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  • C++ inheritance question

    - by user233973
    Hi guys, I have a C++ inheritance related question. I have a set of classes like this (I have not given the complete class structure coz I am lazy :) ). I want to access chiComponent class public methods using com pointer. How should I go about it? Note that I am having to change the object which "com" is pointing to in a lot of places. So I do not think I can have another chiComponent *ccom = <some_cast> com; ccom.chiComponentMethod() How should I go about it? class Component{ }; class chiComponent : public Component { public: void chiComponentMethod() { cout << "Hi! Chi component function called!!"; } } class parent { protected: Component *com; }; class child : public parent{ public: child() { com = new chiComponent(); } } Regards Arun

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  • What is the logic behind defining macros inside a struct?

    - by systemsfault
    As apparent in the title, I'm questioning the reason behind defining the macros inside a struct. I frequently see this approach in network programming for instance following snippet: struct sniff_tcp { u_short th_sport; /* source port */ u_short th_dport; /* destination port */ tcp_seq th_seq; /* sequence number */ tcp_seq th_ack; /* acknowledgement number */ u_char th_offx2; /* data offset, rsvd */ #define TH_OFF(th) (((th)->th_offx2 & 0xf0) >> 4) u_char th_flags; #define TH_FIN 0x01 #define TH_SYN 0x02 #define TH_RST 0x04 #define TH_PUSH 0x08 #define TH_ACK 0x10 #define TH_URG 0x20 #define TH_ECE 0x40 #define TH_CWR 0x80 #define TH_FLAGS (TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG|TH_ECE|TH_CWR) u_short th_win; /* window */ u_short th_sum; /* checksum */ u_short th_urp; /* urgent pointer */ }; This example is from sniffex.c code in tcpdump's web site. Is this for enhancing readability and making code clearer.

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  • How do I change the class of an object to a subclass of its current class in C++?

    - by Jared P
    I have an array of pointers to a base class, so that I can make those pointers point to (different) subclasses of the base class, but still interact with them. (really only a couple of methods which I made virtual and overloaded) I'm wondering if I can avoid using the pointers, and instead just make an array of the base class, but have some way to set the class to the subclass of my choosing. I know there must be something there specifying the class, as it needs to use that to look up the function pointer for virtual methods. By the way, the subclasses all have the same ivars and layout. Note: the design is actually based on using a template argument instead of a variable, due to performance increases, so really the abstract base class is just the interface for the subclasses, which are all the same except for their compiled code. Thanks

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  • Reading a file over a network path

    - by Sin5k4
    I have this weird issue,when I use > File FileToRead = new File("\\\\MYSERVER\\MYFOLDER\\MYFOLDER\\MYPICTURE.JPG"); to read a file over a network,all I get is a null pointer exception.Normally a local path works with this,but when on a network path,I just couldn't manage to get it to work.Any ideas? PS:oh and my network connection seems to work,no issues when accessing data in windows explorer... More of the code: File FileToRead = new File("file://DOKSERVICE/Somefolder/ProductImage/01001.JPG"); // File FileToRead = new File("c:\\dog.jpg"); local test BufferedImage image = ImageIO.read(FileToRead); BufferedImage resizedimage = new BufferedImage(260, 260,BufferedImage.TYPE_INT_RGB ); Graphics2D g = resizedimage.createGraphics(); g.drawImage(image, 0, 0, 260, 260, null); g.dispose(); picture.setIcon(new ImageIcon(image));

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  • Looking at the C++ new[] cookie. How portable is this code?

    - by carleeto
    I came up with this as a quick solution to a debugging problem - I have the pointer variable and its type, I know it points to an array of objects allocated on the heap, but I don't know how many. So I wrote this function to look at the cookie that stores the number of bytes when memory is allocated on the heap. template< typename T > int num_allocated_items( T *p ) { return *((int*)p-4)/sizeof(T); } //test #include <iostream> int main( int argc, char *argv[] ) { using std::cout; using std::endl; typedef long double testtype; testtype *p = new testtype[ 45 ]; //prints 45 std::cout<<"num allocated = "<<num_allocated_items<testtype>(p)<<std::endl; delete[] p; return 0; } I'd like to know just how portable this code is.

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  • What exactly does a self-describing type in .Net mean?

    - by tzup
    Given this MSDN article, we learn that the Common Type System in .Net has this classification of reference types: "Reference types can be self-describing types, pointer types, or interface types. The type of a reference type can be determined from values of self-describing types. Self-describing types are further split into arrays and class types." So an array, for instance, is a self-describing type because we can determine it's type from its values? How? Is that it, or is there more to this definition?

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  • const ready only local copies

    - by robUK
    Hello gcc 4.4.4 c89 I am just wondering is it worth passing a const into a function. i.e. void do_something(const char *dest, const int size) The size is a ready-only so I don't want to change it. However, some developers never have this as const has it is a local copy that is being used. The pointer is const as you can change the value in the calling routine. I always have a const on ready-only local copies, as it confirms to anyone reading my code that it is a ready-only variable. And also, when coding I don't make the mistake of changing it without realizing. Many thanks for any suggestions,

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  • std::out_of_range error?

    - by vette982
    I'm dealing with a file with a linked list of lines with each node looking like this: struct TextLine{ //The actual text string text; //The line number of the document int line_num; //A pointer to the next line TextLine * next; }; and I'm writing a function that adds spaces at the beginning of the lines found in the variable text, by calling functions like linelist_ptr->text.insert(0,1,'\t'); The program compiles, but when I run it I get this error: terminate called after throwing an instance of 'std::out_of_range' what(): basic_string::at Aborted Any ideas?

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  • How to return a copy of the data in C++

    - by Josh Curren
    I am trying to return a new copy of the data in a C++ Template class. The following code is getting this error: invalid conversion from ‘int*’ to ‘int’. If I remove the new T then I am not returning a copy of the data but a pointer to it. template<class T> T OrderedList<T>::get( int k ) { Node<T>* n = list; for( int i = 0; i < k; i++ ) { n=n->get_link(); } return new T( n->get_data() ); // This line is getting the error ********** }

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  • Passing arguments to Shared Function - C

    - by SpyrosR
    I have used dlopen to load an object and dlsym to get a function pointer to a shared object function. Everything works fine. I have tested it calling then the shared function which (for now) only prints and it works-prints fine in the main program calling it. Now I want to pass two arguments to this function. An int and a char * .Can anyone help me understand how can I pass arguments to a shared function? I have searched in the web but I cannot understand how it works.

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  • Official definition of CSCI (Computer Software Configuration Item)

    - by Andreas_D
    I'm looking for the most official definition of CSCI / Configuration Item - not just what it is but what we have to deliver / can expect when a contract defines subsystems which shall be developed as configuration items. I spend some time with my famous search tool and found a lot of explanations for CSCI (wikipedia, acronym directories, ...) but I haven't found a standard or a pointer to a standard (like ISO-xxx) yet which tells (1) what it is and (2) what has to be done from a QM/CM point of view. I just ask, because a contractors QM representative stated during an acceptance test, that CI only requires to not forget the CI in the configuration plan and to assign a serial number ... I expected to see some SRS, SDD, ICD, SVD, SIP, ... documents and acceptance test documentation for those subsystems...

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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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  • Expected symbol problems with this function declaration

    - by Derek
    I am just getting back into the C programming realm and I am having an issue that I think is linker related. I am using cmake for the first time as well, so that could be adding to my frustration. I have included a third party header file that contains a typedef that my code is trying to use, and it has this line: typedef struct a a_t so my code has a_t *var; //later..... var->member;// this line throws the error which throws the error: dereferencing pointer to incomplete type So am I just missing another include file, or is this a linker issue? I am building this code in QtCreator and using cmake. I can dive on a_t to see that typedef declaration in the included header, but I can't seem to dive on "struct a" itself to see where it's coming from. Thanks

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  • I serialized a C++ object, how to allocate memory for it without knowing what type it is?

    - by Neo_b
    Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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  • How to create a Mutex with security attribute to share resource from different application?

    - by Antony Tess
    How to create a Mutex with security attribute rigth to share resource from different application? In according with Microsoft SDK documentation the CreateMutex API accept as first parameter a SECURITY_ATTRIBUTES pointer. HANDLE WINAPI CreateMutex( __in LPSECURITY_ATTRIBUTES lpMutexAttributes, __in BOOL bInitialOwner, __in LPCTSTR lpName ); I want to create the rigth security attribute so only my application group can open the MUTEX and access to a specific resource (a file) where my application gruop read/write data operation. The target opertaing system are XP, Vista and Seven. The feature must working in both, administrator/standard user, login shenario.

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  • How to get "printer ready bytes" from a source in c#?

    - by luis_villase
    Hey everyone! I'm in a bit of trouble here, hoping you can help a fellow programmer out. I have an application that receives a pointer to raw bytes (plus length and stuff) and sends said raw data to a printer. This is important, I have no choice but to use this method to get any printing done. If I send a raw string, it will print with no problem. However, I need to be able to print formatted text, images, etc. So the thing is... I would like to be able to get printer ready bytes from a given source (maybe a pdf, or html, does not matter as long as it contains formatted text and/or images). It would be like "splitting" the print command like so: a) Open file and read data b) Load printer data into memory c) Send bytes to printer Obviously, I've got a) and c) covered, it's b) the one that's breaking my head. Any thoughts? Thanks in advance for your help.

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  • Rails 3 namespacing requires model to be defined twice?

    - by RSG
    I'm pulling my hair out trying to understand namespacing in Rails 3. I've tried following a few different tutorials, and the only way I can get my models to work is if I define my model in both the base directory and my namespace directory. If I only define the model in the namespace directory it expects it to define both Model and Namespace::Model, as below: LoadError (Expected .../app/models/plugins/chat.rb to define Chat): or LoadError (Expected .../app/models/plugins/chat.rb to define Plugins::Chat): I'm sure I'm missing something obvious, but I could really use a pointer in the right direction. Here are the relevant excerpts. /models/plugins/chat.rb class Plugins::Chat include ActiveModel::Validations include ActiveModel::Conversion extend ActiveModel::Naming ... end /controllers/plugins/chats_controller.rb class Plugins::ChatsController < Plugins::ApplicationController load_and_authorize_resource ... end /config/routes.rb namespace :plugins do resources :chats end /config/application.rb config.autoload_paths += Dir["#{config.root}/app/models/**/"]

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  • How to get notified of modification in the memory in Linux

    - by Song Yuan
    In a userspace program in Linux, I get a piece of memory via allocation from the heap, then the pointer is distributed to a lot of other components running in other threads to use. I would like to get notified when the said piece of memory is modified. I can of course develop a custom userspace solution for other components to use when they try to modify the memory. The problem in my case is that these are legacy components and they can write to memory in many occasions. So I'm wondering whether there is a similar API like inotify (get notified when file is changed) or other approaches in order to get notified when a piece of memory is changed. I considered using mmap and inotify, which obviously won't work if the changes are not flushed. Any suggestions are appreciated :-)

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  • collect string in loop and printout all the string outside loop

    - by user1508163
    I'm newbie here and there is some question that I want have some lesson from you guys. For example: #include <stdio.h> #include<stdlib.h> #include<ctype.h> void main() { char name[51],selection; do { printf("Enter name: "); fflush(stdin); gets(name); printf("Enter another name?(Y/N)"); scanf("%c",&selection); selection=toupper(selection); }while (selection=='Y'); //I want to printout the entered name here but dunno the coding printf("END\n"); system("pause"); } As I know when the loops perform will overwrite the variable then how I perform a coding that will printout all the name user entered? I have already ask my tutor and he is ask me to use pointer, can anyone guide me in this case?

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  • GWT : NULL Session

    - by jidma
    I'm using spring4gwt in my project. I have the following login service implementation: @Service("loginService") public class LoginServiceImpl extends RemoteServiceServlet implements LoginService { @Override @Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class) public UserBean checkUser(String userName, String password) throws Exception { HttpSession httpSession = getThreadLocalRequest().getSession(); } } When i call the loginService.checkUser("test","test") (In hosted mode), I get a null pointer exception, as getThreadLocalRequest() returns NULL instead of the actual session. I didn't try in web mode yet. Why would I get a null session ? Does it have something to do with spring4gwt ? Thank you

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  • MySQL: host name universal change.

    - by ctrlShiftBryan
    I am making some updates to a php site which I did not design. I have a local copy of the site. At the top of each page there are settings for the host name for the db connection. Is there someway I can setup a pointer to the remote address. The address is 'mysqlhost' for example and I want that to point to 'mysql.myhost.com'. I tried creating a HOST record for mysqlhost pointing to the IP address it resolves to but that doesn't work. If I put 'mysql.myhost.com' in the connection it works. If I put that IP address it doesn't so that is probably why the HOST record idea doesn't work. Other than creating a local copy of the DB is there a quick way so that I don't have to modify each file in my dev environment and then again when I redeploy?

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  • Event handling C# / Registering a callback

    - by Jeff Dahmer
    Events can only return void and recieve object sender/eventargs right? If so then craptastic.... how can I pass a function pointer to another obj, like: public bool ACallBackFunc(int n) { return n > 0; } public void RegisterCallback(Something s) { s.GiveCallBack(this.ACallBackFunc); } Something::GiveCallBack(Action? funcPtr) I tried using Action, but I need it to return some value and Actions can only return void. Also, we do not know what kind of a callback we will be recieving; it could return anything and have any params! Reflection will have to be used somehow I reckon.

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  • Swap byte 2 and 4 from integer

    - by czar x
    I had this interview question - Swap byte 2 and byte4 within an integer sequence. Integer is a 4byte wide i.e. 32 bits My approach was to use char *pointer and a temp char to swap the bytes. For clarity i have broken the steps otherwise an character array can be considered. unsigned char *b2, *b4, tmpc; int n = 0xABCD; b2 = &n; b2++; b4 = &n; b4 +=3; ///swap the values; tmpc = *b2; *b2 = *b4; *b4 = tmpc; Any other methods?

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  • HRESULT exception not caught in VS 2008

    - by arionik
    Hello all, I've got a stange situation in visual studio 2008 C++. I work on code that was originally written for visual studio 2003, where everything works well. Now, ported to VS 2008, the exception handling, which unfortuantely exists widely in the code, does not work anymore. standard code example: try { HRESULT hr = S_OK; // do stuff... if( FAILED( hr ) ) throw hr; } catch( HRESULT hr ) { // error handling, but we never get here } catch( ... ) { // ... not even here } Under VS 2008, no exception is encountered, but I get a crash somewhere else, indicating that the stack pointer must be screwed up. Did anybody come across this behaviour? Any help is appreciated.

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  • HTML5 placing image where i want it on screen

    - by corrigan_sam
    I have a little start screen running and i want the image, which is acting as a button, to placed at a certain point, but when i try to it stays in the same place, and i don't know how i can get it to stay in the place i want it. Here is my code, its is HTML with some css: <style> #SplashScreen{ position:relative; overflow:hidden; } #StartButton { cursor:pointer; position:absoloute; left:100px; top:100px; } </style> <div id="SplashScreen" width="400" height="400"> <h1>Game Title</h1> <img id="StartButton" src="play.png"/> </div> The image just draws underneath the title and not where i want it. Any help?

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