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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Where do you hang your semantic information, html?

  - by bobobobo

  Well, I keep putting semantic information about what an element means for the page logically in the class attribute <li class="phone-number">555-5555</li> It seems to work for this dual purpose of hanging semantic information and a pointer to how to style it. I'm not sure if this is the best idea, I'm trying to see if others have other ways of doing it. I also started to use a hidden input: <li>555-5555 <input class="semantics" type="hidden" value="phone-number" /></li> inside an element, so with jQuery, I can retrieve additional information about the element using li.find( '.semantics' ).val() To get an element's semantics from JavaScript

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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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• CSS Position Help (horizontal sidebar showing up when animate content over)

  - by jstacks

  Let me try my best to explain what I'd like to have happen, show you the code I have an hopefully I can get some help. So, I'm trying to do a sliding navigation UI from the left side of the screen (like a lot of mobile apps). The main content slides over, displaying the navigation menu beneath. Right now the browser thinks the screen is getting wider and introduces a horizontal scroll bar. However, I don't want that to happen... How do I get the div to animate off screen but not enlarge the width of the screen (i.e. keep it partially off screen)? Anyway here is my fiddle: http://jsfiddle.net/2vP67/6/ And here is the code within the post: HTML <div id='wrapper'> <div id='navWide'> </div> <div id='containerWide'> </div> <div id='containerTall'> <div id='container'> <div id='nav'> <div id='navNavigate'> Open Menu </div> <div id='navNavigateHide'> Close Menu </div> </div> </div> </div> <div id='sideContainerTall'> <div id='sideContainer'> <div id='sideNav'>Side Navigation </div> </div> </div> </div> CSS #wrapper { width:100%; min-width:1000px; height:100%; min-height:100%; position:relative; top:0; left:0; z-index:0; } #navWide { color: #ffffff; background:#222222; width:100%; min-width:1000px; height:45px; position:fixed; top:0; left:0; z-index:100; } #containerWide { width:100%; min-width:1000px; min-height:100%; position:absolute; top:45px; z-index:100; } #containerTall { color: #000000; background:#dadada; width:960px; min-height:100%; margin-left:-480px; position:absolute; top:0; left:50%; z-index:1000; } /***** main container *****/ #container { width:960px; min-height:585px; } #nav { color: #ffffff; background:#222222; width:960px; height:45px; position:fixed; top:0; z-index:10000; } #navNavigate { background:yellow; font-size:10px; color:#888888; width:32px; height:32px; padding:7px 6px 6px 6px; float:left; cursor:pointer; } #navNavigateHide { background:yellow; font-size:10px; color:#888888; width:32px; height:32px; padding:7px 6px 6px 6px; float:left; cursor:pointer; display:none; } #sideContainerTall { background:#888888; width:264px; min-height:100%; margin-left:-480px; position:absolute; top:0; left:50%; z-index:500; } #sideContainer { width:264px; min-height:585px; display:none; } #sideContainerTall { background:#888888; width:264px; min-height:100%; margin-left:-480px; position:absolute; top:0; left:50%; z-index:500; } #sideContainer { width:264px; min-height:585px; display:none; } #sideNav { width:264px; height:648px; float:left; } Javascript $(document).ready(function() { $('div#navNavigate').click(function() { $('div#navNavigate').hide(); $('div#navNavigateHide').show(); $('div#sideContainer').show(); $('div#containerTall').animate({ 'left': '+=264px' }); }); $('div#navNavigateHide').click(function() { $('div#navNavigate').show(); $('div#navNavigateHide').hide(); $('div#containerTall').animate({ 'left': '-=264px' }, function() { $('div#sideContainer').hide(); }); }); });

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• How to Change Type of a VARIANT

  - by nimo

  Hi, I'm having a VARIANT with its type set to VT_R8. Subsequently I need to change its type to VT_BSTR. I would like know whether there is a way of resetting a VARIANT status. Thus, I noticed that every time I set value to the VARIANT (in my case, its double) , VARIANT itself set its bstrVal member to a bad pointer, even though I set bstrVal member to NULL at the initialization of VARIANT. Why such thing is happening ? Is it safe to use a VARIANT as structure where both dbVal and bstrVal member are set ? Please clarify, thank you.

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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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• Boost ASIO read X bytes synchroniously into a vector

  - by xeross

  Hey, I've been attempting to write a client/server app with boost now, so far it sends and receives but I can't seem to just read X bytes into a vector. If I use the following code vector<uint8_t> buf; for (;;) { buf.resize(4); boost::system::error_code error; size_t len = socket.read_some(boost::asio::buffer(buf), error); if (error == boost::asio::error::eof) break; // Connection closed cleanly by peer. else if (error) throw boost::system::system_error(error); // Some other error. } And the packet is bigger then 4 bytes then it seems it keeps writing into those 4 bytes until the entire packet has been received, however I want it to fetch 4 bytes, then allow me to parse them, and then get the rest of the packet. Can anyone provide me with a working example, or at least a pointer on how to make it work properly ? Regards, Xeross

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• c++: truth assignment warning with arguments?

  - by John

  I use the following to work with arguments in my programs, but it seems to just hand me a warning (just a warning): "warning: suggest parentheses around assignment used as truth value" The beginning of the code is as follows: enum{OPT_DISP_H = 0x2, OPT_DISP_W = 0x1}; int main(int argc, char *argv[]) { int opt = 0x00; char c; while((++argv)[0] && argv[0][0]=='-'){ while(c =* ++argv[0]) switch(c){ case 'h': opt |= OPT_DISP_H; break; //etc.. The while(c =* ++argv[0]) part being where the warning persists. The code works fine, but what does this warning mean opposed to what is used? I think the code is c = *++argv[0], using the pointer. So why does the single = work and what is really recommended to be used?

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