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  • Query on the scope of local variables in C

    - by darkie15
    All, Consider the following code: void func(void) { int a; printf ("%d", a); } int main(int argc, char **argv) { int a = 3; func(); printf("%d", a); } According to my understanding, the output should be: <junk value><3> Can anyone please confirm my understanding? My basic query is, does the compiler refer to the outer scope for a variable that has been declared but not defined? Regards, darkie

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  • C++/g++: Concurrent programm

    - by phimuemue
    Hi, I got a C++ program (source) that is said to work in parallel. However, if I compile it (I am using Ubuntu 10.04 and g++ 4.4.3) with g++ and run it, one of my two CPU cores gets full load while the other is doing "nothing". So I spoke to the one who gave me the program. I was told that I had to set specific flags for g++ in order to get the program compiled for 2 CPU cores. However, if I look at the code I'm not able to find any lines that point to parallelism. So I have two questions: Are there any C++-intrinsics for multithreaded applications, i.e. is it possible to write parallel code without any extra libraries (because I did not find any non-standard libraries included)? Is it true that there are indeed flags for g++ that tell the compiler to compile the program for 2 CPU cores and to compile it so it runs in parallel (and if: what are they)?

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  • Will Windows Update modify anything in Visual Studio?

    - by Martin
    (Note: Yes, the technical side of this question seems to be rather SuperUser, but the implications are more relevant for StackOverflow readers.) As the title says, we are wondering if (fully) enabling automated Windows Updates on our developer machines will have implications for MS Visual Studio. That is, will any fixes to any components (be it libraries, UI/IDE, compiler, ...) ever be updated through Windows Update? We want to have 100% exact and reproducible development environments (wrt C++) on all developer machines, and so we are concerned that automated Windows updates may introduce some uncontrolled updates into our development chain.

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  • sequentially-consistent atomic load on x86

    - by axe
    Hello all, I'm interested in sequentially-consistent load operation on x86. As far as I see from assembler listing, generated by compiler it is implemented as a plain load on x86, however plain loads as far as I know guaranteed to have acquire semantics, while plain stores are guaranteed to have release. Sequentially-consistent store is implemented as locked xchg, while load as plain load. That sounds strange to me, could you please explain this in details? added Just found in internet, that sequentially-consistent atomic load could be done as simple mov as long as store is done with locked xchg, but there was no prove and no links to documentation. Do you know where can I read about that? Thanks in advance.

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  • What's the best way to build software that doesn't require the newest glibc?

    - by ZorbaTHut
    I'm attempting to build a binary package that can be run on multiple Linux distributions. It's currently built on Ubuntu 10.04, but it fails on Ubuntu 8.04 with the following error: ./test: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.11' not found (required by ./test) ./test: /usr/lib/libstdc.so.6: version `GLIBC_2.11' not found (required by ./test) What's the preferred way to solve this problem? Is there a way to install an old glibc on a new box and build against it, or do I have to build on an old distribution? And if I build against an old glibc, will it work on a new glibc? Or, alternatively, are there just some handy compiler flags or packages I could install to solve the problem?

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  • ToList()-- Does it Create a New List?

    - by Ngu Soon Hui
    Let's say I have a class public class MyObject { public int SimpleInt{get;set;} } And I have a List<MyObject>, and I ToList() it and then change one of the SimpleInt, will my change be propagated back to the original list. In other words, what would be the output of the following method? public void RunChangeList() { var objs = new List<MyObject>(){new MyObject(){SimpleInt=0}}; var whatInt = ChangeToList(objs ); } public int ChangeToList(List<MyObject> objects) { var objectList = objects.ToList(); objectList[0].SimpleInt=5; return objects[0].SimpleInt; } Why? P/S: I'm sorry if it seems obvious to find out. But I don't have compiler with me now...

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  • floats in NSArray

    - by JordanC
    I have an NSArray of floats which I did by encapsulating the floats using [NSNumber numberWithFloat:myFloat] ; Then I passed that array somewhere else and I need to pull those floats out of the array and perform basic arithmatic. When I try [myArray objectAtIndex:i] ; The compiler complains that I'm trying to perform arithmatic on a type id. It also won't let me cast to float or double. Any ideas? This seems like it should be an easy problem. Maybe it will come to me after another cup of coffee, but some help would be appreciated. Thanks.

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  • How to avoid "incomplete implementation" warning in partial base class

    - by garph0
    I have created a protocol that my classes need to implement, and then factored out some common functionality into a base class, so I did this: @protocol MyProtocol - (void) foo; - (void) bar; @end @interface Base <MyProtocol> @end @interface Derived_1 : Base @end @interface Derived_2 : Base @end @implementation Base - (void) foo{ //something foo } @end @implementation Derived_1 - (void) bar{ //something bar 1 } @end @implementation Derived_2 - (void) bar{ //something bar 2 } @end In this way in my code I use a generic id<MyProtocol>. The code works (as long as Base is not used directly) but the compiler chokes at the end of the implementation of Base with a warning: Incomplete implementation of class Base Is there a way to avoid this warning or, even better, a more proper way to obtain this partially implemented abstract base class behavior in Objc?

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  • Question about inserting assembly code in C++

    - by Bruce
    I am working on VC++ compiler. I want to accomplish the following The variables s.AddrFrame.Offset and s.AddrStack.Offset contain the value of EBP and ESP respectively. I want to extract the value of old EBP and the return address. Assuming the address EBP + 1 contains the old 32 bit EBP value and EBP + 5 the return address I wrote the following code: unsigned int old_ebp = 0; unsigned int ret_addr = 0; __asm{ mov old_ebp, DWORD PTR [s.AddrFrame.Offset + 1] mov ret_addr, DWORD PTR [s.AddrStack.Offset + 5] } But this is not compiling xxxx.cpp(1130) : error C2415: improper operand type Please Help

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  • very simple delegate musing

    - by Ted
    Sometimes the simplest questions make me love C/C++ and C# more and more. Today sitting on the bus musing aout delegates I remembered reading somwhere you don't need to use the new keyword when instaniating a new delegate. For example: public static void SomeMethod(string message) { ... } ... public delegate void TestDelgate(string message); //Define a delegate ........... //create a new instance ..METHOD 1 TestDelgate t = new TestDelgate(SomeMethod); //OR another way to create a new instance ..METHOD 2 TestDelgate t = SomeMethod; //create a new instance ..METHOD 2 So todays questions are What happens under the hood in method 2. Does the compiler expand method 2 into method 1, hence writing TestDelgate t = SomeMethod; is just a shortcut for TestDelgate t = new TestDelgate(SomeMethod);, or is there another reason for the exsitence of method 2 Do you guys think method 1 or method 2 is better for readability (this is a subjective question, but I'd just like to get a unscientific feel of general opinion of stackoverflow :-))

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  • Is It Safe to Cast Away volatile?

    - by Yan Cheng CHEOK
    Most of the time, I am doing this way. class a { public: ~ a() { i = 100; // OK delete (int *)j; // Compiler happy. But, is it safe? // Error : delete j; } private: volatile int i; volatile int *j; }; int main() { a aa; } However, I saw an article here: https://www.securecoding.cert.org/confluence/display/seccode/EXP32-C.+Do+not+access+a+volatile+object+through+a+non-volatile+reference Casting away volatile allows access to an object through a non-volatile reference. This can result in undefined and perhaps unintended program behavior. So, what will be the workaround for my above code example?

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  • Will TFS 2010 support non-contiguous merging?

    - by steve_d
    I know that merging non-contiguous changesets at once may not be a good idea. However there is at least one situation in which merging non-contiguous changesets is (probably) not going to break anything: when there are no intervening changes on the affected individual files. (At least, it wouldn't break any worse than would a series of cherry-picked merges, checked in each time; and at least this way you would discover breakage before checking in). For instance, let's say you have a Main and a Development branch. They start out identical (e.g. after a release). They have two files, foo.cs and bar.cs. Alice makes a change in Development\foo.cs and checks it in as changeset #1001. Bob makes a change in Development\bar.cs and checks it in as #1002. Alice makes another change to Development\foo.cs and checks it in as #1003. Now we could in theory merge both changes #1001 and #1003 from dev-to main in a single operation. If we try to merge at the branch level, dev-to-main, we will have to do it as two operations. In this simple, contrived example it's simple enough to merge the one file - but in the real world where there would be many files involved, it's not so simple. Non-contiguous merging is one of the reasons given for why "merge by workitem" is not implemented in TFS.

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  • Prevent Erroneous Property Assignment

    - by Gordon
    Porting android applications to iphone applications always gives me the following pattern that I accidentally create: - (void) myFunc:(id)prop { self.property = property; } Which instead should be: - (void) myFunc:(id)prop { self.property = prop; } This always causes my program to quietly break because property gets reset to its existing value rather than being set to the new value, 'prop'. I cannot name the parameter 'prop' to 'property' since the compile complains that the parameter masks the instance variables visibility. Is there a good way to avoid this situation? There are no compiler warnings. Is there a way to make xcode prevent this? I cannot see very many situations where you would set a property to the value of its underlying instance variable (maybe to trigger a KVO binding?), but I don't see myself doing that in majority of cases. I understand the above code is synthetic and should be done with @synthesize, but I am just using it as a simplified example to illustrate my point.

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  • What could possibly cause this error(when declaring an object inside a class) ? //noobie question

    - by M4design
    I'm battling with this assignment :) I've got two classes: Ocean and Grid. When I declare an object of the Grid inside the Ocean: unsigned int sharkCount; Grid grid; The compiler/complainer says: error C2146: syntax error : missing ';' before identifier 'grid' Can you possibly predict what produces this error with the limited info' I provided? It seems that as if the Ocean doesn't like the Grid class. Could this be because of the poor implementation of the grid class. BTW the Grid has a default constructor. Yet the error happens in compiling time!. Thanks. EDIT: They're each in separate header file, and I've included the Grid.h in the Ocean.h.

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  • Output Unicode to Console Using C++

    - by Jesse Foley
    I'm still learning C++, so bear with me and my sloppy code. The compiler I use is Dev C++. I want to be able to output Unicode characters to the Console using cout. Whenver i try things like: # #include directive here (include iostream) using namespace std; int main() { cout << "Hello World!\n"; cout << "Blah blah blah some gibberish unicode: ÐAßGg\n"; system("PAUSE"); return 0; } It outputs strange characters to the console, like µA¦Gg. Why does it do that, and how can i get to to display ÐAßGg? Or is this not possible with Windows?

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  • Array::ConvertAll in managed C++

    - by danny.lesnik
    This is a continuation from this post. I'm trying to parse this string in managed C++: String ^ rgba = "[0.09019608,0.5176471,0.9058824,1]"; cli::array<System::Double> ^ RGB = System::Array::ConvertAll<String,cli::array<System::Double> >((rgba->Substring(1,rgba->Length-2)->Split(',')),double::Parse); Compiler throws me the following error: Error 15 error C2770: invalid explicit generic argument(s) for 'cli::array<Type,dimension> ^System::Array::ConvertAll(cli::array<TInput,1> ^,System::Converter<TInput,TOutput> ^)' What am I doing wrong?

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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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  • struct constructor + function parameter

    - by Oops
    Hi, I am a C++ beginner. I have the following code, the reult is not what I expect. The question is why, resp. what is wrong. For sure, the most of you see it at the first glance. struct Complex { float imag; float real; Complex( float i, float r) { imag = i; real = r; } Complex( float r) { Complex(0, r); } std::string str() { std::ostringstream s; s << "imag: " << imag << " | real: " << real << std::endl; return s.str(); } }; class Complexes { std::vector<Complex> * _complexes; public: Complexes(){ _complexes = new std::vector<Complex>; } void Add( Complex elem ) { _complexes->push_back( elem ); } std::string str( int index ) { std::ostringstream oss; Complex c = _complexes->at(index); oss << c.str(); return oss.str(); } }; int main(){ Complexes * cs = new Complexes(); //cs->Add(123.4f); cs->Add(Complex(123.4f)); std::cout << cs->str(0); return 0; } for now I am interested in the basics of c++ not in the complexnumber theory ;-) it would be nice if the "Add" function does also accept one real (without an extra overloading) instead of only a Complex-object is this possible? many thanks in advance Oops

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  • Strange exception phenomenon in Windows 7

    - by Level 2
    I spot some interesting articles about exception handle in CodeProject http://www.codeproject.com/KB/cpp/seexception.aspx After reading, I decided to do some experiment. The first time I try to execute the following code char *p; p[0] = 0; The program died without question. But After several times when I executed the same problem binary code, it magically did fine. Even the following code is doing well. Any clue or explanation? char *p p[1000] = 'd'; cout<<p[1000]<<endl; My O/S is Windows 7 64bit and compiler is VS2008 rc1.

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  • initialization of objects in c++

    - by Happy Mittal
    I want to know, in c++, when does the initialization of objects take place? Is it at the compile time or link time? For ex: //file1.cpp extern int i; int j=5; //file2.cpp ( link with file1.cpp) extern j; int i=10; Now, what does compiler do : according to me, it allocates storage for variables. Now I want to know : does it also put initialization value in that storage or is it done at link time?

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  • Iterate Through JSON Data for Specific Element - Similar to XPath

    - by Highroller
    I am working on an embedded system and my theory of the overall process follows this methodology: 1. Send a command to the back end asking for account information in JSON format. 2. The back end writes a JSON file with all accounts and associated information (there could be 0 to 16 accounts). 3. Here's where I get stuck - use JavaScript (we are using the JQuery library) to iterate through the returned information for a specific element (similar to XPath) and build an array based on the number of elements found to populate a drop-down box to select the account you want to view and then do stuff with the account info. So my code looks like this: loadAccounts = function() { $.getJSON('/info?q=voip.accounts[]', function(result) { var sipAcnts = $("#sipacnts"); $(sipAcnts).empty(); // empty the dropdown (if necessarry) // Get the 'label' element and stick it in an array // build the array and append it to the sipAcnts dropdown // use array index to ref the accounts info and do stuff with it } So what I need is the JSON version of XPath to build the array of voip.accounts.label. The first account info looks something like this: { "result_set": { "voip.accounts[0]": { "label": "Dispatch1", "enabled": true, "user": "1234", "name": "Jane Doe", "type": "sip", "sip": { "lots and lots of stuff": }, } } } Am I over complicating the issue? Any wisdom anyone could thrown down would be greatly appreciated.

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  • Is it legal for a C++ reference to be NULL?

    - by BCS
    A while back I ran into a bug the looked something like this: void fn(int &i) { printf(&i == NULL ? "NULL\n" : "!NULL\n"); } int main() { int i; int *ip = NULL; fn(i); // prints !NULL fn(*ip); // prints NULL return 0; } More recently, I ran into this comment about C++ references: [References arguments make] it clear, unlike with pointers, that NULL is not a possible value. But, as show above, NULL is a possible value. So where is the error? In the language spec? (Unlikely.) Is the compiler in error for allowing that? Is that coding guide in error (or a little ambiguous)? Or am I just wandering into the minefield known as undefined behavior?

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  • Help Me: Loading Qt dialogs from python Scripts

    - by krishnanunni
    Hello, im a novice into developing an application using backend as Python (2.5) and Qt(3) as front end GUI designer. I have 5 diffrent dialogs to implement the scripts. i just know to load the window (main window) from qt import * from dialogselectkernelfile import * from formcopyextract import * import sys if __name__ == "__main__": app = QApplication(sys.argv) f = DialogSelectKernelFile() f.show() app.setMainWidget(f) app.exec_loop() main dialog opens on running. i have a set of back,Next,Cancel buttons pusing on each should open the next or previous dialogs. i use the pyuic compiler to source translation.how can i do this from python. please reply i`m running out of time.i dont know how to load another dialog from a signal of push button in another dialog. Help me pls Thanks a Lot

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  • How to reliably specialize template with intptr_t in 32 and 64 bit environments?

    - by vava
    I have a template I want to specialize with two int types, one of them plain old int and another one is intptr_t. On 64 bit platform they have different sizes and I can do that with ease but on 32 bit both types are the same and compiler throws an error about redefinition. What can I do to fix it except for disabling one of definitions off with preprocessor? Some code as an example: template<typename T> type * convert(); template<> type * convert<int>() { return getProperIntType(sizeof(int)); } template<> type * convert<intptr_t>() { return getProperIntType(sizeof(intptr_t)); } //this template can be specialized with non-integral types as well, // so I can't just use sizeof() as template parameter. template<> type * convert<void>() { return getProperVoidType(); }

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  • ASP.NET MVC4: How to convert an IEnumerable to a string for ViewBag

    - by sehummel
    This is what I'm trying to do, but it doesn't work: HardwareType hwt = new HardwareType { HType = "PC" }; IEnumerable<Hardware> Pcs = db.Hardware.Where(h => h.HardwareType.Contains(hwt)); ViewBag.Pcs = Pcs.ToString(); So how do I convert my IEnumerable to a string (or other primitive data type) so the compiler won't give me an error when I try to use it in my Razor? @foreach (var item in ViewBag.Pcs) { <li><a href="#" class="btn"><i class="icon-hdd"></i> @item.HType</a></li> }

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