?

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• How to test a site rigorously?

  - by Sarfraz

  Hello, I recently created a big portal site. It's time for putting it to test. How do you guys test a site rigorously? What are the ways and tools for that? Can we sort of mimic hundreds of virtual users visiting the site to see its load handling? The test should be for both security and speed Thanks in advance.

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• Determining physical location of data on a disc

  - by Synetech

  Does anybody know of a way to find out where, physically on a CD or DVD a given piece of data would be located? I am trying to watch a DVD at the moment, and am about half-way through, but it keeps dying at a specific spot in the film, presumably because of a scratch. I have a repair kit, but I don’t know where to focus my repair because there are several scuffs and scratches on the disc and I have no way of knowing which one is causing the issue. Obviously, cleaning all of them is inadvisable because not only does it waste the consumable materials in the kit, but not all of them are a problem, and by working them, some may become unreadable. Moreover, just because I am half-way through the movie does not mean that it would be half-way from the hub to the edge for several reasons: Discs have more data towards the outer edge than the inner edge (circles are more mathematically complicated than rectangles) The disc is not completely filled up (and even if it were, the movie itself would be be using it all, there are extras and such) Because in this particular case it is a commercial DVD, it is also dual-layer which further complicates manual determination As such, I am trying to find a program that can let me identify a file (or part thereof), cluster, etc. and show me a picture of where on the CD/DVD it would be located. That way, I can look at the disc and fix any scratches that correspond to that distance from the hub. For example, the image below might indicate where on a disc a couple of files or range of clusters would be located, so by looking for anomalies in those areas (rotating as necessary), the correct one can be identified. I’m sure it can be done since at least one form of copy protection (DPM) uses it and DVD-lab Pro includes a “DVD Topology” feature to do this.

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• Remote offscreen rendering

  - by redmoskito

  My research lab recently added a server that has a beefy NVIDIA graphics card, which we would like to use to do scientific computations. Since it isn't a workstation, we'll have to run our jobs remotely, over an ssh connection. Most of our applications require doing opengl rendering to an offscreen buffer, then doing image analysis on the result in CUDA. My initial investigation suggests that X11 forwarding is a bad idea, because opengl rendering will occur on the client machine (or rather the X11 server--what a confusing naming convention!) and will suffer network bottlenecks when sending our massive textures. We will never need to display the output, so it seems like X11 forwarding shouldn't be necessary, but Opengl needs the $DISPLAY to be set to something valid or our applications won't run. I'm sure render farms exist that do this, but how is it accomplished? I think this is probably a simple X11 configuration issue, but I'm too unfamiliar with it to know where to start. We're running Ubuntu server 10.04, with no gdm, gnome, etc installed. However, xserver-xorg package is installed.

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• writing to an ioport resulting in segfaults...

  - by Sniperchild

  I'm writing for an atmel at91sam9260 arm 9 cored single board computer [glomation gesbc9260] Using request_mem_region(0xFFFFFC00,0x100,"name"); //port range runs from fc00 to fcff that works fine and shows up in /proc/iomem then i try to write to the last bit of the port at fc20 with writel(0x1, 0xFFFFFC20); and i segfault...specifically "unable to handle kernel paging request at virtual address fffffc20. I'm of the mind that i'm not allocating the right memory space... any helpful insight would be great...

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• Graceful way to exit a dm_job ? System.exit()?

  - by Ayrad

  If I want to properly exit a documentum java job (if params are invalid for example), should I use a system.exit() or is there another way to do it. As far as I know system.exit closes the virtual machine, does it have an effect on other jobs running?

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• uploaded image doesn't change in the browser, although on the drive I have the new image

  - by Omu

  I have a View where I can upload an image and the image is also displayed in there like this: //ResourceStorage is a virtual directory that indicates to the pictures storage location <img src='<%=Url.Content("~/ResourceStorage/Profile/pic.jpg") %>' alt='pic' /> after I upload the picture, on the hard drive I get the new "pic.jpg" but in the browser I still have the old one (I tried clearing the cache, doesn't help)

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• C++ code which is slower than its C equivalent?

  - by user997112

  Are there any aspects to the C++ programming language where the code is known to be slower than the equivalent C language? Obviously this would be excluding the OO features like virtual functions and vtable features etc. I am wondering whether, when you are programming in a latency-critical area (and you aren't worried about OO features) whether you could stick with basic C++ or would C be better?

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• RTTI and Portability in C++

  - by Joshua

  If a compiler doesn't "support" RTTI, does that mean that the compiler can not handle class hierarchies that have virtual functions in them? Or have I been misunderstanding the literature about how RTTI isn't portable, and the issues lie elsewhere?

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• No outbound internet connection after restarting CentOS 6.3

  - by wnstnsmth

  After restarting a headless CentOS 6.3 machine, it lost outbound internet connectivity, i.e. I can still connect to the server via SSH (ssh root@**.126.18.56), but stuff such as ping google.com gives google.com: unknown host, and yum list some_package gives a lot of network errors. This is what ifconfig gives: eth0 Link encap:Ethernet HWaddr 00:25:90:78:2D:5D inet addr:**.126.18.56 Bcast:**.126.18.255 Mask:255.255.255.0 inet6 addr: fe80::225:90ff:fe78:2d5d/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:75594 errors:0 dropped:0 overruns:0 frame:0 TX packets:787 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:7074741 (6.7 MiB) TX bytes:144391 (141.0 KiB) Interrupt:20 Memory:f7a00000-f7a20000 eth1 Link encap:Ethernet HWaddr 00:25:90:78:2D:5C UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:0 (0.0 b) Interrupt:16 Memory:f7900000-f7920000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:6 errors:0 dropped:0 overruns:0 frame:0 TX packets:6 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:504 (504.0 b) TX bytes:504 (504.0 b) I have absolutely no clue how to debug this, and I find it very strange since I can still connect via ssh. EDIT: Weirdly, /etc/resolv.conf does not contain any entries, or none that I can make sense of: # Generated by NetworkManager search sui-inter.net # No nameservers found; try putting DNS servers into your # ifcfg files in /etc/sysconfig/network-scripts like so: # # DNS1=xxx.xxx.xxx.xxx # DNS2=xxx.xxx.xxx.xxx # DOMAIN=lab.foo.com bar.foo.com So is it possible that rebooting the server erased that file? It worked before at least! And how do I solve this? By the way, pinging an IP address works.

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• How to implement tail calls in a custom VM

  - by DeadMG

  How can I implement tail calls in a custom virtual machine? I know that I need to pop off the original function's local stack, then it's arguments, then push on the new arguments. But, if I pop off the function's local stack, how am I supposed to push on the new arguments? They've just been popped off the stack.

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• C++ class member functions instantiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched Stack Overflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state information was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (VC++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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