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  • What is causing this template-related compile error? (c++)

    - by Setien
    When I try to compile this: #include <map> #include <string> template <class T> class ZUniquePool { typedef std::map< int, T* > ZObjectMap; ZObjectMap m_objects; public: T * Get( int id ) { ZObjectMap::const_iterator it = m_objects.find( id ); if( it == m_objects.end() ) { T * p = new T; m_objects[ id ] = p; return p; } return m_objects[ id ]; } }; int main( int argc, char * args ) { ZUniquePool< std::string > pool; return 0; } I get this: main.cpp: In member function ‘T* ZUniquePool<T>::Get(int)’: main.cpp:12: error: expected `;' before ‘it’ main.cpp:13: error: ‘it’ was not declared in this scope I'm using GCC 4.2.1 on Mac OS X. It works in VS2008. I'm wondering whether it might be a variation of this problem: http://stackoverflow.com/questions/1364837/why-doesnt-this-c-template-code-compile But as my error output is only partially similar, and my code works in VS2008, I am not sure. Can anyone shed some light on what I am doing wrong?

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  • I am trying to access the individual bytes in a floating point number and I am getting unexpected results

    - by oweinh
    So I have this so far: #include <iostream> #include <string> #include <typeinfo> using namespace std; int main () { float f = 3.45; // just an example fp# char* ptr = (char*)&f; // a character pointer to the first byte of the fp#? cout << int(ptr[0]) << endl; // these lines are just to see if I get what I cout << int(ptr[1]) << endl; // am looking for... I want ints that I can cout << int(ptr[2]) << endl; // otherwise manipulate. cout << int(ptr[3]) << endl; } the result is: -51 -52 92 64 so obviously -51 and -52 are not in the byte range that I would expect for a char... I have taken information from similar questions to arrive at this code and from all discussions, a conversion from char to int is straightforward. So why negative values? I am trying to look at a four-byte number, therefore I would expect 4 integers, each in the range 0-255. I am using Codeblocks 13.12 with gcc 4.8.1 with option -std=C++11 on a Windows 8.1 device.

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  • Add a smaller subView with new origin

    - by ReachWest
    I can't get my head around this - I know it must be simple.. I'm starting to feel pretty stupid. I have two viewControllers. MainViewController.h/m and LevelsViewController.h/m I want to add a subView from the LevelsViewController class and a view that is built in IB called levelsView. I am calling this from the MainViewController.m file. The levelsView is only 200x200 pixels and I want to offset it from the frame origin of the superView by x=140 pixels and y=50 pixels. I have this working - the view displays, but I can't figure out how to offset it. It only shows up at the 0,0 superView frame origin. (The superView shows below it, which is what I want). Here is the code I call in the method in the MainViewController.m that displays the levelsView.(I have commented out some of the things I have tried - but throws this error: error: request for member 'frame' in 'myLevelsView', which is of non-class type 'LevelsViewController*' ) - (void) displayLevelsPage { if (self.theLevelsView == nil) // Does not yet exist - therefore create { LevelsViewController * myLevelsView = [[LevelsViewController alloc] initWithNibName:@"levelsView" bundle:[NSBundle mainBundle]]; NSLog(@"NEW theLevelsView instance created!"); CGRect frame2 = CGRectMake(140, 50, 200, 200); //myLevelsView.frame = frame2; self.theLevelsView = myLevelsView; [myLevelsView release]; } [self.view addSubview: theLevelsView.view]; NSLog(@"Levels View has been activated"); } Any insight would be appreciated.

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  • Qt - 2 QMainWindow glued - Size of Layout

    - by user1773603
    I have a main window that I center this way in main.cpp : int main(int argc, char *argv[]) { QApplication app(argc, argv); QMainWindow *qmain = new QMainWindow; Ui_MainWindow ui; ui.setupUi(qmain); QRect r = qmain->geometry(); r.moveCenter(QApplication::desktop()->availableGeometry().center()); qmain->setGeometry(r); qmain->show(); return app.exec(); } In this "qmain" main window, I can create another QMainWindow and I try to make stick (or glue I don't know how to say) the two windows. Actually, I would like the right-top corner of the first one to be located at the left-top of the second one. For this, I use the following Ui_MainWindow's member function : void Ui_MainWindow::generate_IC() { qmenu = new QMainWindow; DiskMenu = new Ui_DiskGalMenu; DiskMenu->setupUi(qmenu); setInitialDiskMenuPosition(qmenu, this); qmenu->show(); } and the setInitialDiskMenuPosition : void Ui_MainWindow::setInitialDiskMenuPosition(QMainWindow *MainWindow, Ui_MainWindow *parent) { QSize size = parent->widget->size(); QDesktopWidget* desktop = QApplication::desktop(); int width = desktop->width(); int height = desktop->height(); int mw = size.width(); int mh = size.height(); int right = (width/2) + (mw/2); int top = (height/2) - (mh/2); MainWindow->move(right, top); } But the problem is that I don't get exactly what I want since the centralwidget size "parent- widget-size()" only returns the size of the widget and not the whole "qmain" parent window. So I have a light shift because the borders of the "qmain" window are not taken in account like it is shown below : If I could have access to the size of the whole parent window... If anyone could help me

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  • How to delete Drawn Line in java?

    - by Jeyjey
    Hello Folks, well this is my code: import javax.swing.; import javax.; import java.awt.; import java.awt.Color; import java.awt.Graphics.; import java.awt.event.*; import javax.swing.UIManager; public class SimpleGUI extends JFrame{ public SimpleGUI(){ this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) ; } public void go(){ Drawpanel = new Mypanel(); JFrame frame = new JFrame("Chasing Line"); frame.getContentPane().add(BorderLayout.CENTER, Drawpanel); frame.setSize(300,300); frame.setVisible(true); Drawpanel.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() { public void mouseMoved(java.awt.event.MouseEvent evt) { DrawpanelMouseMoved(evt); } }); } public void DrawpanelMouseMoved(java.awt.event.MouseEvent evt) { xpos=evt.getX(); ypos=evt.getY(); System.out.println("Coordinates : X :"+ xpos+"Y: "+ypos); Drawpanel.paintImage(xpos,ypos); } class Mypanel extends JPanel{ public void paintImage(int xpost,int ypost){ Graphics d = getGraphics(); d.setColor(Color.black); d.drawLine(xpost, 0, xpost, this.getHeight()); d.setColor(Color.red); d.drawLine(0, ypost, this.getWidth(),ypost); this.validate(); } } // end the inner class public static void main(String[] args){ try { UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); } catch(Exception e) { System.err.println("Look and feel not set"); } SimpleGUI win = new SimpleGUI(); win.go(); } Mypanel Drawpanel; private int xpos=0; private int ypos=0; } // close SimpleGUI class The problem is how can i delete the old lines?, i mea,make only the current x and y lines appear on the screen, make the intersection between both lines "follow" the mouse pointer. thanks for any reply.

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  • boost::function & boost::lambda - call site invocation & accessing _1 and _2 as the type

    - by John Dibling
    Sorry for the confusing title. Let me explain via code: #include <string> #include <boost\function.hpp> #include <boost\lambda\lambda.hpp> #include <iostream> int main() { using namespace boost::lambda; boost::function<std::string(std::string, std::string)> f = _1.append(_2); std::string s = f("Hello", "There"); std::cout << s; return 0; } I'm trying to use function to create a function that uses the labda expressions to create a new return value, and invoke that function at the call site, s = f("Hello", "There"); When I compile this, I get: 1>------ Build started: Project: hacks, Configuration: Debug x64 ------ 1>Compiling... 1>main.cpp 1>.\main.cpp(11) : error C2039: 'append' : is not a member of 'boost::lambda::lambda_functor<T>' 1> with 1> [ 1> T=boost::lambda::placeholder<1> 1> ] Using MSVC 9. My fundamental understanding of function and lambdas may be lacking. The tutorials and docs did not help so far this morning. How do I do what I'm trying to do?

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  • Internal typedef and circular dependency

    - by bcr
    I have two classes whose functions take typedefed pointers to eachother as return values and parameters. I.e.: class Segment; class Location : public Fwk::NamedInterface { public: // ===== Class Typedefs ===== typedef Fwk::Ptr<Location const> PtrConst; typedef Fwk::Ptr<Location> Ptr; // ===== Class Typedefs End ===== void segmentIs(Segment::Ptr seg); /* ... */ } and class Location; class Segment : public Fwk::NamedInterface { public: // ===== Class Typedefs ===== typedef Fwk::Ptr<Segment const> PtrConst; typedef Fwk::Ptr<Segment> Ptr; // ===== Class Typedefs End ===== void locationIs(Location::Ptr seg); /* ... */ } This understandably generated linker errors...which the forward declarations of the respective classes don't fix. How can I forward declare the Ptr and PtrConst typedefs while keeping these typedefs internal to the class (i.e. I would like to write Location::Ptr to refer to the location pointer type)? Thanks folks!

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  • Debugging a local SQL Server 2008 stored proceedure from Visual studio 2008

    - by Ricibob
    Hi all, There are a few posts about this question around but most concern remote debugging - here everything is on same machine. Visual studio 2008. I have a data connection to localhost SQL Server 2008 using Windows authentication with an admin account - this account is a member of sysadmin in SQL server. I double click stored proc and add a break point. I right click and select "Step into stored proceedure". I get the loathed and feared "Canceled by user." in output window. Does anyone know whats doing? Further - right clicking on the data connection shows both "Application debugging" and "Allow SQL/CLR Debugging". I have checked "Enable SQL Server debugging" on the properties of the C# client app. If run that in debug and try to step in to stored proc code "command.ExecuteNonQuery()" then the break points in the stored proc become disabled and are not pulled. After doing this once the right click on stored proc "Execute" and "Step into stored proceedure" are greyed/disabled. To get them back I have to restart visual studio (refresh connection doesn't do it). Any help much appreciated!! Cheers.

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  • multiple dependent android projects in eclipse

    - by lope
    Hi there! I just started to play with android dev and java+eclipse is pretty new to me. I managed to create simple project and run it on my device. Now I want to create simple game (more of them actually) and I would love to use shared code base for all of them (game loop, initialization, etc..). Problem is that I have no idea how to correctly do this. I created android project called engine with all basic stuff that I need and made it work on device. Now I tried to create another project in same workspace called mygame. Main class (activity) of mygame is MyGameApp which inherits from EngineApp (main activity of my engine project) which inherits from Activity. I added engine project into required projects in mygame build path tab in properties. Problem is that when I try to run this project it crashes on ClassNotFoundException trying to find my MyGameApp class. Any help (or pointer to some articles that explain how this is done) is greatly appreciated. few hours of googling didn't help much :/

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  • Conceptual data modeling: Is RDF the right tool? Other solutions?

    - by paprika
    I'm planning a system that combines various data sources and lets users do simple queries on these. A part of the system needs to act as an abstraction layer that knows all connected data sources: the user shouldn't [need to] know about the underlying data "providers". A data provider could be anything: a relational DBMS, a bug tracking system, ..., a weather station. They are hooked up to the query system through a common API that defines how to "offer" data. The type of queries a certain data provider understands is given by its "offer" (e.g. I know these entities, I can give you aggregates of type X for relationship Y, ...). My concern right now is the unification of the data: the various data providers need to agree on a common vocabulary (e.g. the name of the entity "customer" could vary across different systems). Thus, defining a high level representation of the entities and their relationships is required. So far I have the following requirements: I need to be able to define objects and their properties/attributes. Further, arbitrary relations between these objects need to be represented: a verb that defines the nature of the relation (e.g. "knows"), the multiplicity (e.g. 1:n) and the direction/navigability of the relation. It occurs to me that RDF is a viable option, but is it "the right tool" for this job? What other solutions/frameworks do exist for semantic data modeling that have a machine readable representation and why are they better suited for this task? I'm grateful for every opinion and pointer to helpful resources.

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  • Using memset on structures in C++

    - by garry
    Hey guys. I am working on fixing older code for my job. It is currently written in C++. They converted static allocation to dynamic but didn't edit the memsets/memcmp/memcpy. This is my first programming internship so bare with my newbe-like question. The following code is in C, but I want to have it in C++ ( I read that malloc isn't good practice in C++). I have two scenarios: First, we have f created. Then you use &f in order to fill with zero. The second is a pointer *pf. I'm not sure how to set pf to all 0's like the previous example in C++. Could you just do pf = new foo instead of malloc and then call memset(pf, 0, sizeof(foo))? struct foo { ... } f; memset( &f, 0, sizeof(f) ); //or struct foo { ... } *pf; pf = (struct foo*) malloc( sizeof(*pf) ); memset( pf, 0, sizeof(*pf) );

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  • Suggestions on Working with this Inherited Generic Method

    - by blu
    We have inherited a project that is a wrapper around a section of the core business model. There is one method that takes a generic, finds items matching that type from a member and then returns a list of that type. public List<T> GetFoos<T>() { List<IFoo> matches = Foos.FindAll( f => f.GetType() == typeof(T) ); List<T> resultList = new List<T>(); foreach (var match in matches) { resultList.Add((T)obj); } } Foos can hold the same object cast into various classes in inheritance hierarchy to aggregate totals differently for different UI presentations. There are 20+ different types of descendants that can be returned by GetFoos. The existing code basically has a big switch statement copied and pasted throughout the code. The code in each section calls GetFoos with its corresponding type. We are currently refactoring that into one consolidated area, but as we are doing that we are looking at other ways to work with this method. One thought was to use reflection to pass in the type, and that worked great until we realized the Invoke returned an object, and that it needed to be cast somehow to the List <T>. Another was to just use the switch statement until 4.0 and then use the dynamic language options. We welcome any alternate thoughts on how we can work with this method. I have left the code pretty brief, but if you'd like to know any additional details please just ask.

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  • When are temporaries created as part of a function call destroyed?

    - by Michael Mrozek
    Is a temporary created as part of an argument to a function call guaranteed to stay around until the called function ends, even if the temporary isn't passed directly to the function? There's virtually no chance that was coherent, so here's an example: class A { public: A(int x) : x(x) {printf("Constructed A(%d)\n", x);} ~A() {printf("Destroyed A\n");} int x; int* y() {return &x;} }; void foo(int* bar) { printf("foo(): %d\n", *bar); } int main(int argc, char** argv) { foo(A(4).y()); } If A(4) were passed directly to foo it would definitely not be destroyed until after the foo call ended, but instead I'm calling a method on the temporary and losing any reference to it. I would instinctively think the temporary A would be destroyed before foo even starts, but testing with GCC 4.3.4 shows it isn't; the output is: Constructed A(4) foo(): 4 Destroyed A The question is, is GCC's behavior guaranteed by the spec? Or is a compiler allowed to destroy the temporary A before the call to foo, invaliding the pointer to its member I'm using?

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  • Why is the operation address incremented by two?

    - by Gavin Jones
    I am looking at a Javascript emulator of a NES to try and understand how it works. On this line: addr = this.load(opaddr+2); The opcode is incremented by two. However, the documentation (see appendix E) I'm reading says: Zero page addressing uses a single operand which serves as a pointer to an address in zero page ($0000-$00FF) where the data to be operated on can be found. By using zero page addressing, only one byte is needed for the operand, so the instruction is shorter and, therefore, faster to execute than with addressing modes which take two operands. An example of a zero page instruction is AND $12. So if the operand's argument is only one byte, shouldn't it appear directly after it, and be + 1 instead of + 2? Why +2? This is how I think it works, which may be incorrect. Suppose our memory looks like: ------------------------- | 0 | 1 | 2 | 3 | 4 | 5 | <- index ------------------------- | a | b | c | d | e | f | <- memory ------------------------- ^ \ PC and our PC is 0, pointing to a. For this cycle, we say that the opcode: var pc= 0; //for example's sake var opcode= memory[pc]; //a So shouldn't the first operand be the next slot, i.e. b? var first_operand = memory[pc + 1]; //b

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  • Trying to overload + operator

    - by FrostyStraw
    I cannot for the life of me understand why this is not working. I am so confused. I have a class Person which has a data member age, and I just want to add two people so that it adds the ages. I don't know why this is so hard, but I'm looking for examples and I feel like everyone does something different, and for some reason NONE of them work. Sometimes the examples I see have two parameters, sometimes they only have one, sometimes the parameters are references to the object, sometimes they're not, sometimes they return an int, sometimes they return a Person object. Like..what is the most normal way to do it? class Person { public: int age; //std::string haircolor = "brown"; //std::string ID = "23432598"; Person(): age(19) {} Person operator+(Person&) { } }; Person operator+(Person &obj1, Person &obj2){ Person sum = obj1; sum += obj2; return sum; } I really feel like overloading a + operator should seriously be the easiest thing in the world except I DON'T KNOW WHAT I AM DOING. I don't know if I'm supposed to create the overload function inside the class, outside, if it makes a difference, why if I do it inside it only allows one parameter, I just honestly don't get it.

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  • pass parameter from $.post() callback to outer variable

    - by Nazmin
    basically i want to hold a parameter that retrieve value from $.post() call like this: init = function(){ var lastpage = getLastPage(); } function getLastPage(){ $.post("getInfo.php",{ last: "yes" }, function(data){ setLast(data.last); },'json'); return function setLast(data){ return data; } } so when reach at last post (last page) i should check with lastpage variable that has a value returned from getLastPage() function. I'm pretty blur with javascript pointer and all. Please help guys. update (20/4/2010): I've done the other way around, like this: init = function(){ getLastPage(); if((page+1) == $("#lastpage").val()){ alert("this is last post"); }else{ page++; //get info and display to the page here } } function getLastPage(){ $.post("getInfo.php",{ last: "yes" }, function(data){ $("#lastpage").val(data.last); },'json'); } first run the function to temporarily store the value in hidden input tag (lastpage) and then grab the value again to check it whenever i click forward button. if you all have more appropriate way please tell me.

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  • Why does this CSS button mess with <a> tags?

    - by Ian McCullough
    Here is my CSS button { border: 0 none; cursor: pointer; padding: 0 15px 0 0; text-align: center; height: 30px; line-height: 30px; width: auto; } button a { color:white; text-decoration:none; } button.rounded { background: transparent url(/images/button/btn_right.png) no-repeat scroll right top; clear: left; font-size: 0.8em; } button span { display: block; padding: 0 0 0 15px; position: relative; white-space: nowrap; height: 30px; line-height: 30px; } button.rounded span { background: transparent url(/images/button/btn_left.png) no-repeat scroll left top; color: #FFFFFF; } button.rounded:hover { background-position: 100% -30px; } button.rounded:hover span { background-position: 0% -30px; } button::-moz-focus-inner { border: none; } Here is the code for my "button" with a link in it. <button class="rounded"><span><a href="profile.php">Profile</a></span></button> The issue is it does not link to the href when i click on it. Anyone know why?

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  • Sending a message to nil?

    - by Ryan Delucchi
    As a Java developer who is reading Apple's Objective-C 2.0 documentation: I wonder as to what sending a message to nil means - let alone how it is actually useful. Taking an excerpt from the documentation: There are several patterns in Cocoa that take advantage of this fact. The value returned from a message to nil may also be valid: If the method returns an object, any pointer type, any integer scalar of size less than or equal to sizeof(void*), a float, a double, a long double, or a long long, then a message sent to nil returns 0. If the method returns a struct, as defined by the Mac OS X ABI Function Call Guide to be returned in registers, then a message sent to nil returns 0.0 for every field in the data structure. Other struct data types will not be filled with zeros. If the method returns anything other than the aforementioned value types the return value of a message sent to nil is undefined. Has Java rendered my brain incapable of grokking the explanation above? Or is there something that I am missing that would make this as clear as glass? Note: Yes, I do get the idea of messages/receivers in Objective-C, I am simply confused about a receiver that happens to be nil.

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  • Determining difference in timestamps for two values in the same MySQL table

    - by JayRizzo03
    I am relatively new to programming in PHP, so I apologize if this is a rather simple question. I have a MySQL database table called MachineReports that contains the following values: ReportNum(primary key, auto increment), MachineID and Timestamp Here is some example data: |ReportNum | MachineID | Timestamp | |1 | AD3203 | 2012-11-18 06:32:28| |2 | AD3203 | 2012-11-19 04:00:15| |3 | BC4300 | 2012-11-19 04:00:15| What I am attempting to do is find the difference in timestamps in seconds for each machine ID by iterating over each row set. I am getting stuck on the best way to do this, however. Here is the code I've written so far: <?php include '../dbconnect/dbconnect.php'; $machineID=[]; //Get a list of all MachineIDs in the database foreach($dbh->query('SELECT DISTINCT(MachineID) FROM MachineReports') as $row) { array_push($machineID, $row[0]); } for($i=0;$i<count($machineID);$i++){ foreach($dbh->query("SELECT MachineID FROM MachineReports WHERE MachineID='$machineID[$i]' ORDER BY MachineID") as $row) { //code to associate each machineID with two time stamps goes here } } ? This code just lists out the contents of the table row by row. My ultimate goal is to find the difference in timestamps for a certain MachineID. One of the things I've considered is using a multidimensional array in php - using the $machineID as the key and then storing the timestamp inside the array the key points to. However, I'm uncertain how to do that since my query parses row by row. I have quite a few questions. 1) Is this the most efficient way to be doing this? I suspect my database table design may not be the best. 2)What would be the best way to determine the difference in timestamps for a certain machineID? Even just a pointer to a topic that would prompt me to think about this in a different way would be helpful - I'm not afraid to do research. Thanks!

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  • geb StaleElementReferenceException

    - by Brian Mortenson
    I have just started using geb with webdriver for automating testing. As I understand it, when I define content on a page, the page element should be looked up each time I invoke a content definition. //In the content block of SomeModule, which is part of a moduleList on the page: itemLoaded { waitFor{ !loading.displayed } } loading { $('.loading') } //in the page definition moduleItems {index -> moduleList SomeModule, $("#module-list > .item"), index} //in a test on this page def item = moduleItems(someIndex) assert item.itemLoaded So in this code, I think $('.loading') should be called repeatedly, to find the element on the page by its selector, within the context of the module's base element. Yet I sometimes get a StaleElementReference exception at this point. As far as I can tell, the element does not get removed from the page, but even if it does, that should not produce this exception unless $ is doing some caching behind the scenes, but if that were the case it would cause all sorts of other problems. Can someone help me understand what's happening here? Why is it possible to get a StaleElementReferenceException while looking up an element? A pointer to relevant documentation or geb source code would be useful as well.

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  • Looking for something to add some standard rules for my c++ project.

    - by rkb
    Hello all, My team is developing a C++ project on linux. We use vim as editor. I want to enforce some code standard rules in our team in such a way that if the code is not in accordance with it, some sort of warning or error will be thrown when it builds or compiles. Not necessarily it builds but at least I can run some plugin or tools on that code to make sure it meets the standard. So that before committing to svn everyone need to run the code through some sort of plugin or script and make sure it meets the requirement and then only he/she can commit. Not sure if we can add some rules to vim, if there are any let me know about it. For eg. In our code standards all the member variables and private functions should start with _ class A{ private: int _count; float _amount; void _increment_count(){ ++_count; } } So I want to throw some warning or error or some sort of messages for this class if the variables are declared as follows. class A{ private: int count; float amount; void increment_count(){ ++_count; } } Please note that warning and error are not from compiler becoz program is still valid. Its from the tool I want to use so that code goes to re-factoring but still works fine on the executable side. I am looking for some sort of plugin or pre parsers or scripts which will help me in achieving all this. Currently we use svn; just to anser the comment.

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  • C++: getting the address of the start of an std::vector ?

    - by shoosh
    Sometimes it is useful to use the starting address of an std::vector and temporarily treat that address as the address of a regularly allocated buffer. For instance replace this: char* buf = new char[size]; fillTheBuffer(buf, size); useTheBuffer(buf, size); delete[] buf; With This: vector<char> buf(size); fillTheBuffer(&buf[0], size); useTheBuffer(&buf[0], size); The advantage of this is of course that the buffer is deallocated automatically and I don't have to worry about the delete[]. The problem I'm having with this is when size == 0. In that case the first version works ok. An empty buffer is "allocated" and the subsequent functions do nothing size they get size == 0. The second version however fails if size == 0 since calling buf[0] may rightly contain an assertion that 0 < size. So is there an alternative to the idiom &buf[0] that returns the address of the start of the vector even if the vector is empty? I've also considered using buf.begin() but according to the standard it isn't even guaranteed to return a pointer.

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  • const object in c++

    - by Codenotguru
    I have a question on constant objects. In the following program: class const_check{ int a; public: const_check(int i); void print() const; void print2(); }; const_check::const_check(int i):a(i) {} void const_check::print() const { int a=19; cout<<"The value in a is:"<<a; } void const_check::print2() { int a=10; cout<<"The value in a is:"<<a; } int main(){ const_check b(5); const const_check c(6); b.print2(); c.print(); } void print() is constant member function of the class const_check, so according to the definition of constants if any attempt to change int a it should result in an error but the program works fine for me.I think i am having some confusion here, can anybody tell me why the compiler is not flagging it as an error??

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  • How do virtual destructors work?

    - by Jack
    I am using gcc. I am aware how the virtual destructors solve the problem when we destroy a derived class object pointed by a base class pointer. I want to know how do they work? class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; int main() { A * a = new B(); delete a; getch(); return 0; } When I change A's destructor to a virtual function, the problem is solved. What is the inner working for this. Why do I make A's destructor virtual.

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  • C++ Template Classes and Copy Construction

    - by themoondothshine
    Is there any way I can construct an new object from the given object if the template parameters of both objects are identical at run-time? For example: I have a template class with the declaration: template<typename _Type1, typename _Type2> class Object; Next, I have two instantiations of the template: template class Object<char, int>; template class Object<wchar_t, wint_t>; Now, I want to write a member function such as: template<typename _Type1, typename _Type2> Object<char, int> Object<_Type1, _Type2>::toCharObject() { if(__gnu_cxx::__are_same<_Type1, char>::__value) return *this; else { //Perform some kind of conversion and return an Object<char, int> } } I have tried a couple of techniques, such as using __gnu_cxx::__enable_if<__gnu_cxx::__are_same<_Type1, char>::__value, _Type1>::__type in a copy constructor for the Oject class, but I keep running into the error: error: conversion from ‘Object<wchar_t, wint_t>’ to non-scalar type ‘Object<char, int>’ requested Is there no way I can do this? Any help will be greatly appreciated!

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