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• Visual Studio 2008 awful performance

  - by Nima

  Hi, I have ported a piece of C++ code, that works out of core, from Linux(Ubuntu) to Windows(Vista) and I realized that it works about 50times slower on VS2008! I removed all the out of core parts and now I just have a piece of code that has nothing to do with the hard disk. I set compiler parameters to O2 in Project Properties but still get about 10times slower than g++ in linux! Does anybody have an idea why it is this much slower under VS? I really appreciate any kind of hint! Thanks,

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• Compile-time trigonometry in C

  - by lhahne

  I currently have code that looks like while (very_long_loop) { ... y1 = getSomeValue(); ... x1 = y1*cos(PI/2); x2 = y2*cos(SOME_CONSTANT); ... outputValues(x1, x2, ...); } the obvious optimization would be to compute the cosines ahead-of-time. I could do this by filling an array with the values but I was wondering would it be possible to make the compiler compute these at compile-time?

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• Custom class object in Initialization list

  - by Michael

  I have a class Bar: class Bar { public: Bar(void); ~Bar(void); }; And a class Foo that gets a reference to Bar object as a constructor parameter and needs to save it in a private member bar_ : class Foo { private: Bar& bar_; public: Foo(Bar& bar) : bar_(bar) {} ~Foo(void) {} }; This doesn't compile : overloaded member function not found in 'Parser' missing type specifier - int assumed. Note: C++ does not support default-int Now i suspect couple of things that i need to assure, the second error is for Bar& bar_; declaration in Foo. Do i need to use an explicit constructor when declaring bar_ ? I am interested in learning how the compiler works regarding this matter, so a detailed explanation would be highly appreciated. Thanks.

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• How does c# type safety affect the garbage collection?

  - by Indeera

  I'm dealing with code that handles large buffers ( 100MB) and manipulation of these is done in unsafe blocks. I'd like to refactor these to avoid unsafe code. I'm wondering about the likely memory performance gains (positive/negative/neutral) before I embark on that. I assert that if the compiler can verify types, it could possibly generate better code and that could also mean good GC performance. Is this a valid assertion? What is your experience? Thanks.

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• error handling strategies in C?

  - by Leo

  Given the code below: typedef struct {int a;} test_t; arbitrary_t test_dosomething(test_t* test) { if (test == NULL) { //options: //1. print an error and let it crash //e.g. fprintf(stderr, "null ref at %s:%u", __FILE__, __LINE__); //2. stop the world //e.g. exit(1); //3. return (i.e. function does nothing) //4. attempt to re-init test } printf("%d", test->a); //do something w/ test } I want to get a compiler error if test is ever NULL, but I guess that's not possible in C. Since I need to do null checking at runtime, what option is the most proper way to handle it?

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• C++/CLI value class constraint won't compile. Why?

  - by Simon

  Hello, a few weeks ago a co-worker of mine spent about two hours finding out why this piece of C++/CLI code won't compile with Visual Studio 2008 (I just tested it with Visual Studio 2010... same story). public ref class Test { generic<class T> where T : value class void MyMethod(Nullable<T> nullable) { } }; The compiler says: Error 1 error C3214: 'T' : invalid type argument for generic parameter 'T' of generic 'System::Nullable', does not meet constraint 'System::ValueType ^' C:\Users\Simon\Desktop\Projektdokumentation\GridLayoutPanel\Generics\Generics.cpp 11 1 Generics Adding ValueType will make the code compile. public ref class Test { generic<class T> where T : value class, ValueType void MyMethod(Nullable<T> nullable) { } }; My question is now. Why? What is the difference between value class and ValueType?

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• Does Msbuild recognise any build configurations other than DEBUG|RELEASE

  - by Dean

  I created a configuration named Test via Visual Studio which currently just takes all of DEBUG settings, however I employ compiler conditions to determine some specific actions if the build happens to be TEST|DEBUG|RELEASE. However how can I get my MSBUILD script to detect the TEST configuration?? Currently I build <MSBuild Projects="@(SolutionsToBuild)" Properties="Configuration=$(Configuration);OutDir=$(BuildDir)\Builds\" /> Where @(SolutionsToBuild) is a my solution. In the Common MsBuild Project Properties it states that $(Configuration) is a common property but it always appears blank? Does this mean that it never gets set but is simply reserved for my use or that it can ONLY detect DEBUG|RELEASE. If so what is the point in allowing the creation of different build configurations?

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• How to free memory in try-catch blocks?

  - by Kra

  Hi, I have a simple question hopefully - how does one free memory which was allocated in the try block when the exception occurs? Consider the following code: try { char *heap = new char [50]; //let exception occur here delete[] heap; } catch (...) { cout << "Error, leaving function now"; //delete[] heap; doesn't work of course, heap is unknown to compiler return 1; } How can I free memory after the heap was allocated and exception occurred before calling delete[] heap? Is there a rule not to allocate memory on heap in these try .. catch blocks? Thanks

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• C++: Cannot convert from foo& to foo*

  - by Rosarch

  I have a method: odp(foo& bar); I'm trying to call it: foo baz; odp(&baz); I get a compiler error: error C2664: "odp" cannot convert parameter 1 from 'foo *' to 'foo &' What am I doing wrong? Aren't I passing in a reference to baz? UPDATE: Perhaps I have a misconception about the relationship between pointers and references. I thought that they were the same, except references couldn't be null. Is that incorrect?

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• Explicit initialization of struct/class members

  - by Zephon

  struct some_struct{ int a; }; some_struct n = {}; n.a will be 0 after this; I know this braces form of initialization is inherited from C and is supported for compatibility with C programs, but this only compiles with C++, not with the C compiler. I'm using Visual C++ 2005. In C this type of initialization struct some_struct n = {0}; is correct and will zero-initialize all members of a structure. Is the empty pair of braces form of initialization standard? I first saw this form of initialization in a WinAPI tutorial from msdn.

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• Passing a template func. as a func. ptr to an overloaded func. - is there a way to compile this code

  - by LoudNPossiblyRight

  Just a general c++ curiosity: This code below shouldn't compile because it's impossible to know which to instantiate: temp(const int&) or temp(const string&) when calling func(temp) - this part i know. What i would like to know is if there is anything i can do to the line marked PASSINGLINE to get the compiler to deduce that i want FPTR1 called and not FPTR2 ? #include<iostream> using std::cout; using std::endl; /*FPTR1*/ void func(void(*fptr)(const int&)){ fptr(1001001);} /*FPTR2*/ void func(void(*fptr)(const string&)){ fptr("1001001"); } template <typename T> void temp(const T &t){ cout << t << endl; } int main(){ /*PASSINGLINE*/ func(temp); return 0; } Thank you.

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• Can i have a negative value as constant expression in Scala?

  - by Klinke

  I have an Java-Annotation that return a double value: @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface DoubleValue { double value(); } When i try to attach the annotation to a field in a scala class and the value is negativ like here: class Test { @DoubleValue(-0.05) var a = _ } i get an compiler error with the message: "annotation argument needs to be a constant; found: 0.05.unary_-". I understood that i need a numerical literal and i looked into the Scala Language Specification and it seems, that the - sign is only used for the exponent but not for the mantissa. Does someone has an idea how i can have a negative value as runtime information using annotations? Thanks, Klinke

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• Parenthesis operator in C. What is the effect in the following code

  - by Andre

  Hi everyone, I was playing with a macro to enable/disable traces when I came out with the following code when the macro is disabled: int main { ("Hello world"); } This code is valid and I got the desired effect (nothing happens when the macro is disabled) but I couldn't figure out what exactly is happening. Is the compiler seeing the parenthesis as a "nameless" method declaration? To make it clearer the code is : #ifdef TRACE #define trace printf("%s %d -> ",__FILE__, __LINE__);printf else #define trace #endif int main { trace("Hello world"); } Thanks in advance.

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• Void in main and keeping Dos program from dying

  - by TimothyTech

  Alright, so im using bloodshed complier, first thing i should note is im using a 2001 edition C++ for the aboslute beginner, was there any changes to C++ since 2001 that would effect the validity of this book? i ask because i know php has php5 and now php6 but i havent seen any C++3. now for the reason i asked that, in this code it uses, void main (void) why would i want an arguement to be void? what does this do. But when i run the " void main (void) in my compiler it says that main must have a "int" before it. so i cant have "void" main (void); also, once the code runs through, as long as there isnt a "cin" the program closes. is this normal behavior, is there a better way to stop this besides making a cin at the end of my program.

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• Declaring a prototype of type "struct" - C

  - by Jamie Keeling

  I've been racking my brains on this for a while, I'm simply trying to create a method that returns a struct as I wish to return two int's. My prototype for the method is as follows: typedef struct RollDice(); Also the method itself: typedef struct RollDice() { diceData diceRoll; diceRoll.dice1 = 0; diceRoll.dice2 = 0; return diceRoll; } The compiler shows the error: "Syntax error: ')'" for both the prototype and actual method. The struct itself: typedef struct { int dice1; int dice2; }diceData; Is it obvious where I'm going wrong? I've tried everything I can think of. Thanks

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• xml to xsd to c# class - C# 3.0, .net 3.5

  - by uno

  Following this articlelink text one of the comments from 'zanoni' said he did it this way Using .NET 3.5: [XmlRoot] public class EmailConfiguration { [XmlElement] public string DataBoxID { get; set; } [XmlElement] public DefaultSendToAddressCollectionClass DefaultSendToAddressCollection { get; set; } } public class DefaultSendToAddressCollectionClass { [XmlElement] public string[] EmailAddress { get; set; } } How would I get my class to be as what he described? I ran the xsd tool and it is in the fashion as what shane posted in the above link [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "2.0.50727.3038")] [System.SerializableAttribute()] [System.Diagnostics.DebuggerStepThroughAttribute()] [System.ComponentModel.DesignerCategoryAttribute("code")] [System.Xml.Serialization.XmlTypeAttribute(AnonymousType=true)] [System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=false)] public partial class EmailConfiguration : object, System.ComponentModel.INotifyPropertyChanged { private string dataBoxIDField; private EmailConfigurationDefaultSendToAddressCollection[] defaultSendToAddressCollectionField; /// <remarks/> [System.Xml.Serialization.XmlElementAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified)] public string DataBoxID { get { return this.dataBoxIDField; } set { this.dataBoxIDField = value; this.RaisePropertyChanged("DataBoxID"); } }

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• Coping with weak typing

  - by John Leonard

  I'm a front end Flex developer peeking over the wall at html. One of the things I have a hard time with is weak typing in Javascript. I know many developers say they prefer it. How do I stop worrying and learn to love the weak typing? Are there best practices for variable naming that help make var types human readable? Another thing I have trouble with is getting by without my trusted compiler errors and warnings. I'm getting along with firebug. Is there anything else I should have in my toolkit?

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• Why do Java source files go into a directory structure?

  - by bdhar

  Suppose that I am creating a Java project with the following classes com.bharani.ClassOne com.bharani.ClassTwo com.bharani.helper.HelperOne com.bharani.helper.support.HelperTwo with files put immediately under the folder 'src' src/ClassOne.java src/ClassTwo.java src/HelperOne.java src/HelperTwo.java and compile them using the command $ javac src/*.java -d classes (assuming that classes directory exists) The compiler compiles these files and put the class files in appropriate sub-directories inside the 'classes' directory like this classes/com/bharani/ClassOne.class classes/com/bharani/ClassTwo.class classes/com/bharani/helper/HelperOne.class classes/com/bharani/helper/support/HelperTwo.class Because the spec mandates that the classes should go inside appropriate directory structure. Fine. My question is this: When I use an IDE such as Eclipse or NetBeans, they create the directory structure for the source code directory ('src' directory here) also. Why is that? Is it mandatory? Or, is it just a convention? Thanks.

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• how VAR is determined against many options?

  - by Royi Namir

  i have this code : IEnumerable<string> q = customers /*EF entity*/ .Select (c => c.Name.ToUpper()) .OrderBy (n => n) To select entity, ObjectContext actually create ObjectQuery, which implement IQueryable. The object return from ObjectQuery, is not normal object, but EntityObject but what if i write : ( notice the var) var q = customers /*EF entity*/ .Select (c => c.Name.ToUpper()) .OrderBy (n => n) it can be determined both to ienumerable or iqueryable : because ObjectQuery Also implements IEnumerable... i dont know if there's any specific info which tell the compiler "use A and not B. A is more specific..." ( there must be...i just cant find it) any help ? how will it know to use A || B ?

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• Key Value Observation (ala Cocoa) in GWT ?

  - by user179997

  Hi all, There are these 2 frameworks out there in the same "cloud application" space as GWT: Sproutcore and Cappuccino. Cappuccino is Cocoa for the web, Sproutcore is Cocoa-like and one very central idea in both is Key Value Observation where the framework itself provides the glue to change all dependencies of an object when it changes, and you only have to declare those dependencies. If that was too poorly expressed please see this presentation: http://www.infoq.com/presentations/subelsky-sproutcore-intro Since the pattern reduces the amount of code you type it reduces the number of bugs. Maybe it's too much to ask but I would like to have that and all the benefits of Eclipse/compiler that come with GWT. Is there support for this in GWT, or a library already developed? Or maybe there is support in some of the component libraries for GWT out there? Thanks

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• Why won't the debugger update?

  - by Tanner

  Hello everyone, Ive had this problem multiple times and it ruins my projects, I make some changes, like say I have a button in the top left corner of the form and move it to the top right corner, then I press debug but nothing happens to the form, it doesn't change the button is still in the top left-hand corner instead of the top right, and it also doesn't except any new code, its like it saved the project right there and won't move on. Does any one know why or had this problem before? Please, Help!!!! Additional Details: Compiler: Microsoft Visual C# 2008 Express Edition I once fixed this problem by rebuilding the solution, but its never worked again.

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• "Inherited" types in C++

  - by Ken Moynihan

  The following code does not compile. I get an error message: error C2039: 'Asub' : is not a member of 'C' Can someone help me to understand this? Tried VS2008 & 2010 compiler. template <class T> class B { typedef int Asub; public: void DoSomething(typename T::Asub it) { } }; class C : public B<C> { public: typedef int Asub; }; class A { public: typedef int Asub; }; int _tmain(int argc, _TCHAR* argv[]) { C theThing; theThing.DoSomething(C::Asub()); return 0; }

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• Maintaining a common set of Eclipse preferences

  - by Robert Munteanu

  Whenever I switch workspaces/Eclipse installs I need to copy/redo the preferences: compiler settings; font sizes/families; code formatter; java code templates; editor templates; code clean-ups; I would like to maintain these settings in an unitary way, preferrably under source control. How can I do that? I know about 'copy settings' when creating a new workspace, but it does not keep updated copies.

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• Does a static object within a function introduce a potential race condition?

  - by Jeremy Friesner

  I'm curious about the following code: class MyClass { public: MyClass() : _myArray(new int[1024]) {} ~MyClass() {delete [] _myArray;} private: int * _myArray; }; // This function may be called by different threads in an unsynchronized manner void MyFunction() { static const MyClass _myClassObject; [...] } Is there a possible race condition in the above code? Specifically, is the compiler likely to generate code equivalent to the following, "behind the scenes"? void MyFunction() { static bool _myClassObjectInitialized = false; if (_myClassObjectInitialized == false) { _myClassObjectInitialized = true; _myClassObject.MyClass(); // call constructor to set up object } [...] } ... in which case, if two threads were to call MyFunction() nearly-simultaneously, then _myArray might get allocated twice, causing a memory leak? Or is this handled correctly somehow?

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• why make said no rule to make target

  - by guilin ??

  Isn't Makefile syntax is target: require_files cmd... Why I got this problem? Makefile MXMLC = /opt/flex/bin/mxmlc MXMLC_RELEASE = $(MXMLC) -debug=false -compiler.optimize=true release: bin-release/Wrapper.swf, bin-release/Application.swf bin-release/Application.swf: src/**/*.as, lib/*.swc $(MXMLC_RELEASE) -output bin-release/Application.swf src/Application.as @@-rm ../server/public/game/Application.swf $(CP) bin-release/Application.swf ../server/public/game/Application.swf bin-release/Wrapper.swf: src/*.as, src/engine/**/*.as, lib/*.swc $(MXMLC_RELEASE) -output bin-release/Wrapper.swf src/Wrapper.as @@-rm ../server/public/game/Wrapper.swf $(CP) bin-release/Wrapper.swf ../server/public/game/Wrapper.swf $: make bin-release/Application.swf ~/workspace/project/src/flash [2]19:20 make: * No rule to make target src/constant/*.as,', needed bybin-release/Application.swf'. Stop.

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