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• Is It Worth Using Bitwise Operators In Methods?

  - by user1626141

  I am very new to Java (and programming in general, my previous experience is with ActionScript 2.0 and some simple JavaScript), and I am working my way slowly and methodically through Java: A Beginner's Guide by Herbert Schildt. It is an incredible book. For one thing, I finally understand more-or-less what bitwise operators (which I first encountered in ActionScript 2.0) do, and that they are more efficient than other methods for certain sums. My question is, is it more efficient to use a method that uses, say, a shift right, to perform all your divisions/2 (or divisions/even) for you in a large program with many calculations (in this case, a sprawling RPG), or is it more efficient to simply use standard mathematical operations because the compiler will optimise it all for you? Or, am I asking the wrong question entirely?

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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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• 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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• Why Java cannot find my constructor?

  - by Roman

  Well, maybe it is a stupid question, but I cannot resolve this problem. In my ServiceBrowser class I have this line: ServiceResolver serviceResolver = new ServiceResolver(ifIndex, serviceName, regType, domain); And compiler complains about it. It says: cannot find symbol symbol : constructor ServiceResolver(int,java.lang.String,java.lang.String,java.lang.String) This is strange, because I do have a constructor in the ServiceResolver: public void ServiceResolver(int ifIndex, String serviceName, String regType, String domain) { this.ifIndex = ifIndex; this.serviceName = serviceName; this.regType = regType; this.domain = domain; } ADDED: I removed void from the constructor and it works! Why?

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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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• C pointer initialization and dereferencing, what's wrong here?

  - by randombits

  This should be super simple, but I'm not sure why the compiler is complaining here. #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { int *n = 5; printf ("n: %d", *n); exit(0); } Getting the following complaints: foo.c: In function ‘main’: foo.c:6: warning: initialization makes pointer from integer without a cast I just want to print the value that the pointer n references. I'm dereferencing it in the printf() statement and I get a segmentation fault. Compiling this with gcc -o foo foo.c.

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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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• In C#: How to declare a generic Dictionary whose key and value types have a common constraint type?

  - by Marcel

  Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: private IDictionary<T, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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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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• 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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• 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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• STL: how to overload operator= for <vector> ?

  - by MBes

  There's simple example: #include <vector> int main() { vector<int> veci; vector<double> vecd; for(int i = 0;i<10;++i){ veci.push_back(i); vecd.push_back(i); } vecd = veci; // <- THE PROBLEM } The thing I need to know is how to overload operator = so that I could make assignment like this: vector<double> = vector<int>; I've just tried a lot of ways, but always compiler has been returning errors... Is there any option to make this code work without changing it? I can write some additional lines, but can't edit or delete the existing ones. Ty.

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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 do XAML files associate with cs files?

  - by LLS

  It seems that XAML files should have corresponding .cs files in a C# project. I know Visual Studio does all the things for us. I'm just curious how they are linked together? I mean, are they specified in the project file, or just because they have the same names? And also, App.xaml file specifies the startup file, but how does the compiler know? Is it possible to appoint another file other than App.xaml to do the same things as App.xaml does?

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• Why is there "data" and "newtype" in Haskell?

  - by martingw

  To me it seems that a newtype definition is just a data definition that obeys some restrictions (only one constructor and such), and that due to these restrictions the runtime system can handle newtypes more efficiently. Ok, and the handling of pattern matching for undefined values is slightly different. But suppose Haskell would only knew data definitions, no newtypes: Couldn't the compiler find out for himself whether a given data definition obeys these restrictions, and automatically treat it more efficiently? I'm sure I'm missing out on something, these Haskell designers are so clever, there must be some deeper reason for this...

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• How to call 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. Linker is complaining about the unresolved symbols. 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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• 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 understand the programming of an operating system

  - by piemesons

  Hello, I want to learn the operating system. How it works. I don't want to make my own operating system. I just want to learn how it works. As I can find out source code of any open source OS. But how to start. Like starting from the first elementary kernel (whatever it is). Somebody suggested I try to implement Linux from scratch etc. Please guide me in a proper way. I want to know about the proper path to follow. I am ready to invest three to four years just to understand the basics. I have good fundamentals of C, C++, PHP, OOP and compiler design.

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• const member functions can call const member functions only?

  - by Abhi

  Hi all. Do const member functions call only const member functions? class Transmitter{ const static string msg; mutable int size; public: void xmit() const{ size = compute(); cout<<msg; } private: int compute() const{return 5;} }; string const Transmitter::msg = "beep"; int main(){ Transmitter t; t.xmit(); return EXIT_SUCCESS; } If i dont make compute() a const, then the compiler complains. Is it because since a const member function is not allowed to modify members, it wont allow any calls to non-consts since it would mean that the const member function would be 'indirectly' modifying the data members?

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• Reference to an instance method of a particular object

  - by Andrey

  In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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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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• 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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• 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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• C++ volatile required when spinning on boost::shared_ptr operator bool()?

  - by JaredC

  I have two threads referencing the same boost::shared_ptr: boost::shared_ptr<Widget> shared; On thread is spinning, waiting for the other thread to reset the boost::shared_ptr: while(shared) boost::thread::yield(); And at some point the other thread will call: shared.reset(); My question is whether or not I need to declare the shared pointer as volatile to prevent the compiler from optimizing the call to shared.operator bool() out of the loop and never detecting the change? I know that if I were simply looping on a variable, waiting for it to reach 0 I would need volatile, but I'm not sure if boost::shared_ptr is implemented in such a way that it is not necessary here.

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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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