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• write to fifo/pipe from shell, with timeout

  - by Tim

  I have a pair of shell programs that talk over a named pipe. The reader creates the pipe when it starts, and removes it when it exits. Sometimes, the writer will attempt to write to the pipe between the time that the reader stops reading and the time that it removes the pipe. reader: while condition; do read data <$PIPE; do_stuff; done writer: echo $data >>$PIPE reader: rm $PIPE when this happens, the writer will hang forever trying to open the pipe for writing. Is there a clean way to give it a timeout, so that it won't stay hung until killed manually? I know I can do #!/bin/sh # timed_write <timeout> <file> <args> # like "echo <args> >> <file>" with a timeout TIMEOUT=$1 shift; FILENAME=$1 shift; PID=$$ (X=0; # don't do "sleep $TIMEOUT", the "kill %1" doesn't kill the sleep while [ "$X" -lt "$TIMEOUT" ]; do sleep 1; X=$(expr $X + 1); done; kill $PID) & echo "$@" >>$FILENAME kill %1 but this is kind of icky. Is there a shell builtin or command to do this more cleanly (without breaking out the C compiler)?

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• PHP autoloader: ignoring non-existing include

  - by Bart van Heukelom

  I have a problem with my autoloader: public function loadClass($className) { $file = str_replace(array('_', '\\'), '/', $className) . '.php'; include_once $file; } As you can see, it's quite simple. I just deduce the filename of the class and try to include it. I have a problem though; I get an exception when trying to load a non-existing class (because I have an error handler which throws exceptions). This is inconvenient, because it's also fired when you use class_exists() on a non-existing class. You don't want an exception there, just a "false" returned. I fixed this earlier by putting an @ before the include (supressing all errors). The big drawback with this, though, is that any parser/compiler errors (that are fatal) in this include won't show up (not even in the logs), resulting in a hard to find bug. What would be the best way to solve both problems at once? The easiest way would be to include something like this in the autoloader (pseudocode): foreach (path in the include_path) { if (is_readable(the path + the class name)) readable = true; } if (!readable) return; But I worry about the performance there. Would it hurt a lot? (Solved) Made it like this: public function loadClass($className) { $file = str_replace(array('_', '\\'), '/', $className) . '.php'; $paths = explode(PATH_SEPARATOR, get_include_path()); foreach ($paths as $path) { if (is_readable($path . '/' . $file)) { include_once $file; return; } } }

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• Ambiguous access to base class template member function

  - by Johann Gerell

  In Visual Studio 2008, the compiler cannot resolve the call to SetCustomer in _tmain below and make it unambiguous: template <typename TConsumer> struct Producer { void SetConsumer(TConsumer* consumer) { consumer_ = consumer; } TConsumer* consumer_; }; struct AppleConsumer { }; struct MeatConsumer { }; struct ShillyShallyProducer : public Producer<AppleConsumer>, public Producer<MeatConsumer> { }; int _tmain(int argc, _TCHAR* argv[]) { ShillyShallyProducer producer; AppleConsumer consumer; producer.SetConsumer(&consumer); // <--- Ambiguous call!! return 0; } This is the compilation error: // error C2385: ambiguous access of 'SetConsumer' // could be the 'SetConsumer' in base 'Producer<AppleConsumer>' // or could be the 'SetConsumer' in base 'Producer<MeatConsumer>' I thought the template argument lookup mechanism would be smart enough to deduce the correct base Producer. Why isn't it? I could get around this by changing Producer to template <typename TConsumer> struct Producer { template <typename TConsumer2> void SetConsumer(TConsumer2* consumer) { consumer_ = consumer; } TConsumer* consumer_; }; and call SetConsumer as producer.SetConsumer<AppleConsumer>(&consumer); // Unambiguous call!! but it would be nicer if I didn't have to...

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• Creating spotlight in OpenGL scene

  - by Victor Oliveira

  Im studying OpenGL and trying to create a spot light at my application. The code that Im using for my #vertex-shader is below: #:vertex-shader #{ #version 150 core in vec3 in_pos; in vec2 in_tc; out vec2 tc; glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 20.0f); GLfloat spot_direction[] = { -1.0, -1.0, 0.0 }; glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, spot_direction); glEnable(GL_LIGHT0); void main() { vec4 pos= vec4(vec3(1.0)*in_pos - vec3(1.0), 1.0); pos.z=0.0; gl_Position = pos; tc = in_tc; } } The thing is, everytime Im trying to run the code an Error that says: Type: other, Source: api, ID: 131169, Severity: low Message: Framebuffer detailed info: The driver allocated storage for renderbuffer 1. len = 157, written = 0 failed to compile vertex shader of deferred: directional info log for shader deferred: directional vertex info log for shader deferred: directional: ERROR: Unbound variable: when Specifications: Renderer: GeForce GTX 580/PCIe/SSE2 Version: 3.3.0 NVIDIA 319.17 GLSL: 3.30 NVIDIA via Cg compiler Status: Using GLEW 1.9.0 1024 x 768 OS: Linux debian I guess to create this spotlight is pretty much simple, but since Im really new to OpenGL I dont have a clue how to do it until now, even reading sources like: http://www.glprogramming.com/red/chapter05.html#name3 Read also in some place that light spots can get really hard to understand, but I cant avoid this step right now since Im following my lecture schedule. Could anybody help me?

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• Why does autoboxing in Java allow me to have 3 possible values for a boolean?

  - by John

  Reference: http://java.sun.com/j2se/1.5.0/docs/guide/language/autoboxing.html If your program tries to autounbox null, it will throw a NullPointerException. javac will give you a compile-time error if you try to assign null to a boolean. makes sense. assigning null to a Boolean is a-ok though. also makes sense, i guess. but let's think about the fact that you'll get a NPE when trying to autounbox null. what this means is that you can't safely perform boolean operations on Booleans without null-checking or exception handling. same goes for doing math operations on an Integer. for a long time, i was a fan of autoboxing in java1.5+ because I thought it got java closer to be truly object-oriented. but, after running into this problem last night, i gotta say that i think this sucks. the compiler giving me an error when I'm trying to do stuff with an uninitialized primitive is a good thing. I think I may be misunderstanding the point of autoboxing, but at the same time I will never accept that a boolean should be able to have 3 values. can anyone explain this? what am i not getting?

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• Can't install egenix-mx-base on Django production VPS

  - by Shane

  I have been following these instructions for setting up a Django production server with postgres, apache, nginx, and memcache. My problem is that I cannot get egenix-mx-base to install and without this I cannot get psycopg2 to work and therefore no database access :(. I am attempting this on a VPS running a clean install of Ubuntu Hardy (8.04) and have followed all instructions on the site to a T. The error message is as follows: $ easy_install egenix-mx-base Searching for egenix-mx-base Reading http://pypi.python.org/simple/egenix-mx-base/ Reading http://www.egenix.com/products/python/mxBase/ Reading http://www.lemburg.com/python/mxExtensions.html Reading http://www.egenix.com/ Best match: egenix-mx-base 3.1.3 Downloading http://downloads.egenix.com/python/egenix-mx-base-3.1.3.tar.gz Processing egenix-mx-base-3.1.3.tar.gz Running egenix-mx-base-3.1.3/setup.py -q bdist_egg --dist-dir /tmp/easy_install-iF7qzl/egenix-mx-base-3.1.3/egg-dist-tmp-laxvcS Warning: Can't read registry to find the necessary compiler setting Make sure that Python modules _winreg, win32api or win32con are installed. In file included from mx/TextTools/mxTextTools/mxte.c:42: mx/TextTools/mxTextTools/mxte_impl.h: In function ‘mxTextTools_TaggingEngine’: mx/TextTools/mxTextTools/mxte_impl.h:345: warning: pointer targets in initialization differ in signedness mx/TextTools/mxTextTools/mxte_impl.h:364: warning: pointer targets in initialization differ in signedness mx/URL/mxURL/mxURL.c: In function ‘mxURL_SetFromString’: mx/URL/mxURL/mxURL.c:676: warning: pointer targets in initialization differ in signedness mx/UID/mxUID/mxUID.c: In function ‘mxUID_Verify’: mx/UID/mxUID/mxUID.c:333: warning: pointer targets in passing argument 1 of ‘sscanf’ differ in signedness mx/UID/mxUID/mxUID.c: In function ‘mxUID_New’: mx/UID/mxUID/mxUID.c:462: warning: pointer targets in passing argument 1 of ‘mxUID_CRC16’ differ in signedness error: Setup script exited with error: build/bdist.linux-x86_64-py2.5_ucs4/dumb/egenix_mx_base-3.1.3-py2.5.egg-info: Is a directory Thank you to anyone who takes the time to try to help me.

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• How to use void*

  - by Rondogiannis Aristophanes

  I am imlementing a simple merge function and I have got stuck, as the compiler gives me errors that I cannot explain. Here is my merge function: void merge(void *a, int beg, int middle, int end, int (*cmp)(const void*, const void* { std::stack<void*> first; std::stack<void*> second; for(int i = beg; i < middle; i++) { first.push(a+i); } for(int i = middle; i < end; i++) { second.push(a+i); } for(int i = beg; i < end; i++) { if(first.empty()) { void *tmp = second.top(); second.pop(); a+i = tmp; } else if(second.empty()) { void *tmp = first.top(); first.pop(); a+i = tmp; } else if(cmp(first.top(), second.top())) { void *tmp = first.top(); first.pop(); a+i = tmp; } else { void *tmp = second.top(); second.pop(); a+i = tmp; } } } And here is the error: sort.h: In function `void merge(void*, int, int, int, int (*)(const void*, const void*))': sort.h:9: error: pointer of type `void *' used in arithmetic sort.h:12: error: pointer of type `void *' used in arithmetic sort.h:19: error: pointer of type `void *' used in arithmetic sort.h:19: error: non-lvalue in assignment sort.h:23: error: pointer of type `void *' used in arithmetic sort.h:23: error: non-lvalue in assignment sort.h:27: error: pointer of type `void *' used in arithmetic sort.h:27: error: non-lvalue in assignment sort.h:31: error: pointer of type `void *' used in arithmetic sort.h:31: error: non-lvalue in assignment Can anyone help me? TIA.

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• Use Objective-C without NSObject?

  - by Alex I

  I am testing some simple Objective-C code on Windows (cygwin, gcc). This code already works in Xcode on Mac. I would like to convert my objects to not subclass NSObject (or anything else, lol). Is this possible, and how? What I have so far: // MyObject.h @interface MyObject - (void)myMethod:(int) param; @end and // MyObject.m #include "MyObject.h" @interface MyObject() { // this line is a syntax error, why? int _field; } @end @implementation MyObject - (id)init { // what goes in here? return self; } - (void)myMethod:(int) param { _field = param; } @end What happens when I try compiling it: gcc -o test MyObject.m -lobjc MyObject.m:4:1: error: expected identifier or ‘(’ before ‘{’ token MyObject.m: In function ‘-[MyObject myMethod:]’: MyObject.m:17:3: error: ‘_field’ undeclared (first use in this function) EDIT My compiler is cygwin's gcc, also has cygwin gcc-objc package: gcc --version gcc (GCC) 4.7.3 I have tried looking for this online and in a couple of Objective-C tutorials, but every example of a class I have found inherits from NSObject. Is it really impossible to write Objective-C without Cocoa or some kind of Cocoa replacement that provides NSObject? (Yes, I know about GNUstep. I would really rather avoid that if possible...)

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• Convert Form to UserControl

  - by Joe

  I have a 3rd party code library that I'm using; part of this library is a winforms application for editing the configuration files used by this library. I would like to embed their configuration editor app into my application. I have the source code to their library and the configuration editor is (as far as I can tell) a straight forward Winforms app using standard controls. I'm trying to convert the app's main form into a UserControl so that I can host it inside my application which is WPF (WPF's WindowsFormsHost won't host a Form object, I get an exception). I changed the form object to inherit from UserControl instead of Form and fixed all the compiler errors (there weren't many, just property initializations that don't exist on UserControls) but what's happening is my newly converted control is just blank. When I run my test app I don't see any of the controls that make up the original form, just a blank page. Any ideas? I really don't want to have to re-implement their app from scratch, that would suck. Edit: I forgot to mention I'm testing this in a WinForms application, not WPF, to just get the control working before trying to use it from WPF.

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• ASP.NET SQLMembership Provider not logging in

  - by cfdev9

  My web app uses the sql memebership provider. Running it locally all is well, deploying to a dev server it works fine too in firefox, but in IE8 something unexpected is happening. Once a user logs in they're supposed to be redirected to home.aspx. What's happening when I attempt to login is it appears to accept the login credentials but then doesn't redirect to home.aspx. Instead it just redirects me to the login page as though I had attempted to access home.aspx directly without being logged in. The url parameter ReturnUrl is appended, Login.aspx?ReturnUrl=%2fhome.aspx Why is this only happening with IE8? My local PC is IIS7 but the server is IIS6. Using the same web.config Full code behind public partial class Login : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { Session.Abandon(); FormsAuthentication.SignOut(); } } protected void btnSubmit_Click(object sender, EventArgs e) { if (Membership.ValidateUser(tbUsername.Text, tbPassword.Text)) { if (Request.QueryString["ReturnUrl"] != null) { FormsAuthentication.RedirectFromLoginPage(tbUsername.Text, false); } else { FormsAuthentication.SetAuthCookie(tbUsername.Text, false); Response.Redirect("~/Home.aspx"); } } } } Full web.config <?xml version="1.0"?> <configuration> <configSections> <sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"> <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"> <section name="scriptResourceHandler" type="System.Web.Configuration.ScriptingScriptResourceHandlerSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/> <sectionGroup name="webServices" type="System.Web.Configuration.ScriptingWebServicesSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"> <section name="jsonSerialization" type="System.Web.Configuration.ScriptingJsonSerializationSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="Everywhere"/> <section name="profileService" type="System.Web.Configuration.ScriptingProfileServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/> <section name="authenticationService" type="System.Web.Configuration.ScriptingAuthenticationServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/> <section name="roleService" type="System.Web.Configuration.ScriptingRoleServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/> </sectionGroup> </sectionGroup> </sectionGroup> </configSections> <appSettings/> <connectionStrings> <add name="ASPNET_DB" connectionString="..."/> </connectionStrings> <system.web> <membership defaultProvider="SqlMembershipProvider"> <providers> <add name="SqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" connectionStringName="ASPNET_DB" enablePasswordRetrieval="true" enablePasswordReset="true" requiresQuestionAndAnswer="false" applicationName="/" requiresUniqueEmail="false" passwordFormat="Clear" maxInvalidPasswordAttempts="5" passwordAttemptWindow="10" passwordStrengthRegularExpression="" minRequiredPasswordLength="1" minRequiredNonalphanumericCharacters="0"/> </providers> </membership> <roleManager enabled="true" defaultProvider="SqlRoleManager"> <providers> <add name="SqlRoleManager" type="System.Web.Security.SqlRoleProvider" connectionStringName="ASPNET_DB" applicationName="/"/> </providers> </roleManager> <authentication mode="Forms"> <forms name="CHOUSE.ASPXAUTH" loginUrl="login.aspx" protection="All" path="/"/> </authentication> <authorization> <allow roles="AccountManager"/> <allow roles="Client"/> <deny users="*"/> </authorization> <compilation debug="true"> <assemblies> <add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/> <add assembly="System.Data.DataSetExtensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/> <add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> <add assembly="System.Xml.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/> </assemblies> </compilation> <pages> <controls> <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> <add tagPrefix="asp" namespace="System.Web.UI.WebControls" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> </controls> </pages> <httpHandlers> <remove verb="*" path="*.asmx"/> <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> <add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> <add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false"/> </httpHandlers> <httpModules> <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> </httpModules> </system.web> <location path="Admin"> <system.web> <authorization> <allow roles="AccountManager"/> <deny users="*"/> </authorization> </system.web> </location> <system.codedom> <compilers> <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <providerOption name="CompilerVersion" value="v3.5"/> <providerOption name="WarnAsError" value="false"/> </compiler> </compilers> </system.codedom> <system.webServer> <validation validateIntegratedModeConfiguration="false"/> <modules> <remove name="ScriptModule"/> <add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> </modules> <handlers> <remove name="WebServiceHandlerFactory-Integrated"/> <remove name="ScriptHandlerFactory"/> <remove name="ScriptHandlerFactoryAppServices"/> <remove name="ScriptResource"/> <add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> <add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> <add name="ScriptResource" preCondition="integratedMode" verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> </handlers> </system.webServer> <runtime> <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> <dependentAssembly> <assemblyIdentity name="System.Web.Extensions" publicKeyToken="31bf3856ad364e35"/> <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/> </dependentAssembly> <dependentAssembly> <assemblyIdentity name="System.Web.Extensions.Design" publicKeyToken="31bf3856ad364e35"/> <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/> </dependentAssembly> </assemblyBinding> </runtime>

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• How do I write test code to exercise a C# generic Pair<TKey, TValue> ?

  - by Scott Davies

  Hi, I am reading through Jon Skeet's "C# in Depth", first edition (which is a great book). I'm in section 3.3.3, page 84, "Implementing Generics". Generics always confuse me, so I wrote some code to exercise the sample. The code provided is: using System; using System.Collections.Generic; public sealed class Pair<TFirst, TSecond> : IEquatable<Pair<TFirst, TSecond>> { private readonly TFirst first; private readonly TSecond second; public Pair(TFirst first, TSecond second) { this.first = first; this.second = second; } ...property getters... public bool Equals(Pair<TFirst, TSecond> other) { if (other == null) { return false; } return EqualityComparer<TFirst>.Default.Equals(this.First, other.First) && EqualityComparer<TSecond>.Default.Equals(this.Second, other.Second); } My code is: class MyClass { public static void Main (string[] args) { // Create new pair. Pair thePair = new Pair(new String("1"), new String("1")); // Compare a new pair to previous pair by generating a second pair. if (thePair.Equals(new Pair(new string("1"), new string("1")))) System.Console.WriteLine("Equal"); else System.Console.WriteLine("Not equal"); } } The compiler complains: "Using the generic type 'ManningListing36.Paie' requires 2 type argument(s) CS0305" What am I doing wrong ? Thanks, Scott

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• How to allow users to define financial formulas in a C# app

  - by Peter Morris

  I need to allow my users to be able to define formulas which will calculate values based on data. For example //Example 1 return GetMonetaryAmountFromDatabase("Amount due") * 1.2; //Example 2 return GetMonetaryAmountFromDatabase("Amount due") * GetFactorFromDatabase("Discount"); I will need to allow / * + - operations, also to assign local variables and execute IF statements, like so var amountDue = GetMonetaryAmountFromDatabase("Amount due"); if (amountDue > 100000) return amountDue * 0.75; if (amountDue > 50000) return amountDue * 0.9; return amountDue; The scenario is complicated because I have the following structure.. Customer (a few hundred) Configuration (about 10 per customer) Item (about 10,000 per customer configuration) So I will perform a 3 level loop. At each "Configuration" level I will start a DB transaction and compile the forumlas, each "Item" will use the same transaction + compiled formulas (there are about 20 formulas per configuration, each item will use all of them). This further complicates things because I can't just use the compiler services as it would result in continued memory usage growth. I can't use a new AppDomain per each "Configuration" loop level because some of the references I need to pass cannot be marshalled. Any suggestions?

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• How can I make a Maybe-Transformer MaybeT into an instance of MonadWriter?

  - by martingw

  I am trying to build a MaybeT-Transformer Monad, based on the example in the Real World Haskell, Chapter Monad Transformers: data MaybeT m a = MaybeT { runMT :: m (Maybe a) } instance (Monad m) => Monad (MaybeT m) where m >>= f = MaybeT $ do a <- runMT m case a of Just x -> runMT (f x) Nothing -> return Nothing return a = MaybeT $ return (Just a) instance MonadTrans MaybeT where lift m = MaybeT $ do a <- m return (Just a) This works fine, but now I want to make MaybeT an instance of MonadWriter: instance (MonadWriter w m) => MonadWriter w (MaybeT m) where tell = lift . tell listen m = MaybeT $ do unwrapped <- listen (runMT m) return (Just unwrapped) The tell is ok, but I can't get the listen function right. The best I could come up with after 1 1/2 days of constructor origami is the one you see above: unwrapped is supposed to be a tuple of (Maybe a, w), and that I want to wrap up in a Maybe-Type and put the whole thing in an empty MonadWriter. But the compiler complains with: Occurs check: cannot construct the infinite type: a = Maybe a When generalising the type(s) for `listen' In the instance declaration for `MonadWriter w (MaybeT m)' What am I missing?

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• What are the benefits of the PHP the different PHP compression libraries?

  - by Christopher W. Allen-Poole

  I've been looking into ways to compress PHP libraries, and I've found several libraries which might be useful, but I really don't know much about them. I've specifically been reading about bcompiler and PHAR libraries. Is there any performance benefit in either of these? Are there any "gotchas" I need to watch out for? What are the relative benefits? Do either of them add to/detract from performance? I'm also interested in learning of other libs which might be out there which are not obvious in the documentation? As an aside, does anyone happen to know whether these work more like zip files which just happen to have the code in there, or if they operate more like Python's pre-compiling which actually runs a pseudo-compiler? ======================= EDIT ======================= I've been asked, "What are you trying to accomplish?" Well, I suppose the answer is that this is all hypothetical. It is a combination of these: What if my pet project becomes the most popular web project on earth and I want to distribute it quickly and easily? (hay, a man can dream, right?) It also seems if using PHAR can be done easily, it would be the best way to create a subversion snapshot. Python has this really cool pre-compiling policy, I wonder if PHP has something like that? These libraries seem to do something similar. Will they do that? Hey, these libraries seem pretty neat, but I'd like clarification on the differences as they seem to do the same thing

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• Use of var keyword in C#

  - by kronoz

  After discussion with colleagues regarding the use of the 'var' keyword in C# 3 I wondered what people's opinions were on the appropriate uses of type inference via var? For example I rather lazily used var in questionable circumstances, e.g.:- foreach(var item in someList) { // ... } // Type of 'item' not clear. var something = someObject.SomeProperty; // Type of 'something' not clear. var something = someMethod(); // Type of 'something' not clear. More legitimate uses of var are as follows:- var l = new List<string>(); // Obvious what l will be. var s = new SomeClass(); // Obvious what s will be. Interestingly LINQ seems to be a bit of a grey area, e.g.:- var results = from r in dataContext.SomeTable select r; // Not *entirely clear* what results will be here. It's clear what results will be in that it will be a type which implements IEnumerable, however it isn't entirely obvious in the same way a var declaring a new object is. It's even worse when it comes to LINQ to objects, e.g.:- var results = from item in someList where item != 3 select item; This is no better than the equivilent foreach(var item in someList) { // ... } equivilent. There is a real concern about type safety here - for example if we were to place the results of that query into an overloaded method that accepted IEnumerable<int> and IEnumerable<double> the caller might inadvertently pass in the wrong type. Edit - var does maintain strong typing but the question is really whether it's dangerous for the type to not be immediately apparent on definition, something which is magnified when overloads mean compiler errors might not be issued when you unintentionally pass the wrong type to a method. Related Question: http://stackoverflow.com/questions/633474/c-do-you-use-var

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• Calling a method on an unitialized object (null pointer)

  - by Florin

  What is the normal behavior in Objective-C if you call a method on an object (pointer) that is nil (maybe because someone forgot to initialize it)? Shouldn't it generate some kind of an error (segmentation fault, null pointer exception...)? If this is normal behavior, is there a way of changing this behavior (by configuring the compiler) so that the program raises some kind of error / exception at runtime? To make it more clear what I am talking about, here's an example. Having this class: @interface Person : NSObject { NSString *name; } @property (nonatomic, retain) NSString *name; - (void)sayHi; @end with this implementation: @implementation Person @synthesize name; - (void)dealloc { [name release]; [super dealloc]; } - (void)sayHi { NSLog(@"Hello"); NSLog(@"My name is %@.", name); } @end Somewhere in the program I do this: Person *person = nil; //person = [[Person alloc] init]; // let's say I comment this line person.name = @"Mike"; // shouldn't I get an error here? [person sayHi]; // and here [person release]; // and here

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• How can I get bitfields to arrange my bits in the right order?

  - by Jim Hunziker

  To begin with, the application in question is always going to be on the same processor, and the compiler is always gcc, so I'm not concerned about bitfields not being portable. gcc lays out bitfields such that the first listed field corresponds to least significant bit of a byte. So the following structure, with a=0, b=1, c=1, d=1, you get a byte of value e0. struct Bits { unsigned int a:5; unsigned int b:1; unsigned int c:1; unsigned int d:1; } __attribute__((__packed__)); (Actually, this is C++, so I'm talking about g++.) Now let's say I'd like a to be a six bit integer. Now, I can see why this won't work, but I coded the following structure: struct Bits2 { unsigned int a:6; unsigned int b:1; unsigned int c:1; unsigned int d:1; } __attribute__((__packed__)); Setting b, c, and d to 1, and a to 0 results in the following two bytes: c0 01 This isn't what I wanted. I was hoping to see this: e0 00 Is there any way to specify a structure that has three bits in the most significant bits of the first byte and six bits spanning the five least significant bits of the first byte and the most significant bit of the second? Please be aware that I have no control over where these bits are supposed to be laid out: it's a layout of bits that are defined by someone else's interface.

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• A question on delegates and method parameters

  - by Srinivas Reddy Thatiparthy

  public class Program { delegate void Srini(string param); static void Main(string[] args) { Srini sr = new Srini(PrintHello1); sr += new Srini(PrintHello2); //case 2: sr += new Srini(delegate(string o) { Console.WriteLine(o); }); sr += new Srini(delegate(object o) { Console.WriteLine(o.ToString()); }); //case 4: sr += new Srini(delegate { Console.WriteLine(“This line is accepted,though the method signature is not Comp”); });//case 5 sr("Hello World"); Console.Read(); } static void PrintHello1(string param) { Console.WriteLine(param); } static void PrintHello2(object param) { Console.WriteLine(param); } } Compiler doesn't complain about the case 2(see the comment),well,the reason is straight forward since string inherits from object. ,along the same lines ,Why is it complaining for anonymous method types(see the comment //case 4:) that “Cannot convert anonymous method to delegate type 'DelegateTest.Program.Srini' because the parameter types do not match the delegate parameter types” where as in case of normal method it doesn't ?or am i comparing apples with oranges? Another case is why is it accepting anonymous method without parameters?

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• how do i execute a stored procedure with vici coolstorage?

  - by lincolnk

  I'm building an app around Vici Coolstorage (asp.net version). I have my classes created and mapped to my database tables and can pull a list of all records fine. I've written a stored procedure where the query jumps across databases that aren't mapped with Coolstorage, however, the fields in the query result map directly to one of my classes. The procedure takes 1 parameter. so 2 questions here: how do i execute the stored procedure? i'm doing this CSParameterCollection collection = new CSParameterCollection(); collection.Add("@id", id); var result = Vici.CoolStorage.CSDatabase.RunQuery("procedurename", collection); and getting the exception "Incorrect syntax near 'procedurename'." (i'm guessing this is because it's trying to execute it as text rather than a procedure?) and also, since the class representing my table is defined as abstract, how do i specify that result should create a list of MyTable objects instead of generic or dynamic or whatever objects? if i try Vici.CoolStorage.CSDatabase.RunQuery<MyTable>(...) the compiler yells at me for it being an abstract class.

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• Ignore LD_LIBRARY_PATH and stick with library given through -rpath at link time

  - by roe

  I'm sitting in an environment which I have no real control over (it's not just me, so basically, I can't change the environment or it won't work for anyone else), the only thing I can affect is how the binary is built. My problem is, the environment specifies an LD_LIBRARY_PATH containing a libstdc++ which is not compatible with the compiler being used. I tried compiling it statically, but that doesn't seem possible for g++ (version 4.2.3, seems to have been work done in this direction in later versions though which are not available, -static-libstdc++ or something like that). Now I've arrived at using rpath to bake the absolute path name into the executable (would work, all machines it's supposed to run on are identical). Unfortunately it appears as though LD_LIBRARY_PATH takes precedence over rpath (resetting LD_LIBRARY_PATH confirmed that it's able to find the library, but as stated above, LD_LIBRARY_PATH will be set for everyone, and I cannot change that). Is there any way I can make rpath take precedence over LD_LIBRARY_PATH, or are there any other possible solutions to my problem? Note that I'm talking about dynamic linking at runtime, I am able to control the command line at compile and link time. Thanks.

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• Setting Up OpenCV and .lib files

  - by jhaip

  I have been trying to set up OpenCV for the past few days with no results. I am using Windows 7 and VS C++ 2008 express edition. I have downloaded and installed OpenCV 2.1 and some of the examples work. I downloaded CMake and ran it to generate the VS project files and built all of them but there with several errors, and couldn't get any farther than that. When I ran CMake I configured it to use the VS 9 compiler, and then it brought up a list of items in red such as BUILD_EXAMPLES, BUILD_LATEX_DOCS, ect. All of them were unchecked except BUILD_NEW_PYTHON_SUPPORT, BUILD_TESTS, ENABLE_OPENMP, and OPENCV_BUILD_3RDPARTY_LIBS. I configured and generate without changing anything and then it generated the VS files such as ALL_BUILD.vcproj. I built the OpenCV VS solution in debug mode and it had 15 failures (maybe this is part of the problem or is it because I don't have python and stuff like that?) Now there was a lib folder created after building but inside there was just this VC++ Minimum Rebuild Dependency file and Program Debug Database file, both called cvhaartraining. I believe it should have created the .lib files I need instead of this. Also, the bin folder now has a folder called Debug with the same types of files with names like cv200d and cvaux200d. Believe I need those .lib files to move forward. I would also greatly appreciate if someone could direct me to a reliable tutorial to set up VS for OpenCV because I have been reading a lot of tutorials and they all say different things such as some say to configure Window's environment variables and other say files are located in folders such as OpenCV/cv which I don't have. I have gotten past the point of clear headed thinking so if anyone could offer some direction or a simple list of the files I need to link then I would be thankful. Also a side question: why when linking the OpenCV libs do you have to put them in quotes?

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• C++ Unary - Operator Overload Won't Compile

  - by Brian Hooper

  I am attempting to create an overloaded unary - operator but can't get the code to compile. A cut-down version of the code is as follows:- class frag { public: frag myfunc (frag oper1, frag oper2); frag myfunc2 (frag oper1, frag oper2); friend frag operator + (frag &oper1, frag &oper2); frag operator - () { frag f; f.element = -element; return f; } private: int element; }; frag myfunc (frag oper1, frag oper2) { return oper1 + -oper2; } frag myfunc2 (frag oper1, frag oper2) { return oper1 + oper2; } frag operator+ (frag &oper1, frag &oper2) { frag innerfrag; innerfrag.element = oper1.element + oper2.element; return innerfrag; } The compiler reports... /home/brian/Desktop/frag.hpp: In function ‘frag myfunc(frag, frag)’: /home/brian/Desktop/frag.hpp:41: error: no match for ‘operator+’ in ‘oper1 + oper2.frag::operator-()’ /home/brian/Desktop/frag.hpp:16: note: candidates are: frag operator+(frag&, frag&) Could anyone suggest what I need to be doing here? Thanks.

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• Whats the wrong with this code?

  - by girinie

  Hi in this code first I am downloading a web-page source code then I am storing the code in text file. Again I am reading that file and matching with the regex to search a specific string. There is no compiler error. Exception in thread "main" java.lang.NoClassDefFoundError: java/lang/CharSequence Can anybody tell me Where I am wrong. import java.io.*; import java.net.*; import java.lang.*; import java.util.regex.Matcher; import java.util.regex.Pattern; public class WebDownload { public void getWebsite() { try{ URL url=new URL("www.gmail.com");// any URL can be given URLConnection urlc=url.openConnection(); BufferedInputStream buffer=new BufferedInputStream(urlc.getInputStream()); StringBuffer builder=new StringBuffer(); int byteRead; FileOutputStream fout; StringBuffer contentBuf = new StringBuffer(); while((byteRead=buffer.read()) !=-1) { builder.append((char)byteRead); fout = new FileOutputStream ("myfile3.txt"); new PrintStream(fout).println (builder.toString()); fout.close(); } BufferedReader in = new BufferedReader(new FileReader("myfile3.txt")); String buf = null; while ((buf = in.readLine()) != null) { contentBuf.append(buf);contentBuf.append("\n"); } in.close(); Pattern p = Pattern.compile("<div class=\"summarycount\">([^<]*)</div>"); Matcher matcher = p.matcher(contentBuf); if(matcher.find()) { System.out.println(matcher.group(1)); } else System.out.println("could not find"); } catch(MalformedURLException ex) { ex.printStackTrace(); } catch(IOException ex){ ex.printStackTrace(); } } public static void main(String [] args) { WebDownload web=new WebDownload(); web.getWebsite(); } }

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• structure inside structure - c++ Error

  - by gamadeus

  First of all the error I am getting is of the type: Request for member 's' of struct1.struct1::struct2, which is of non class type '__u32' where: struct struct1 { struct x struct2; struct x struct3; struct x struct4; }; The usage is of the form: struct struct1 st1; st1.struct2.s = Value; Now my struct1 is: struct ip_mreq_source { struct in_addr imr_multiaddr; struct in_addr imr_sourceaddr; struct in_addr imr_interface; }; struct 'x' is in_addr Where: typedef uint32_t in_addr_t; struct in_addr { in_addr_t s_addr; }; element 's' is the element s_addr in in_addr. My detailed error coming out of g++ (GCC 4.4.3) from the Android based compiler: arm-linux-androideabi-g++ -MMD -MP -MF groupsock/GroupsockHelper.o.d.org -fpic -ffunction-sections -funwind-tables -fstack-protector -D__ARM_ARCH_5__ -D__ARM_ARCH_5T__ -D__ARM_ARCH_5E__ -D__ARM_ARCH_5TE__ -Wno-psabi -march=armv5te -mtune=xscale -msoft-float -fno-exceptions -fno-rtti -mthumb -Os -fomit-frame-pointer -fno-strict-aliasing -finline- limit=64 -Igroupsock/include -Igroupsock/../UsageEnvironment/include -Iandroid- ndk-r5b/sources/cxx-stl/system/include -Igroupsock -DANDROID -Wa,--noexecstack -DANDROID_NDK -Wall -fexceptions -O2 -DNDEBUG -g -Iandroid-8/arch-arm/usr/include -c groupsock/GroupsockHelper.cpp -o groupsock/GroupsockHelper.o && rm -f groupsock/GroupsockHelper.o.d && mv groupsock/GroupsockHelper.o.d.org groupsock/GroupsockHelper.o.d groupsock/GroupsockHelper.cpp: In function 'Boolean socketJoinGroupSSM(UsageEnvironment&, int, netAddressBits, netAddressBits)': groupsock/GroupsockHelper.cpp:427: error: request for member 's_addr' in 'imr.ip_mreq_source::imr_multiaddr', which is of non-class type '__u32' groupsock/GroupsockHelper.cpp:428: error: request for member 's_addr' in 'imr.ip_mreq_source::imr_sourceaddr', which is of non-class type '__u32' groupsock/GroupsockHelper.cpp:429: error: request for member 's_addr' in 'imr.ip_mreq_source::imr_interface', which is of non-class type '__u32' I am not sure what is causing the error. Any pointers would be great - no pun intended. Thanks

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• How do I tell gcc to relax its restrictions on typecasting when calling a C function from C++?

  - by Daryl Spitzer

  I'm trying to use Cmockery to mock C functions called from C++ code. Because the SUT is in C++, my tests need to be in C++. When I use the Cmockery expect_string() macro like this: expect_string(mock_function, url, "Foo"); I get: my_tests.cpp: In function ‘void test_some_stuff(void**)’: my_tests.cpp:72: error: invalid conversion from ‘void*’ to ‘const char*’ my_tests.cpp:72: error: initializing argument 5 of ‘void _expect_string(const char*, const char*, const char*, int, const char*, int)’ I see in cmockery.h that expect_string is defined: #define expect_string(function, parameter, string) \ expect_string_count(function, parameter, string, 1) #define expect_string_count(function, parameter, string, count) \ _expect_string(#function, #parameter, __FILE__, __LINE__, (void*)string, \ count) And here's the prototype for _expect_string (from cmockery.h): void _expect_string( const char* const function, const char* const parameter, const char* const file, const int line, const char* string, const int count); I believe the problem is that I'm compiling C code as C++, so the C++ compiler is objecting to (void*)string in the expect_string_count macro being passed as the const char* string parameter to the _expect_string() function. I've already used extern "C" around the cmockery.h include in my_tests.cpp like this: extern "C" { #include <cmockery.h> } ...in order to get around name-mangling problems. (See "How do I compile and link C++ code with compiled C code?") Is there a command-line option or some other means of telling g++ how to relax its restrictions on typecasting from my test's C++ code to the C function in cmockery.c? This is the command I'm currently using to build my_tests.cpp: g++ -m32 -I ../cmockery-0.1.2 -c my_tests.cpp -o $(obj_dir)/my_tests.o

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