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• Modal QMessageBox does not behave like native Windows dialogs

  - by Philip Daubmeier

  My application has a dialog that asks the user via a QMessageBox whether he wants to discard all changes he made or wants to keep editing. I want this dialog to be modal to the whole application. I read somewhere that this is the standard behavior for a QMessageBox, so I dont have to set it explicitly with something like: mbox.setWindowModality(Qt::ApplicationModal); I wonder why it behaves differently from other modal dialogs in the OS (Windows 7 in my case). On the one hand it functions like it should, i.e. all other input methods in the application are blocked until the user answeres the dialog. However, it doesn't 'blink'* if the user clicks any other window of the application. Is there any way to get Qt to behave like a native Windows dialog? Thanks in advance! *If you don't know what I mean with this 'blinking': Just open notepad on a Windows OS, type some text and try to close it. A dialog pops up that asks to save, discard or keep editing. Now click somewhere on the editor window - the border and titlebar of the dialog flashes/blinks a few times.

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• friend declaration in C++

  - by Happy Mittal

  In Thinking in C++ by Bruce eckel, there is an example given regarding friend functions as // Declaration (incomplete type specification): struct X; struct Y { void f(X*); }; struct X { // Definition private: int i; public: friend void Y::f(X*); // Struct member friend }; void Y::f(X* x) { x->i = 47; } Now he explained this: Notice that Y::f(X*) takes the address of an X object. This is critical because the compiler always knows how to pass an address, which is of a fixed size regardless of the object being passed, even if it doesn’t have full information about the size of the type. If you try to pass the whole object, however, the compiler must see the entire structure definition of X, to know the size and how to pass it, before it allows you to declare a function such as Y::g(X). But when I tried void f(X); as declaration in struct Y, it shows no error. Please explain why?

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• iPhone OpenGLES: Textures are consuming too much memory and the program crashes with signal "0"

  - by CustomAppsMan

  I am not sure what the problem is. My app is running fine on the simulator but when I try to run it on the iPhone it crashes during debugging or without debugging with signal "0". I am using the Texture2D.m and OpenGLES2DView.m from the examples provided by Apple. I profiled the app on the iPhone with Instruments using the Memory tracer from the Library and when the app died the final memory consumed was about 60Mb real and 90+Mb virtual. Is there some other problem or is the iPhone just killing the application because it has consumed too much memory? If you need any information please state it and I will try to provide it. I am creating thousands of textures at load time which is why the memory consumption is so high. Really cant do anything about reducing the number of pics being loaded. I was running before on just UIImage but it was giving me really low frame rates. I read on this site that I should use OpenGLES for higher frame rates. Also sub question is there any way not to use UIImage to load the png file and then use the Texture class provided to create the texture for OpenGLES functions to use it for drawing? Is there some function in OpenGLES which will create a texture straight from a png file?

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• Show div based on getDay and getHours + getMinutes

  - by Peta Reardon

  I am building a website for a radio station and want to show which presenter is currently on air. I have built a web app that contains data on the presenter: name, photo, bio and start/end times for each weekday. <div id="presenter1"> <div class="slot"> <div id="sunday-off"> - </div> <div id="monday-afternoon">12:00 - 15:59</div> <div id="tuesday-afternoon">12:00 - 15:59</div> <div id="wednesday-afternoon">12:00 - 15:59</div> <div id="thursday-afternoon">12:00 - 15:59</div> <div id="friday-afternoon">12:00 - 15:59</div> <div id="saturday-morning">06:00 - 08:59</div> </div> </div> What I would like to do is use Javascript functions getDay() and getHours() + getMinutes() to show only the presenter that is scheduled to be on air based on the times specified in the app. The main part I am having difficulty with is with determining whether this presenter falls within the current time and then showing/hiding the div as necessary. Any help or guidance on how I can acheive this would be greatly appreciated.

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• Thread mutex behaviour

  - by Alberteddu

  Hi there, I'm learning C. I'm writing an application with multiple threads; I know that when a variable is shared between two or more threads, it is better to lock/unlock using a mutex to avoid deadlock and inconsistency of variables. This is very clear when I want to change or view one variable. int i = 0; /** Global */ static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /** Thread 1. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); /** Thread 2. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); This is correct, I think. The variable i, at the end of the executions, contains the integer 2. Anyway, there are some situations in which I don't know exactly where to put the two function calls. For example, suppose you have a function obtain(), which returns a global variable. I need to call that function from within the two threads. I have also two other threads that call the function set(), defined with a few arguments; this function will set the same global variable. The two functions are necessary when you need to do something before getting/setting the var. /** (0) */ /** Thread 1, or 2, or 3... */ if(obtain() == something) { if(obtain() == somethingElse) { // Do this, sometimes obtain() and sometimes set(random number) (1) } else { // Do that, just obtain(). (2) } } else { // Do this and do that (3) // If # of thread * 3 > 10, then set(3*10) For example. (4) } /** (5) */ Where I have to lock, and where I have to unlock? The situation can be, I think, even more complex. I will appreciate an exhaustive answer. Thank you in advance. —Alberto

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• Passing functor and function pointers interchangeably using a templated method in C++

  - by metroxylon

  I currently have a templated class, with a templated method. Works great with functors, but having trouble compiling for functions. Foo.h template <typename T> class Foo { public: // Constructor, destructor, etc... template <typename Func> void bar(T x, Func f); }; template <typename T> template <typename Func> Foo::bar(T x, Func f) { /* some code here */ } Main.cpp #include "Foo.h" template <typename T> class Functor { public: Functor() {} void operator()(T x) { /* ... */ } private: /* some attributes here */ }; void Function(T x) { /* ... */ } int main() { Foo<int> foo; foo.bar(2, Functor); // No problem foo.bar(2, Function); // <unresolved overloaded function type> return 0; }

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• Friends, templates, overloading <<

  - by Crystal

  I'm trying to use friend functions to overload << and templates to get familiar with templates. I do not know what these compile errors are: Point.cpp:11: error: shadows template parm 'class T' Point.cpp:12: error: declaration of 'const Point<T>& T' for this file #include "Point.h" template <class T> Point<T>::Point() : xCoordinate(0), yCoordinate(0) {} template <class T> Point<T>::Point(T xCoordinate, T yCoordinate) : xCoordinate(xCoordinate), yCoordinate(yCoordinate) {} template <class T> std::ostream &operator<<(std::ostream &out, const Point<T> &T) { std::cout << "(" << T.xCoordinate << ", " << T.yCoordinate << ")"; return out; } My header looks like: #ifndef POINT_H #define POINT_H #include <iostream> template <class T> class Point { public: Point(); Point(T xCoordinate, T yCoordinate); friend std::ostream &operator<<(std::ostream &out, const Point<T> &T); private: T xCoordinate; T yCoordinate; }; #endif My header also gives the warning: Point.h:12: warning: friend declaration 'std::ostream& operator<<(std::ostream&, const Point<T>&)' declares a non-template function Which I was also unsure why. Any thoughts? Thanks.

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• PHP / Zend custom date input formats

  - by mld

  Hi, I'm creating a library component for other developers on my team using PHP and Zend. This component needs to be able to take as input a date (string) and another string telling it the format of that date. Looking through the Zend documentation and examples, I thought I found the solution - $dateObject = Zend_Date('13.04.2006', array('date_format' => 'dd.MM.yyyy')); this line, however, throws an error - call to undefined function. So instead I tried this - $dt = Zend_Locale_Format::getDate('13.04.2006', array('date_format' => 'dd.MM.yyyy')); This gets the job done, but throws an error if a date that is entered isn't valid. The docs make it look like you can use the isDate() function to check validity - Zend_Date::isDate('13.04.2006', array('date_format' => 'dd.MM.yyyy')) but this line always returns false. So my questions - Am I going about this the right way? If not, is there a better way to handle this via Zend or straight PHP? If I do use Zend_Locale_Format::getDate(), do I need to worry about a locale being set elsewhere and changing the results of the call? I'm locked into PHP 5.2.6 on windows, btw... so 5.3+ functions & strptime() are out.

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• C++ - Basic WinAPI question

  - by HardCoder1986

  Hello! I am now working on a some sort of a game engine and I had an idea to put everything engine-related into a static library and then link it to my actual problem. Right now I achieved it and actually link that library and every functions seem to work fine, except those, which are windows-related. I have a chunk of code in my library that looks like this: hWnd = CreateWindow(className, "Name", WS_OVERLAPPED | WS_CAPTION | WS_EX_TOPMOST, 0, 0, 800, 600, NULL, NULL, GetModuleHandle(NULL), this); if (hWnd) { ShowWindow(hWnd, SW_NORMAL); UpdateWindow(hWnd); } else { MessageBox(NULL, "Internal program error", "Error", MB_OK | MB_ICONERROR); return; } When this code was not in the library, but in the actual project, it worked fine, created the window and everything was ok. Right now (when I'm linking to my library that contains this code) CreateWindow(...) call returns NULL and GetLastError() returns "Operation succesfully completed" (wtf?). Could anybody help me with this? Is it possible to create a window and display it using a static library call and why could my code fail? Thank you.

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• Proper Memory Management for Objective-C Method

  - by Justin

  Hi, I'm programming an iPhone app and I had a question about memory management in one of my methods. I'm still a little new to managing memory manually, so I'm sorry if this question seems elementary. Below is a method designed to allow a number pad to place buttons in a label based on their tag, this way I don't need to make a method for each button. The method works fine, I'm just wondering if I'm responsible for releasing any of the variables I make in the function. The application crashes if I try to release any of the variables, so I'm a little confused about my responsibility regarding memory. Here's the method: FYI the variable firstValue is my label, it's the only variable not declared in the method. -(IBAction)inputNumbersFromButtons:(id)sender { UIButton *placeHolderButton = [[UIButton alloc] init]; placeHolderButton = sender; NSString *placeHolderString = [[NSString alloc] init]; placeHolderString = [placeHolderString stringByAppendingString:firstValue.text]; NSString *addThisNumber = [[NSString alloc] init]; int i = placeHolderButton.tag; addThisNumber = [NSString stringWithFormat:@"%i", i]; NSString *newLabelText = [[NSString alloc] init]; newLabelText = [placeHolderString stringByAppendingString:addThisNumber]; [firstValue setText:newLabelText]; //[placeHolderButton release]; //[placeHolderString release]; //[addThisNumber release]; //[newLabelText release]; } The application works fine with those last four lines commented out, but it seems to me like I should be releasing these variables here. If I'm wrong about that I'd welcome a quick explanation about when it's necessary to release variables declared in functions and when it's not. Thanks.

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• How do I "rebind" the click event after unbind('click') ?

  - by Ben

  I have an anchor tag <a class="next">next</a> made into a "button". Sometimes, this tag needs to be hidden if there is nothing new to show. All works fine if I simply hide the button with .hide() and re-display it with .show(). But I wanted to uses .fadeIn() and .fadeOut() instead. The problem I'm having is that if the user clicks on the button during the fadeOut animation, it can cause problems with the logic I have running the show. The solution I found was to unbind the click event from the button after the original click function begins, and then re-bind it after the animation is complete. $('a.next').click(function() { $(this).unbind('click'); ... // calls some functions, one of which fades out the a.next if needed ... $(this).bind('click'); } the last part of the above example does not work. The click event is not actually re-bound to the anchor. does anyone know the correct way to accomplish this? I'm a self-taught jquery guy, so some of the higher level things like unbind() and bind() are over my head, and the jquery documentation isn't really simple enough for me to understand.

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• PHP: Extract direct sub directory from path string

  - by Nebs

  I need to extract the name of the direct sub directory from a full path string. For example, say we have: $str = "dir1/dir2/dir3/dir4/filename.ext"; $dir = "dir1/dir2"; Then the name of the sub-directory in the $str path relative to $dir would be "dir3". Note that $dir never has '/' at the ends. So the function should be: $subdir = getsubdir($str,$dir); echo $subdir; // Outputs "dir3" If $dir="dir1" then the output would be "dir2". If $dir="dir1/dir2/dir3/dir4" then the output would be "" (empty). If $dir="" then the output would be "dir1". Etc.. Currently this is what I have, and it works (as far as I've tested it). I'm just wondering if there's a simpler way since I find I'm using a lot of string functions. Maybe there's some magic regexp to do this in one line? (I'm not too good with regexp unfortunately). function getsubdir($str,$dir) { // Remove the filename $str = dirname($str); // Remove the $dir if(!empty($dir)){ $str = str_replace($dir,"",$str); } // Remove the leading '/' if there is one $si = stripos($str,"/"); if($si == 0){ $str = substr($str,1); } // Remove everything after the subdir (if there is anything) $lastpart = strchr($str,"/"); $str = str_replace($lastpart,"",$str); return $str; } As you can see, it's a little hacky in order to handle some odd cases (no '/' in input, empty input, etc). I hope all that made sense. Any help/suggestions are welcome.

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• How to write a "thread safe" function in C ?

  - by Andrei Ciobanu

  Hello I am writing some data structures in C, and I've realized that their associated functions aren't thread safe. The i am writing code uses only standard C, and I want to achieve some sort of 'synchronization'. I was thinking to do something like this: enum sync_e { TRUE, FALSE }; typedef enum sync_e sync; struct list_s { //Other stuff struct list_node_s *head; struct list_node_s *tail; enum sync_e locked; }; typedef struct list_s list; , to include a "boolean" field in the list structure that indicates the structures state: locked, unlocked. For example an insertion function will be rewritten this way: int list_insert_next(list* l, list_node *e, int x){ while(l->locked == TRUE){ /* Wait */ } l->locked = TRUE; /* Insert element */ /* -------------- */ l->locked = FALSE; return (0); } While operating on the list the 'locked' field will be set to TRUE, not allowing any other alterations. After operation completes the 'locked' field will be again set to 'TRUE'. Is this approach good ? Do you know other approaches (using only standard C).

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• System Calls in windows & Native API?

  - by claws

  Recently I've been using lot of Assembly language in *NIX operating systems. I was wondering about the windows domain. Calling convention in linux: mov $SYS_Call_NUM, %eax mov $param1 , %ebx mov $param2 , %ecx int $0x80 Thats it. That is how we should make a system call in linux. Reference of all system calls in linux: Regarding which $SYS_Call_NUM & which parameters we can use this reference : http://docs.cs.up.ac.za/programming/asm/derick_tut/syscalls.html OFFICIAL Reference : http://kernel.org/doc/man-pages/online/dir_section_2.html Calling convention in Windows: ??? Reference of all system calls in Windows: ??? Unofficial : http://www.metasploit.com/users/opcode/syscalls.html , but how do I use these in assembly unless I know the calling convention. OFFICIAL : ??? If you say, they didn't documented it. Then how is one going to write libc for windows without knowing system calls? How is one gonna do Windows Assembly programming? Atleast in the driver programming one needs to know these. right? Now, whats up with the so called Native API? Is Native API & System calls for windows both are different terms referring to same thing? In order to confirm I compared these from two UNOFFICIAL Sources System Calls: http://www.metasploit.com/users/opcode/syscalls.html Native API: http://undocumented.ntinternals.net/aindex.html My observations: All system calls are beginning with letters Nt where as Native API is consisting of lot of functions which are not beginning with letters Nt. System Call of windows are subset of Native API. System calls are just part of Native API. Can any one confirm this and explain.

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• In Emacs, how can I use imenu more sensibly with C#?

  - by Cheeso

  I've used emacs for a long time, but I haven't been keeping up with a bunch of features. One of these is speedbar, which I just briefly investigated now. Another is imenu. Both of these were mentioned in in-emacs-how-can-i-jump-between-functions-in-the-current-file? Using imenu, I can jump to particular methods in the module I'm working in. But there is a parse hierarchy that I have to negotiate before I get the option to choose (with autocomplete) the method name. It goes like this. I type M-x imenu and then I get to choose Using or Types. The Using choice allows me to jump to any of the using statements at the top level of the C# file (something like imports statements in a Java module, for those of you who don't know C#). Not super helpful. I choose Types. Then I have to choose a namespace and a class, even though there is just one of each in the source module. At that point I can choose between variables, types, and methods. If I choose methods I finally get the list of methods to choose from. The hierarchy I traverse looks like this; Using Types Namespace Class Types Variables Methods method names Only after I get to the 5th level do I get to select the thing I really want to jump to: a particular method. Imenu seems intelligent about the source module, but kind of hard to use. Am I doing it wrong?

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• making query from different related tables using codeigniter

  - by fatemeh karam

  I'm using codeigniter as i mentioned this is a part of my view code foreach($projects_query as $row)// $row indicates the projects { ?> <tr><td><h3><button type="submit" class="button red-gradient glossy" name = "project_click" > <?php echo $row->txtTaskName; ?></button></h3></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr> <?php foreach($tasks_query as $row2) { // if( $row->txtTaskName == "TestProject") if($row->intTaskID == $row2->intInside)// intInside indicades that the current task($row2) is the subset of which task (system , subsystem or project) { if($row2->intSummary == 0)//if the task(the system) is an executable task & doesn't have any subtask: { $query_team_user_id = $this->admin_in_out_model->get_user_team_task_query($row2->intTaskID);//runs the function and generates a query from tbl_userteamtask where intTaskID equals to the selected row's intTaskID foreach($query_team_user_id as $row_teamid) { $query_teamname = $this->admin_in_out_model->get_team_name($row_teamid->intTeamID); $query_fn_ln = $this->admin_in_out_model->get_fn_ln_from_userid($row_teamid->intUserID); foreach($query_teamname as $row_teamname) {?> <tr><td></td><td></td><td><h4> <?php echo $row2->txtTaskName;?></h4></td> <td><b><font color='#F33558'><?php echo $row_teamname->txtTeamName;?></font></b></td> <?php } foreach($query_fn_ln as $row_f_l_name) {?> <td> <?php echo $row_f_l_name->txtFirstname." ".$row_f_l_name->txtLastname;?></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td> <?php }?> </tr> <?php } } else{ ?> <tr><td></td><td></td><td><h4> <?php echo $row2->txtTaskName;?></h4></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><?php } foreach($tasks_query as $row_subsystems) { if($row_subsystems->intInside == $row2->intTaskID )//if the task is the subtask of a system(it means the task is a subsystem) { if($row_subsystems->intSummary == 0)//if the task is an executable task & doesn't have any subtask: { $query_team_user_id = $this->admin_in_out_model->get_user_team_task_query($row_subsystems->intTaskID); foreach($query_team_user_id as $row_teamid) {?> <tr><?php $query_teamname = $this->admin_in_out_model->get_team_name($row_teamid->intTeamID); $query_fn_ln = $this->admin_in_out_model->get_fn_ln_from_userid($row_teamid->intUserID); foreach($query_teamname as $row_teamname) {?> <td></td><td></td><td><h5><?php echo $row_subsystems->txtTaskName?></h5><br/></td> <td><b><font color='#F33558'><?php echo $row_teamname->txtTeamName;?></font></b></td><?php } foreach($query_fn_ln as $row_f_l_name) {?> <td><?php echo $row_f_l_name->txtFirstname." ".$row_f_l_name->txtLastname;?></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><?php }?> </tr><?php } } else{ ?><tr><td></td><td></td><td><h5><?php echo $row_subsystems->txtTaskName?></h5></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><?php } foreach($tasks_query as $row_tasks) { if($row_tasks->intInside == $row_subsystems->intTaskID )//if the task is the subtask of a subsystem { if($row_tasks->intSummary == 0)//if the task is an executable task & doesn't have any subtask: { $query_team_user_id = $this->admin_in_out_model->get_user_team_task_query($row_tasks->intTaskID); foreach($query_team_user_id as $row_teamid) {?> <tr><?php $query_teamname = $this->admin_in_out_model->get_team_name($row_teamid->intTeamID); $query_fn_ln = $this->admin_in_out_model->get_fn_ln_from_userid($row_teamid->intUserID); foreach($query_teamname as $row_teamname) {?> <td></td><td></td><td><b><?php echo $row_tasks->txtTaskName;?></b></td> <td><b><font color='#F33558'><?php echo $row_teamname->txtTeamName;?></font></b></td><?php } foreach($query_fn_ln as $row_f_l_name) {?> <td><?php echo $row_f_l_name->txtFirstname." ".$row_f_l_name->txtLastname;?></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><?php }?> </tr><?php } } } } } } } } }?> and in controller i have $projects_query = $this->admin_in_out_model->get_projects(); $tasks_query = $this->admin_in_out_model->get_systems(); $userteamtask = $this->admin_in_out_model->get_user_team_task(); $data['tasks_query'] = $tasks_query; $data['projects_query'] = $projects_query; $this->load->view('project_view',$data); but as you see I'm calling my model functions within the view how can i do something else to do this i mean not calling my model function in my view I have to add that, my model function have parameters these are the model functions: function get_projects() { $this -> db -> select('*'); $this -> db -> from('tbl_task'); $this -> db -> where('intInside','0'); $query = $this->db->get(); return $query->result(); } function get_systems() { $this -> db -> select('*'); $this -> db -> from('tbl_task '); $this -> db -> where('intInside <> ','0'); $query = $this->db->get(); return $query->result(); } function get_user_team_task_query($task_id)//gets information from tbl_userteamtask where the field intTaskID is equal to $task_id { $this -> db -> select('*'); $this -> db -> from('tbl_userteamtask'); $this -> db -> where('intTaskID',$task_id); $query_teamid = $this->db->get(); return $query_teamid->result(); } function get_user_team_task()//gets information from tbl_userteamtask where the field intTaskID is equal to $task_id { $this -> db -> select('*'); $this -> db -> from('tbl_userteamtask'); // $this -> db -> where('intTaskID',$task_id); $query_teamid = $this->db->get(); return $query_teamid->result(); } function get_team_name($query_teamid) { $this -> db -> select('*'); $this -> db -> from('tbl_team'); $this -> db -> where('intTeamID',$query_teamid); $query_teamname = $this->db->get(); return $query_teamname->result(); } function get_user_name($query_userid) { $this -> db -> select('*'); $this -> db -> from('tbl_user'); $this -> db -> where('intUserID',$query_userid); $query_username = $this->db->get(); return $query_username->result(); } function get_fn_ln_from_userid($selected_id) { $this -> db -> select('tbl_user.intUserID, tbl_user.intPersonID,tbl_person.intPersonID,tbl_person.txtFirstname, tbl_person.txtLastname'); $this -> db -> from('tbl_user , tbl_person'); $where = "tbl_user.intPersonID = tbl_person.intPersonID "; $this -> db -> where($where); $this -> db -> where('tbl_user.intUserID', $selected_id); $query = $this -> db -> get();//makes query from DB return $query->result(); } do I have to use subquery ? is this true? i mean can i do this? foreach( $data as $key => $each ) { $data[$key]['team_id'] = $this->get_user_team_task_query( $each['intTaskID'] ); foreach($data[$key]['team_id'] as $key_teamname => $each) { $data[$key_teamname]['team_name'] = $this->get_team_name( $each['intTeamID'] ); } } the model code: foreach( $data as $key => $each ) { $data[$key]['intTaskID'] = $each['intTaskID']; $data[$key]['team_id'] = $this->get_user_team_task_query( $each['intTaskID'] ); foreach($data[$key]['team_id'] as $key => $each) { $data[$key]['team_name'] = $this->get_team_name( $each['intTeamID'] ); #fetching of the teamname and saving in the array $data[$key]['user_name'] = $this->get_fn_ln_from_userid( $each['intUserID'] ); foreach($data[$key]['user_name'] as $key => $each) { $data[$key]['first_name'] = $each['txtFirstname'] ; $data[$key]['last_name'] = $each['txtLastname'] ; } $data[$key]['first_name'] = $data[$key]['first_name']; $data[$key]['last_name'] = $data[$key]['last_name']; } }

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• Why does my program not react to any arguments?

  - by Electric Coffee

  I have a simple test program in C++ that prints out attributes of a circle #include <iostream> #include <stdlib.h> #include "hidden_functions.h" // contains the Circle class using namespace std; void print_circle_attributes(float r) { Circle* c = new Circle(r); cout << "radius: " << c->get_radius() << endl; cout << "diameter: " << c->get_diameter() << endl; cout << "area: " << c->get_area() << endl; cout << "circumference: " << c->get_circumference() << endl; cout << endl; delete c; } int main(int argc, const char* argv[]) { float input = atof(argv[0]); print_circle_attributes(input); return 0; } when I run my program with the parameter 2.4 it outputs: radius: 0.0 diameter: 0.0 area: 0.0 circumference: 0.0 I've previously tested the program without the parameter, but simply using static values, and it ran just fine; so I know there's nothing wrong with the class I made... So what did I do wrong here? Note: the header is called hidden_functions.h because it served to test out how it would work if I had functions not declared in the header

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• What wrapper class in C++ should I use for automated resource management?

  - by Vilx-

  I'm a C++ amateur. I'm writing some Win32 API code and there are handles and weirdly compositely allocated objects aplenty. So I was wondering - is there some wrapper class that would make resource management easier? For example, when I want to load some data I open a file with CreateFile() and get a HANDLE. When I'm done with it, I should call CloseHandle() on it. But for any reasonably complex loading function there will be dozens of possible exit points, not to mention exceptions. So it would be great if I could wrap the handle in some kind of wrapper class which would automatically call CloseHandle() once execution left the scope. Even better - it could do some reference counting so I can pass it around in and out of other functions, and it would release the resource only when the last reference left scope. The concept is simple - but is there something like that in the standard library? I'm using Visual Studio 2008, by the way, and I don't want to attach a 3rd party framework like Boost or something.

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• Combine Arbitrary number of polygons together

  - by Jakobud

  I have an arbitrary number of polygons (hexes in this case) that are arranged randomly, but they are all touching another hex. Each individual hex has 6 x,y vertices. The vertex's are known for all the hexes. Can anyone point me in the direction of an algorithm that will combine all the hexes into a single polygon? Essentially I'm just looking for a function that spits out an array of vertex locations that are ordered in a way that when drawing lines from one to the next, it forms the polygon. This is my method so far: Create array of all the vertices for all the hexes. Determine the number of times a vertex occurs in the array If vertex is in the array 3+ times, delete the vertices from the array. If vertex is in the array 2 times, delete one of them. The next step is tricky though. I'm using canvas to draw out these polygons, which essentially involves drawing a line from one vertex to the next. So the order of the vertices in the final array is important. It can't be sorted arbitrarily. Also, I'm not looking for a "convex hull" algorithm, as that would not draw the polygon correctly. Are there any functions out there that do something like this? Am I on the right track or is there a better more efficient way?

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• which is better: a lying copy constructor or a non-standard one?

  - by PaulH

  I have a C++ class that contains a non-copyable handle. The class, however, must have a copy constructor. So, I've implemented one that transfers ownership of the handle to the new object (as below) class Foo { public: Foo() : h_( INVALID_HANDLE_VALUE ) { }; // transfer the handle to the new instance Foo( const Foo& other ) : h_( other.Detach() ) { }; ~Foo() { if( INVALID_HANDLE_VALUE != h_ ) CloseHandle( h_ ); }; // other interesting functions... private: /// disallow assignment const Foo& operator=( const Foo& ); HANDLE Detach() const { HANDLE h = h_; h_ = INVALID_HANDLE_VALUE; return h; }; /// a non-copyable handle mutable HANDLE h_; }; // class Foo My problem is that the standard copy constructor takes a const-reference and I'm modifying that reference. So, I'd like to know which is better (and why): a non-standard copy constructor: Foo( Foo& other ); a copy-constructor that 'lies': Foo( const Foo& other ); Thanks, PaulH

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• How best to implement support for multiple devices in a web application.

  - by Kabeer

  Hello. My client would like a business application to support 'every possible device'. The application in question is essentially a web application and 'every possible device', I believe encompasses mobile phones, netbooks, ipad, other browser supporting devices, etc. The application is somewhat complex w.r.t. the data it captures and other functions it performs (reporting). If I continue to honor increasing complexity in the application, I guess there are more chances of it not working on other devices. I'd like to know how web applications support multiple devices conventionally? Are there multiple versions of presentation layer (like many times I find m.website.com dedicated for mobile devices)? Further, if my application is to take advantage of Java Script, RIA (Flash, SilverLight) then what are the consequences and workarounds? Mine is a .Net based application and the stack also contains Ext JS Java Script library. While I would like to use it for sure, considering that I would be doing a lot of work in Java Script rather than HTML, this could be a problem. The answer to the above could be descriptive. If there is something already prescribed out there, please share the link(s). Thanks.

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• Binary serialization and deserialization without creating files (via strings)

  - by the_V

  Hi, I'm trying to create a class that will contain functions for serializing/deserializing objects to/from string. That's what it looks like now: public class BinarySerialization { public static string SerializeObject(object o) { string result = ""; if ((o.GetType().Attributes & TypeAttributes.Serializable) == TypeAttributes.Serializable) { BinaryFormatter f = new BinaryFormatter(); using (MemoryStream str = new MemoryStream()) { f.Serialize(str, o); str.Position = 0; StreamReader reader = new StreamReader(str); result = reader.ReadToEnd(); } } return result; } public static object DeserializeObject(string str) { object result = null; byte[] bytes = System.Text.Encoding.ASCII.GetBytes(str); using (MemoryStream stream = new MemoryStream(bytes)) { BinaryFormatter bf = new BinaryFormatter(); result = bf.Deserialize(stream); } return result; } } SerializeObject method works well, but DeserializeObject does not. I always get an exception with message "End of Stream encountered before parsing was completed". What may be wrong here?

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• Recommended approach for error handling with PHP and MYSQL

  - by iama

  I am trying to capture database (MYSQL) errors in my PHP web application. Currently, I see that there are functions like mysqli_error(), mysqli_errno() for capturing the last occurred error. However, this still requires me to check for error occurrence using repeated if/else statements in my php code. You may check my code below to see what I mean. Is there a better approach to doing this? (or) Should I write my own code to raise exceptions and catch them in one single place? What is the recommended approach? Also, does PDO raise exceptions? Thanks. function db_userexists($name, $pwd, &$dbErr) { $bUserExists = false; $uid = 0; $dbErr = ''; $db = new mysqli(SERVER, USER, PASSWORD, DB); if (!mysqli_connect_errno()) { $query = "select uid from user where uname = ? and pwd = ?"; $stmt = $db->prepare($query); if ($stmt) { if ($stmt->bind_param("ss", $name, $pwd)) { if ($stmt->bind_result($uid)) { if ($stmt->execute()) { if ($stmt->fetch()) { if ($uid) $bUserExists = true; } } } } if (!$bUserExists) $dbErr = $db->error(); $stmt->close(); } if (!$bUserExists) $dbErr = $db->error(); $db->close(); } else { $dbErr = mysqli_connect_error(); } return $bUserExists; }

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• Problem with incomplete input when using Attoparsec

  - by Dan Dyer

  I am converting some functioning Haskell code that uses Parsec to instead use Attoparsec in the hope of getting better performance. I have made the changes and everything compiles but my parser does not work correctly. I am parsing a file that consists of various record types, one per line. Each of my individual functions for parsing a record or comment works correctly but when I try to write a function to compile a sequence of records the parser always returns a partial result because it is expecting more input. These are the two main variations that I've tried. Both have the same problem. items :: Parser [Item] items = sepBy (comment <|> recordType1 <|> recordType2) endOfLine For this second one I changed the record/comment parsers to consume the end-of-line characters. items :: Parser [Item] items = manyTill (comment <|> recordType1 <|> recordType2) endOfInput Is there anything wrong with my approach? Is there some other way to achieve what I am attempting?

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• Preprocessor #define vs. function pointer - best practice?

  - by Dustin

  I recently started a small personal project (RGB value to BGR value conversion program) in C, and I realised that a function that converts from RGB to BGR can not only perform the conversion but also the inversion. Obviously that means I don't really need two functions rgb2bgr and bgr2rgb. However, does it matter whether I use a function pointer instead of a macro? For example: int rgb2bgr (const int rgb); /* * Should I do this because it allows the compiler to issue * appropriate error messages using the proper function name, * not to mention possible debugging benefits? */ int (*bgr2rgb) (const int bgr) = rgb2bgr; /* * Or should I do this since it is merely a convenience * and they're really the same function anyway? */ #define bgr2rgb(bgr) (rgb2bgr (bgr)) I'm not necessarily looking for a change in execution efficiency as it's more of a subjective question out of curiosity. I am well aware of the fact that type safety is neither lost nor gained using either method. Would the function pointer merely be a convenience or are there more practical benefits to be gained of which I am unaware?

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