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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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• 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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• iOS sdk question: how do I cast a UIView to a UIImage View (alternativly how do I get a UIImageView from a GestureRecognzer?)

  - by user439299

  Desired end result: user taps a UIImageView and the image changes to another image (a subsequent tap returns the image to the original state) Problem: I add a (unique) selector to a bunch of UIImageViews (in an array) and point the action at the same function - let's call this function imageTapped: for now. Here is my code so far: -(void)imageTapped:(UITapGestureRecognizer *)tapGesture { UIImageView *view = tapGesture.view; // rest of code... } This code actually works fine but gets a warning when I run it: "Incompatible objective c types initilizing 'struct UIView *', expected 'struct UIImageView *' Any way to get rid of this? Not sure how casting works in objective c... primitive types seem to work fine such as (int)someFloat works fine but (UIImageView)someUiView doesn't work. Like I said, code works alright when I run it but would like to get ride of the compiler warning. Any help would be awesome.... I am very new to objective c (or any non java language for that matter) so be gentle. Thanks in advance.

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• Rails: Duplicate functionality across controllers? A humble plea.

  - by Alex

  So I'm working with authlogic, and I'm trying to duplicate the login functionality to the welcome page, so that you can log in by restful url or by just going to the main page. No, I don't know if we'll keep that feature, but I want to test it out anyway. Here's the error message: RuntimeError in Welcome#index Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id The code is below. Basically, what's happening is the index view (the first code snippet) is sending the information from the form to the create method of user_sessions controller. At this point, in theory, it create should just pick up, but it doesn't. PLEASE help. Please. I've been doing this for about 8 hours. I checked Google. I checked IRC. I checked every book I could find. You don't even have to answer, I can to the grunt work if you just point me in the right direction. <% form_for @user_session, :url => user_sessions_path do |f| %> <%= f.text_field :email %><br /> <%= f.password_field :password %> <%= submit_tag 'Login' %> <% end %> class ApplicationController < ActionController::Base helper :all # include all helpers, all the time protect_from_forgery # See ActionController::RequestForgeryProtection for details # Scrub sensitive parameters from your log # filter_parameter_logging :password helper_method :current_user_session, :current_user before_filter :new_session_object protected def new_session_object unless current_user @user_session = UserSession.new(params[:user_session]) end end private def current_user_session return @current_user_session if defined?(@current_user_session) @current_user_session = UserSession.find end def current_user return @current_user if defined?(@current_user) @current_user = current_user_session && current_user_session.record end end

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• How do you specify a 64 bit unsigned int const 0x8000000000000000 in VS2008?

  - by Mark Franjione

  I read about the Microsoft specific suffix "i64" for integer constants. I want to do an UNsigned shift to a ULONGLONG. ULONGLONG bigNum64 = 0x800000000000000i64 >> myval; In normal C, I would use the suffix "U", e.g. the similar 32 bit operation would be ULONG bigNum32 = 0x80000000U >> myval; I do NOT want the 2's complement sign extension to propogate through the high bits. I want an UNSIGNED shift on a 64 bit const number. I think my first statement is going to do a SIGNED shift right. I tried 0x800000000000000i64U and 0x800000000000000u64 but got compiler errors.

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• How to check if TypeIdenitifier(T) is an Object?

  - by John

  I'm creating a generic list class that has a member of type Array(Array of ). The problem is the class descruction,because the class is supposed to be used for types from byte to types inheriting TObject. Specifically: destructor Destroy; var elem:T; begin /*if(T is Tobject) then //Check if T inherits TObject {Compiler error!} for elem in FData do TObject(elem).Free;*/ // do not know how to do it SetLength(FItems,0); //FItems : Array of T inherited Destroy; end; How do I check if T is TObject so I can free every member if the typeidenitifier is a class,for example?

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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 use replace_regex_copy() from boost::algorithm library?

  - by Vincenzo

  This is my code: #include <string> #include <boost/algorithm/string/regex.hpp> string f(const string& s) { using namespace boost::algorithm; return replace_regex_copy(s, "\\w", "?"); } This is what compiler says: no matching function for call to ‘replace_regex_copy(const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::string, std::string) The link to the library: http://www.boost.org/doc/libs/1_43_0/doc/html/boost/algorithm/replace_regex_copy.html Could anyone please help? Thanks! ps. Boost library is in place, since other functions from it work fine.

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• Can Visual Studio (should it be able to) compute a diff between any two changesets associated with a

  - by Hamish Grubijan

  Here is my use case: I start on a project XYZ, for which I create a work item, and I make frequent check-ins, easily 10-20 in total. ALL of the code changes will be code-read and code-reviewed. The change sets are not consecutive - other people check-in in-between my changes, although they are very unlikely to touch the exact same files. So ... at the en of the project I am interested in a "total diff" - as if there was a single check-in by me to complete the entire project. In theory this is computable. From the list of change sets associated with the work item, you get the list of all files that were affected. Then, the algorithm can aggregate individual diffs over each file and combine them into one. It is possible that a pure total diff is uncomputable due to the fact that someone else renamed files, or changed stuff around very closely, or in the same functions as me. I that case ... I suppose a total diff can include those changes by non-me as well, and warn me about the fact. I would find this very useful, but I do not know how to do t in practice. Can Visual Studio 2008/2010 (and/or TFS server) do it? Are there other source control systems capable of doing this? Thanks.

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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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• Pointer aliasing- in C++0x

  - by DeadMG

  I'm thinking about (just as an idea) disjointed pointer aliasing in C++0x. I was thinking about seeing if it could be implemented similarly to const correctness- that is, enforced by the compiler. What would be the requirements for such a thing? As this is more of a thought experiment, I'm perfectly happy to look at solutions that destroy legacy code or redefine half the language and that kind of thing. What I'd really rather not do is have, say, restrict from C99 where the programmer just promises it. It should be enforced.

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• Normal C++ code in Qt doesnt build and run

  - by Nick

  Hello. I am using Qt under linux, if it matters. I ran successfully under Geany (a simple c++ compiler) the following: //my first program in C++ Hello World! include using namespace std; int main () {cout << "Hello World!"; return 0;} I opened Qt source file and copied the exact same code and i can't build or run. Thank you for your responses to this simple problem.

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• Migrate from Oracle to MySQL

  - by Cassy

  Hi together. We ran into serious performance problems with our Oracle database and we would like to try to migrate to a MySQL-based database (either MySQL directly or, more preferrable, Infobright). The thing is, we need to let the old and the new system overlap for at least some weeks if not months, before we actually know, if all features of the new database match our needs. So, here is our situation: The Oracle database consists of multiple tables with each millions of rows. During the day, there are literally thousands of statements, which we cannot stop for migration. Every morning, new data is imported into the Oracle database, replacing some thousands of rows. Copying this process is not a problem, so we could, in theory, import in both databases in parallel. But, and here lies the challenge, for this to work, we need to have an export from the Oracle database with a consistent state from one day. (We cannot export some tables on Monday and some others on Tuesday, etc.) This means, that at least the export should be finished in less than one day. Our first thought was to dump the schema, but I wasn't able to find a tool to import an Oracle dump file into mysql. Exporting tables in CSV files might work, but I'm afraid it could take too long. So my question now is: What should I do? Is there any tool to import Oracle dump files into MySQL? Does anybody have any experience with such a large-scale migration? Thanks in advance, Cassy PS: Please, don't suggest performance optimization techniques for Oracle, we already tried a lot :-)

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• Can a method return an NSRange?

  - by Dan Donaldson

  I have a method that returns an NSRange. When I call this method from outside the class I get a compile error. NSRange tmpRange; tmpRange = [phrase rangeInString:searchString forString:theLetter goingForward:YES]; return tmpRange.location == -1; in the .h file: #import <Foundation/Foundation.h> @interface Phrase : NSObject { } - (NSRange) rangeInString:(NSString *) tgt forString:(NSString *) find goingForward:(BOOL) fwd; @end This method is called within the Phrase object by other methods without problems. The compiler says 'incompatible types in assignment'. Can anyone explain this to me? I assume it has to do with returning an NSRange/struct type value generated outside the object, but I don't know why it works in one place and not the other.

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• a macro question for c language (#define)

  - by Daniel

  I am reading source code of hoard memory allocator, and in the file of gnuwrapper.cpp, there are the following code #define CUSTOM_MALLOC(x) CUSTOM_PREFIX(malloc)(x) What's the meaning of CUSTOM_PREFIX(malloc)(x)? is CUSTOM_PREFIX a function? But as a function it didn't defined anywhere. If it's variable, then how can we use variable like var(malloc)(x)? more code: #ifndef __GNUC__ #error "This file requires the GNU compiler." #endif #include <string.h> #include <stdlib.h> #include <stdio.h> #include <malloc.h> #ifndef CUSTOM_PREFIX ==> here looks like it's a variable, so if it doesn't define, then define here. #define CUSTOM_PREFIX #endif #define CUSTOM_MALLOC(x) CUSTOM_PREFIX(malloc)(x) ===> what's the meaning of this? #define CUSTOM_FREE(x) CUSTOM_PREFIX(free)(x) #define CUSTOM_REALLOC(x,y) CUSTOM_PREFIX(realloc)(x,y) #define CUSTOM_MEMALIGN(x,y) CUSTOM_PREFIX(memalign)(x,y)

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• can a program written in C be faster than one written in OCaml and translated to C?

  - by Ole Jak

  So I have some cool Image Processing algorithm. I have written it in OCaml. It performs well. I now I can compile it as C code with such command ocamlc -output-obj -o foo.c foo.ml (I have a situation where I am not alowed to use OCaml compiler to bild my programm for my arcetecture, I can use only specialy modified gcc. so I will compile that programm with sometyhing like gcc -L/usr/lib/ocaml foo.c -lcamlrun -lm -lncurses and Itll run on my archetecture.) I want to know in general case can a program written in C be faster than one written in OCaml and translated to C?

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• Why can't I project ToString() in VB?

  - by Martinho Fernandes

  If you try to compile the query below in Visual Basic .NET, it fails. From x In {1, 2} Select x.ToString() The error given by the compiler is: Range variable name cannot match the name of a member of the 'Object' class. There is nothing wrong with the equivalent C# query, though: from x in new[]{1, 2} select x.ToString() This does not happen with the ToString overload that takes a format (it is a member of Int32, not Object). It does happen with other members of Object, as long as they don't take an argument: with GetType and GetHashCode it fails; with Equals(object) it compiles. Why is this restriction in place, and what alternatives can I use?

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• int vs const int&

  - by Valdo

  I've noticed that I usually use constant references as return values or arguments. I think the reason is that it works almost the same as using non-reference in the code. But it definitely takes more space and function declarations become longer. I'm OK with such code but I think some people my find it a bad programming style. What do you think? Is it worth writing const int& over int? I think it's optimized by the compiler anyway, so maybe I'm just wasting my time coding it, a?

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• Constructors in Inner classes (implementing Interfaces)

  - by thepandaatemyface

  Hi, How would I go about writing a constructor for an inner class which is implementing an interface? I know I could make a whole new class, but I figure there's got to be a way to do something along the line of this: JButton b = new JButton(new AbstractAction() { public AbstractAction() { super("This is a button"); } public void actionPerformed(ActionEvent e) { System.out.println("button clicked"); } }); When I enter this it doesn't recognize the AbstractAction method as a constructor (compiler asks for return type). Anyone have an idea? Thanks

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• Same memory space being allocated again & again

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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• Same memory space being allocated again & again while using malloc()

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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• Delegate Example From C# In Depth Confusion

  - by ChloeRadshaw

  I am looking at this example: List<Product> products = Product. GetSampleProducts() ; products.Sort( (first, second) => first.Name.CompareTo(second. Name) ) ; foreach (Product product in products) { Console. WriteLine(product) ; } What function is actually called in the API when you do that? Does the compiler create a class which implemnents the IComparer interface? I thought delegates were anonymous methods - Here it seems to be an anonymous interface implementation which is casuing confusion

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• Why I have to redeclare a virtual function while overriding [C++]

  - by Neeraj

  #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

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• Can I reproduce Scala's behavior for == ?

  - by JPP

  In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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• Calling C++ function from C.

  - by claws

  I know this. Calling C function from C++: If my application was in C++ and I had to call functions from a library written in C. Then I would have used //main.cpp extern "C" void C_library_function(int x, int y);//prototype C_library_function(2,4);// directly using it. This wouldn't mangle the name C_library_function and linker would find the same name in its input *.lib files and problem is solved. Calling C++ function from C??? But here I'm extending a large application which is written in C and I need to use a library which is written in C++. Name mangling of C++ is causing trouble here. Well I cannot use C++ compiler over my C project because thats breaking lot of other stuff. What is the way out? By the way I'm using MSVC

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