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• how to databind a datalist's page index to a button's commandname?

  - by korben

  i got this inside a button inside a datalist CommandName="<%# Container.ItemIndex %>" when i click the button, i'm expecting commandname to = 0, then 1, then 2, etc, as the datalist progresses, and i'm using that value in the button click's c# but i'm getting this error, i'm pretty sure i'm using this exact setup on another page and i have no problems, any idea what's going on? Server Error in '/' Application. Compilation Error Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. Compiler Error Message: CS0117: 'System.Web.UI.Control' does not contain a definition for 'ItemIndex'

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• Are C++ Templates just Macros in disguise?

  - by Roddy

  I've been programming in C++ for a few years, and I've used STL quite a bit and have created my own template classes a few times to see how it's done. Now I'm trying to integrate templates deeper into my OO design, and a nagging thought keeps coming back to me: They're just a macros, really... You could implement (rather UGLY) auto_ptrs using #defines, if you really wanted to. This way of thinking about templates helps me understand how my code will actually work, but I feel that I must be missing the point somehow. Macros are meant evil incarnate, yet "template metaprogramming" is all the rage. So, what ARE the real distinctions? and how can templates avoid the dangers that #define leads you into, like Inscrutable compiler errors in places where you don't expect them? Code bloat? Difficulty in tracing code? Setting Debugger Breakpoints?

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• Fast comparison of char arrays?

  - by StackedCrooked

  I'm currently working in a codebase where IPv4 addresses are represented as pointers to u_int8. The equality operator is implemented like this: bool Ipv4Address::operator==(const u_int8 * inAddress) const { return (*(u_int32*) this->myBytes == *(u_int32*) inAddress); } This is probably the fasted solution, but it causes the GCC compiler warning: ipv4address.cpp:65: warning: dereferencing type-punned pointer will break strict-aliasing rules How can I rewrite the comparison correctly without breaking strict-aliasing rules and without losing performance points? I have considered using either memcmp or this macro: #define IS_EQUAL(a, b) \ (a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3]) I'm thinking that the macro is the fastest solution. What do you recommend?

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• How would one call std::forward on all arguments in a variadic function?

  - by Noah Roberts

  I was just writing a generic object factory and using the boost preprocessor meta-library to make a variadic template (using 2010 and it doesn't support them). My function uses rval references and std::forward to do perfect forwarding and it got me thinking...when C++0X comes out and I had a standard compiler I would do this with real variadic templates. How though, would I call std::forward on the arguments? template < typename ... Params void f(Params ... params) // how do I say these are rvalue reference? { y(std::forward(...params)); //? - I doubt this would work. } Only way I can think of would require manual unpacking of ...params and I'm not quite there yet either. Is there a quicker syntax that would work?

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• boost variant static_visitor problem picking correct function

  - by Steve

  I'm sure I'm having a problem with template resolution here, but I'm not sure why I'm having the problem. I have a static visitor I'm passing to boost variant where i've had to do template specialization for certain cases. The case for everything except for MyClass should throw in the static_visitor below. Unfortunately, when the visitor is applied to pull a MyClass out, it selects the most generic case rather than the exact match. I would type each case explicitly, but that will be rather long. So, why is the compiler resolving the most generic case over the exact match, and is there anyway to fix it template<> class CastVisitor<MyClass>:public boost::static_visitor<MyClass> { public: template<typename U> MyClass operator()(const U & i) const { throw std::exception("Unable to cast"); } MyClass operator()(const MyClass& i) { return i; } };

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• how to access child instances in a vector in c++

  - by tsubasa

  I have a parent class and child class (inherited from parent). In the child class, I have a member function named function_blah(); I used vector<parent*> A to store 5 parent instances, 3 child instances. So the total number of elements in the vector is 8. I can easily access to member functions of element A[0] to A[4], which are parent instances. But whenever I try to have access to member functions of element A[5] to A[7], the compiler complains that class parent has no member named 'function_blah' The way I access to elements is using index. e.x A[i] with i = 0..7. Is it correct? if not, how?

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• Visual Studio 2010 Compiling C code

  - by Corsen2000

  I have the following code snippet. This is a c file in visual studio 2010. If i try to compile this with the line: int hello = 10; commented out it will compile just fine. If I comment that line in it will not compile. Am I missing something or should I not be using Visual Studio 2010 to compile C code. If this is a Visual Studio problem can anyone recommend a easy to use IDE / Compiler that I can for C. Thank You int* x = (int*) calloc(1, sizeof(int)); *x = 5; //int hello = 10; printf("Hello World! %i", *x); getchar();

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• Pass an event into a constructor

  - by Vaccano

  I have a class that I want to be able the handle the mouse up event for a grid. I tried to create it with a static method call like this: MyDataBinding.BindObjectsToDataGrid(ListOfObjectsToBind, myGrid.MouseUp); The end goal being that in the method I would assign a delegate to the MouseUp PassedInMouseUp += myMethodThatWillHandleTheMouseUp; Looks good here (to me) but the compiler chokes on the first line. It says that I can only use MouseUp with a += or a -=. Clearly I am going about this the wrong way. How can I get a different class to handle the mouse up with out having to: Pass in the whole grid Expose the method that will be handling the mouse up as a public method. Or, is this just a limitation and I will have to do one of the above?

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• Operator as and generic classes

  - by abatishchev

  I'm writing .NET On-the-Fly compiler for CLR scripting and want execution method make generic acceptable: object Execute() { return type.InvokeMember(..); } T Execute<T>() { return Execute() as T; /* doesn't work: The type parameter 'T' cannot be used with the 'as' operator because it does not have a class type constraint nor a 'class' constraint */ // also neither typeof(T) not T.GetType(), so on are possible return (T) Execute(); // ok } But I think operator as will be very useful: if result type isn't T method will return null, instead of an exception! Is it possible to do?

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• Can I add a custom method to Core Data-generated classes?

  - by Andy

  I've got a couple of Core Data-generated class files that I'd like to add custom methods to. I don't need to add any instance variables. How can I do this? I tried adding a category of methods: // ContactMethods.h (my category on Core Data-generated "Contact" class) #import "Contact.h" @interface Contact (ContactMethods) -(NSString*)displayName; @end ... // ContactMethods.m #import "ContactMethods.h" @implementation Contact (ContactMethods) -(NSString*)displayName { return @"Some Name"; // this is test code } @end This doesn't work, though. I get a compiler message that "-NSManagedObject may not respond to 'displayName' " and sure enough, when I run the app, I don't get "Some Name" where I should be seeing it.

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• Operators vs Functions in C/C++

  - by user356106

  Someone recently asked me the difference between a C++ standard operator (e.g. new,delete,sizeof) and function (e.g. tan,delete, malloc). By "standard" I mean those provided by default by the compiler suite, and not user defined. Below were the answers I gave, though neither seemed satisfactory. (1) An operator doesn't need any headers to be included to use it : E.g. you can have a call to new without including any headers. However, a function (say free() ) does need headers included, compulsorily. (2) An operator is defined as such (ie as a class operator) somewhere in the standard headers. A function isn't. Can you critique these answers and give me a better idea of the difference?

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• Operations on 64bit words in 32bit system

  - by Vilo

  I'm new here same as I'm new with assembly. I hope that you can help me to start. I'm using 32bit (i686) Ubuntu to make programs in assembly, using gcc compiler. I know that general-purpose-registers are 32bit (4 bytes) max, but what when I have to operate on 64 bit numbers? Intel's instruction says that higher bits are stored in %edx and lower in %eax Great... So how can I do something with this 2-registers number? I have to convert 64bit dec to bin, then save it to memory and show on the screen. How to make the 64bit quadword at start of the program in .data section?

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• Constant embedded for loop condition optimization in C++ with gcc

  - by solinent

  Will a compiler optimize tihs: bool someCondition = someVeryTimeConsumingTask(/* ... */); for (int i=0; i<HUGE_INNER_LOOP; ++i) { if (someCondition) doCondition(i); else bacon(i); } into: bool someCondition = someVeryTimeConsumingTask(/* ... */); if (someCondition) for (int i=0; i<HUGE_INNER_LOOP; ++i) doCondition(i); else for (int i=0; i<HUGE_INNER_LOOP; ++i) bacon(i); someCondition is trivially constant within the for loop. This may seem obvious and that I should do this myself, but if you have more than one condition then you are dealing with permuatations of for loops, so the code would get quite a bit longer. I am deciding on whether to do it (I am already optimizing) or whether it will be a waste of my time.

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• How to know record has been updated successfully in php

  - by Lisa Ray

  $sql = "UPDATE...."; if(mysql_query($sql)) { $_SESSION['Trans']="COMMIT"; header("location:result.php"); exit; } else { $_SESSION['Trans']="FAIL"; $_SESSION['errors'] = "Error: Sorry! We are unable to update your Profile, Please contact to PNP HelpDesk."; header("location:result.php"); exit; }//end IF data is getting updated then why compiler is not coming inside IF condition.

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• Whats the difference between a C++ and a Cocoa Project in Xcode?

  - by david

  I need to work with TagLib for my project. I've created a framework (and I tried using it as a lib) but the compiler cannot find #include < strings on compiling (No such file or Directory). I've created a test C++ project and it #includes < strings just fine. I've looked at the project settings and I cannot find a difference between them. But the standard cocoa projects obviously so not have the search path set to include C++ libraries (Or am I completely getting it wrong?). I've searched for a solution but no one else seems to have run into this problem.

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• Cast vector<T> to vector<const T>

  - by user345386

  I have a member variable of type vector (where is T is a custom class, but it could be int as well.) I have a function from which I want to return a pointer to this vector, but I don't want the caller to be able to change the vector or it's items. So I want the return type to be const vector* None of the casting methods I tried worked. The compiler keeps complaining that T is not compatible with const T. Here's some code that demonstrates the gist of what I'm trying to do; vector<int> a; const vector<const int>* b = (const vector<const int>* ) (&a); This code doesn't compile for me. Thanks in advance!

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• Class basic operators

  - by swan

  Hi, Is it necessary to have a copy constructor, destructor and operator= in a class that have only static data member, no pointer class myClass{ int dm; public: myClass(){ dm = 1; } ~myClass(){ } // Is this line usefull ? myClass(const myClass& myObj){ // and that operator? this->dm = myObj.dm; } myClass& operator=(const myClass& myObj){ // and that one? if(this != &myObj){ this->dm = myObj.dm; } return *this; } }; I read that the compiler build one for us, so it is better to not have one (when we add a data member we have to update the operators)

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• Why do I have to give an identifier?

  - by Knowing me knowing you

  In code: try { System.out.print(fromClient.readLine()); } catch(IOException )//LINE 1 { System.err.println("Error while trying to read from Client"); } In code line marked as LINE 1 compiler forces me to give an identifier even though I'm not using it. Why this unnatural constrain? And then if I type an identifier I'm getting warning that identifier isn't used. It just doesn't make sense to me, forcing a programmer to do something unnecesarry and surplus. And after me someone will revise this code and will be wondering if I didn't use this variable on purpouse or I just forgot. So in order to avoid that I have to write additional comment explaining why I do not use variable which is unnecessary in my code. Thanks

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• F# function calling syntax confusion

  - by Daniel

  I have a piece of code: links |> Seq.map (fun x -> x.GetAttributeValue ("href", "no url")) Which I wanted to rewrite to: links |> Seq.map (fun x -> (x.GetAttributeValue "href" "no url")) But the F# compiler doesn't seem to like that. I was under the impression that these two function calls were interchangeable: f (a, b) (f a b) The error that I get is: The member or object constructor 'GetAttributeValue' taking 2 arguments are not accessible from this code location. All accessible versions of method 'GetAttributeValue' take 2 arguments. Which seems amusing, as it seems to indicate that it needs what I'm giving it. What am I missing here?

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• Best environment to port C/C++ code from Linux to Windows.

  - by Simone Margaritelli

  I'd like to make a big project of mine buildable on Windows platforms. The project itself it's written in C/C++ following POSIX standards, with some library dependencies such as libxml2, libcurl and so on. I'm more a Linux developer rather than a Windows developer, so i have no idea of which compiler suite i should use to port the code. Which one offers more compatibility with gcc 4.4.3 i'm using right now? My project needs flex and bison, is there any "ready to use" environment to port such projects to windows platforms? Thanks.

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• cygwin g++ produces no output

  - by fred basset

  I just installed g++ from cygwin, when I try to compile a C++ file I am not getting any executable produced by the compiler, see example below. What's going wrong? Directory of C:\helloworld 01/02/2011 04:50 PM . 01/02/2011 04:50 PM .. 01/02/2011 04:48 PM 94 helloworld.cpp 1 File(s) 94 bytes 2 Dir(s) 24,658,272,256 bytes free C:\helloworldg++-4 helloworld.cpp C:\helloworlddir Volume in drive C is OS Volume Serial Number is C47B-942D Directory of C:\helloworld 01/02/2011 04:50 PM . 01/02/2011 04:50 PM .. 01/02/2011 04:48 PM 94 helloworld.cpp 1 File(s) 94 bytes 2 Dir(s) 24,657,747,968 bytes free C:\helloworld

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• How to reference/link another project in grails workspace without using jar files?

  - by Ivan Alagenchev

  I have a Grails website that references a java core application. I have been successful in adding a .jar dependency to that project; however the java project is in the same workspace as my grails project and I would ultimately like to reference that project directly. I don't want to deal with the added step of creating a new jar file every time that there is a modification to the java project, cleaning and updating my dependencies. I added the java project to my grails' project "Java Build Path" and at first everything seemed to work fine, but when I run grailscompile, the compiler fails to resolve all imports that point to the java project. I am using Spring Source Toolsuite as my IDE.

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• TextAppearance_Holo_Large - No resource found

  - by npmaster

  When compiling my app I get the following error: android-apt-compiler: ... \res\values-v14\styles.xml:12: error: Error retrieving parent for item: No resource found that matches the given name '@android:style/TextAppearance_Holo_Large. The code it is complaining about is: <style name="Title" parent="@android:style/TextAppearance_Holo_Large"> <item name="android:layout_height">wrap_content</item> <item name="android:layout_width">wrap_content</item> </style> I checked my manifest file and I have set the SDK to: <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="17" /> Which i believe allows for using the Holo Themes. I am using Android Studio though I doubt that is the cause of the error. Any ideas what I am doing wrong?

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• How to explain to a developer that adding extra if - else if conditions is not a good way to "improv

  - by Lilit

  Recently I've bumped into the following C++ code: if (a) { f(); } else if (b) { f(); } else if (c) { f(); } Where a, b and c are all different conditions, and they are not very short. I tried to change the code to: if (a || b || c) { f(); } But the author opposed saying that my change will decrease readability of the code. I had two arguments: 1) You should not increase readability by replacing one branching statement with three (though I really doubt that it's possible to make code more readable by using else if instead of ||). 2) It's not the fastest code, and no compiler will optimize this. But my arguments did not convince him. What would you tell a programmer writing such a code? Do you think complex condition is an excuse for using else if instead of OR?

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• Hudson's FindBugs plugin reports line number "-1" for bugs. Ideas?

  - by John B.

  Greetings, I have a simple test project set up in Hudson and the project's build process (a batch file) generates a findbugs.xml file. This is processed by Hudson's FindBugs plugin but it shows the line number of the bugs as "-1" instead of their actual line number. A coworker suggested I enable debug info for the compiler. I used the -g "Generate all debugging info" option for javac but nothing seemed to change. My build command is: javac -g -classpath C:\testWebApp1\src -d C:\testWebApp1\build C:\testWebApp1\src\*.java The only other thing in the build.bat file is a call to the FindBug tool (text UI). Here is what the FindBugs Plugin says about the first bug: File: GenerateHellos.java, Line: -1, Type: UUF_UNUSED_FIELD, Priority: Normal, Category: PERFORMANCE Any ideas? Thanks a ton!

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