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  • How to implement a private virtual function within derived classes?

    - by Dane
    Hi, I know why I want to use private virtual functions, but how exactly can I implement them? For example: class Base{ [...] private: virtual void func() = 0; [...] } class Derived1: puplic Base{ void func() { //short implementation is ok here } } class Derived2: puplic Base{ void func(); //long implementation elsewhere (in cpp file) } [...] void Derived2::func() { //long implementation } The first version is ok but not always possible. Isn't the second version simply name hiding? How do you define the Base::func() of Derived2, if you cannot do it within the class declaration of Dereived2? Thanks

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  • Forward declaring an enum in c++

    - by szevvy
    Hi guys, I'm trying to do something like the following: enum E; void Foo(E e); enum E {A, B, C}; which the compiler rejects. I've had a quick look on Google and the consensus seems to be "you can't do it", but I can't understand why. Can anyone explain? Many thanks. Clarification 2: I'm doing this as I have private methods in a class that take said enum, and I do not want the enum's values exposed - so, for example, I do not want anyone to know that E is defined as enum E { FUNCTIONALITY_NORMAL, FUNCTIONALITY_RESTRICTED, FUNCTIONALITY_FOR_PROJECT_X } as project X is not something I want my users to know about. So, I wanted to forward declare the enum so I could put the private methods in the header file, declare the enum internally in the cpp, and distribute the built library file and header to people. As for the compiler - it's GCC.

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  • C++ Virtual keyword as away to avoid including code units.

    - by user394663
    Currently we have a body of code that allows service plugins which offer forms of communication to the core e.g tcp/ip, udp/ip, usb, etc... These service plugins feedback notifier class instances to the core for further processing. In the current implementation a service project (which is a separate dynamically linked library brought in at runtime by the core via dlopen and friends) will compile against the notifier.cpp file that resides in the core source code (a separate project). This gives access to the notifiers method implementations. This works perfectly no complaints. Two alternative options: 1. put the notifier method implementations in the header file. 2. declare the notifier methods virtual and delay binding until runtime. Avoiding the issues of computational overhead what are the impacts of option 2? Are there any other options available to us? Thanks

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  • c++: use a #define in printf?

    - by John
    I was wanting to use a constant of some kind for the application ID (so I can use it in printf). I had this: #define _APPID_ "Hello World!" And then the simple printf, calling it into %s (string). It put this out: simple.cpp:32: error: cannot convert ‘_IO_FILE*’ to ‘const char*’ for argument ‘1’ to ‘int printf(const char*, ...)’ What would I use to define the application ID to use in printf? I tried: static const char _APPID_[] = "Hello World"` but it didn't work, same error I think.

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  • Visual C++ 9 Linker file size limitation.

    - by Raindog
    It appears that the visual C++ 9 linker has a file allocation algorithm that doubles the size of the file every allocation, so you get 512mb, 1024mb, 2048mb, 4096mb. The problem is that it is using a library that cannot handle files larger 2048MB, and as such crashes with an error such as "cannot read file at is the disk full or write protected". Is there a way to bypass this limitation or otherwise replace the linker with something else that works? A bit of background, I have a code generator that generates a large number of files, ~15k cpp files, I've managed to reduce the number of files to something about 6k to get something that at least completes the linking process, I would like to be able to include all 15k without having to create multiple libs.

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  • [Qt] How to make another window pop up that extends QWidget as opposed to QDialog?

    - by Graphics Noob
    So far I've only had my main window pop up other windows that were QDialogs and I'm not getting it to work with a QWidget. The other window I want to display was designed with the Form Editor, then wrapped in a class called ResultViewer which extends QWidget (as opposed to QDialog). What I want is to have the ResultViewer show its ui in a seperate window. Now when I try to display it the ResultViewer ui just pops up in the main window on top of the mainwindow ui. The code I'm using to display it is this (in my mainwindow.cpp file) ResultViewer * rv = new ResultView(this); rv->show(); The constructor for the ResultViewer looks like this ResultViewer::ResultViewer(QWidget * parent) : QWidget(parent), ui(new Ui::ResultViewer) { ui->setupUi(this); } I've looked through the QWidget documentation a bit but the only thing I can find that may be related is the QWidget::window() function, but the explanation isn't very clear, it just gives an example of changing the title of a window.

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  • strenge exception phenomenon in win7

    - by Level 2
    Hello all, I spot some interesting artcles 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 excute the following code char *p; p[0] = 0; The program died without question. But After serveral time I execute the same problem binary code. It magically did fine. even the following code is doing well. any clue or explain? char *p p[1000] = 'd'; cout<<p[1000]<<endl; my os is windows 7 64bit and compiler is vs2008 rc1.

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  • Implementing a client for ActiveMQ events

    - by recipriversexclusion
    I can listen to events from a certain topic in an ActiveMQ server using a simple asynchronous listener and print the incoming events to the console (code to that actually comes as an example in the activemq-cpp library). I would like to create clients on other machines that will listen to these events and update their displays. My question is: how to best go about doing this? Are there any Ajax examples you can point me that implement similar functionality? Or is there another technology (comet?) that is better to use for this scenario? How can I display the events in teh browser window as they are received by the client, should I use JQuery?

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  • What does this C++ code mean

    - by Markus Orreilly
    I was trying to understand how webkit parses urls, and I'm having a hard time making heads or tails of this: Vector<char, 4096> buffer(fragmentEnd * 3 + 1); This line is on line 1214 (you can see it here: http://trac.webkit.org/browser/trunk/WebCore/platform/KURL.cpp#L1214). I get that it's making a vector of type char, with each entry being an array of char 4096 bytes large, but I don't get the buffer(fragmentEnd * 3 + 1) part. I think that it confuses me most b/c I can't find where the buffer variable is instantiated anywhere (shouldn't it be something more like Vector<char, 4096> buffer = new Vector<char, 4096>(...)? Thanks in advance

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  • c++ when to put method out side the class

    - by user63898
    i saw that some times in c++ applications using only namespace declarations with header and source file like this : #ifndef _UT_ #define _UT_ #include <string> #include <windows.h> namespace UT { void setRootPath(char* program_path, char* file_path); char * ConvertStringToCharP(std::string str); }; #endif //and then in UT.cpp #include "UT.h" namespace UT { char * ConvertStringToCharP(std::string str) { char * writable = new char[str.size() + 1]; std::copy(str.begin(), str.end(), writable); writable[str.size()] = '\0'; return writable; } void setRootPath(char* program_path, char* file_path) { //... } } is it better then defining classic class with static methods? or just simple class ? dose this method has something better for the compiler linker ? the methods in this namespace are called allot of times .

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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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  • simple c++ file opening issue

    - by Robert
    #include <iostream> #include <fstream> using namespace std; int main () { ofstream testfile; testfile.open ("test.txt"); testfile << "success!\n"; testfile.close(); return 0; } 1)called "g++ testfile.cpp" 2)created "test.txt" 3)called "chmod u+x a.out" 4)??? 5)file remains blank. I feel like an idiot for failing at something as trivial as this is supposed to be.

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  • [c++] Resolving namespace conflicts

    - by Kyle
    I've got a namespace with a ton of symbols I use, but I want to overwrite one of them: external_library.h namespace lottaStuff { class LotsOfClasses {}; class OneMoreClass {}; }; my_file.h using namespace lottaStuff; namespace myCustomizations { class OneMoreClass {}; }; my_file.cpp using myCustomizations::OneMoreClass; int main() { OneMoreClass foo; // error: reference to 'OneMoreClass' is ambiguous return 0; } How do I get resolve the 'ambiguous' error without resorting to replacing 'using namespace lottaStuff' with a thousand individual "using xxx;" statements?

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  • use file or class for documenting classes in doxygen?

    - by AlejandroVK
    Hi all, This surely is a noob question, but I can't find an answer in Doxygen documentation. I'm not sure whether using: @file or @class when documenting my header files. The reason is that if I put file, then all the comments appear in the Files tab only, but not in the Classes tab (per each). For cpp it's ok, I just use file and it's good, but if I use both file and class in the header (file at the beginning and class right before the start of the class declaration) then I get duplicated entries for the class in the generated documentation... What I'm doing wrong? Any suggestions? Ideas? Regards, Alex

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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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  • Lib Files and Defines

    - by Paul
    I'm using a couple of external libraries and I'd rather not have to include all their source and header files in my main source directory or in my project file. One option would be to compile the libraries as lib files and link them like that. However I'm not sure the defines get evaluated before or after the lib file gets created (which one is it?). If it's before then obviously I can't just pack them because they might not work properly on different compilers or systems. So if I can't pack the libraries as lib files, is there any way for me to link in the c or cpp source files? Probably not, since they would have to be compiled first, but maybe I'm wrong. Edit: Here's a follow-up question, based on answers. Do you think it'd be too much of a hassle to have a makefile that creates the lib files? I'd still rather not add the sources to my project or in my source directory.

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  • Freeing memory with Pointer Arithmetic

    - by Breedly
    C++ newb here. I'm trying to write my own implementation of an array using only pointers, and I've hit a wall I don't know how to get over. My constructor throws this error array.cpp:40:35: error: invalid conversion from ‘int*’ to ‘int’ [-fpermissive] When my array initializes I want it to free up all the spaces in the array for ints. Array::Array(int theSize){ size = theSize; int *arrayPointer = new int; int index = 0; while(theSize > index){ *(arrayPointer + index) = new int; //This is the trouble line. ++index; } } What am I doing wrong stackoverflow?

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  • Preventing objects from being linked if they are not needed?

    - by Massif
    I have an ARM project that I'm building with make. I'm creating the list of object files to link based on the names of all of the .c and .cpp files in my source directory. However, I would like to exclude objects from being linked if they are never used. Will the linker exclude these objects from the .elf file automatically even if I include them in the list of objects to link? If not, is there a way to generate a list of only the objects that need to be linked?

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  • Oh no, Not another Undefined Reference Question!

    - by roony
    Unfortunately yes. I have my shared library compiled, the linker doesn't complain about not finding it but still I get undefined reference error. Thinking that I might be doing something wrong I did a little research and found this nice, simple walkthrough: http://www.adp-gmbh.ch/cpp/gcc/create_lib.html which I've followed to the letter but still I get: $ gcc -Wall main.c -o dynamically_linked -L.\ -lmean /tmp/ccZjkkkl.o: In function `main': main.c:(.text+0x42): undefined reference to `mean' collect2: ld returned 1 exit status This is pretty simple stuff so what's going wrong?!?!? Can anyone suggest something in my set up that might need checking/tweeking? GCC 4.3.2 Fedora 10 64-bit

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  • Understanding c++ block of code

    - by kotoko
    I was given a c++ main and have to code it so it works. I am having some trouble understanding the code as I am a bit new to cpp. Here is the code int main(int argc, char *argv[]) { Class::setAtribute("string"); Class(Class::CONSTANT) << "starting up..."; } Some questions: How can the first line work with no variables? Is it static? The second line is really strange for me, what I can make out is a Constructor that takes in a class constante and then prints it out somehow? If someone could explain me this bit of code it would be great! Thanks in advance.

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  • Linkage of namespace functions

    - by user144182
    I have a couple of methods declared at the namespace level within a header for a class: // MyClass.h namespace network { int Method1(double d); int Method2(double d); class MyClass { //... } } then defined in //MyClass.cpp int Method1(double d) { ... } int Method2(double d) { ... } This project compiles cleanly and is a dependency for a ui project which uses MyClass. The functions were previously member functions of MyClass, but were moved to namespace since it was more appropriate. My problem is the ui project complains when it gets to the linker: 1network.lib(MyClass.obj) : error LNK2001: unresolved external symbol "int __cdecl network::Method1(double)" (?INT@ds@sim@@YAHN@Z) 1network.lib(MyClass.obj) : error LNK2001: unresolved external symbol "int __cdecl network::Method2(double)" (?CINT@ds@sim@@YAHN@Z) What am I doing wrong?

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  • C++: Where can I define the body for a private function?

    - by Martijn Courteaux
    Hi, I have a header like this (header guards not shown): class GameSystem { public: GameSystem(Game *pcGame); virtual ~GameSystem(); void Setup(); private: void InitGame(); void RunGame(); void ExitGame(); Game *m_pcGame; /* Properties */ int m_nWidth; int m_nHeight; int m_nFps; bool m_bFullscreen; }; Where can I define the body for InitGame(), RunGame() and ExitGame()? Can I define it in my .cpp file? If so, how? Or am I obliged to make their body in my .h file? I'm using Eclipse and I began typing: void GameSystem:: and then he doesn't suggest the private functions.

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  • XCode 5 says I got a duplicate, which I don't

    - by GoodMove
    The point is every time I try to run a C++ code in XCode 5 (the file s "File.cpp") xcode returns this: duplicate symbol _main ld: 1 duplicate symbol for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation) And it only returns the error, when I got the following function whatever it contains: int main() { } I checked the folder, which XCode points to (where it says the duplicates are placed), but didn't find anything though. What am I supposed to do??? #include "File.h" using namespace std; void func (void){ cout << "Hello World!" << endl; }

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  • Dynamic-linked DLL needs to share a global variable with its caller.

    - by Fabian Wickborn
    I have a static library libStatic that defines a global variable like this Header file libStatic/globals.h: extern int globvar; Code file libStatic/globals.cpp: int globvar = 42; The DLL libDynamic and the executable runner are using this global variable. Furtheron, libDynamic is linked at run-time into runner (via LoadLibrary(), GetProcAddress(), and the works...) I understand this will lead to globvar being created twice, once in the heap of runner and once in the heap of libDynamic, which is of course very undesirable. Is there a good away around this? How can I ensure that libDynamic and runner are using the same globvar?

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  • c++ Sorting a vector based on values of other vector, or what's faster?

    - by pollux
    Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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