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• Turing Model Vs Von Neuman model

  - by Santhosh

  First some background (based on my understanding).. The Von-Neumann architecture describes the stored-program computer where instructions and data are stored in memory and the machine works by changing it's internal state, i.e an instruction operated on some data and modifies the data. So inherently, there is state msintained in the system. The Turing machine architecture works by manipulating symbols on a tape. i.e A tape with infinite number of slots exists, and at any one point in time, the Turing machine is in a particular slot. Based on the symbol read at that slot, the machine change the symbol and move to a different slot. All of this is deterministic. My questions are Is there any relation between these two models (Was the Von Neuman model based on or inspired by the Turing model)? Can we say that Turing model is a superset of Von Newman model? Does functional Programming fit into Turing model. If so how? (I assume FP does not lend itself nicely to the Von Neuman model)

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• Coupling between controller and view

  - by cheez

  The litmus test for me for a good MVC implementation is how easy it is to swap out the view. I've always done this really badly due to being lazy but now I want to do it right. This is in C++ but it should apply equally to non-desktop applications, if I am to believe the hype. Here is one example: the application controller has to check some URL for existence in the background. It may connect to the "URL available" event (using Boost Signals) as follows: BackgroundUrlCheckerThread(Controller & controller) { // ... signalUrlAvailable.connect( boost::bind(&Controller::urlAvailable,&controller,_1)) } So what does Controller::urlAvailable look like? Here is one possibility: void Controller::urlAvailable(Url url) { if(!view->askUser("URL available, wanna download it?")) return; else // Download the url in a new thread, repeat } This, to me, seems like a gross coupling of the view and the controller. Such a coupling makes it impossible to implement the view when using the web (coroutines aside.) Another possibility: void Controller::urlAvailable(Url url) { urlAvailableSignal(url); // Now, any view interested can do what it wants } I'm partial to the latter but it appears that if I do this there will be: 40 billion such signals. The application controller can get huge for a non-trivial application A very real possibility that a given view accidentally ignores some signals (APIs can inform you at link-time, but signals/slots are run-time) Thanks in advance.

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• Sending custom PyQt signals?

  - by Enfors

  I'm practicing PyQt and (Q)threads by making a simple Twitter client. I have two Qthreads. Main/GUI thread. Twitter fetch thread - fetches data from Twitter every X minutes. So, every X minutes my Twitter thread downloads a new set of status updates (a Python list). I want to hand this list over to the Main/GUI thread, so that it can update the window with these statuses. I'm assuming that I should be using the signal / slot system to transfer the "statuses" Python list from the Twitter thread, to the Main/GUI thread. So, my question is twofold: How do I send the statuses from the Twitter thread? How do I receive them in the Main/GUI thread? As far as I can tell, PyQt can by default only send PyQt-objects via signals / slots. I think I'm supposed to somehow register a custom signal which I can then send, but the documentation on this that I've found is very unclear to a newbie like me. I have a PyQt book on order, but it won't arrive in another week, and I don't want to wait until then. :-) I'm using PyQt 4.6-1 on Ubuntu Update: This is an excert from the code that doesn't work. First, I try to "connect" the signal ("newStatuses", a name I just made up) to the function self.update_tweet_list in the Main/GUI thread: QtCore.QObject.connect(self.twit_in, QtCore.SIGNAL("newStatuses (statuses)"), self.update_tweet_list) Then, in the Twitter thread, I do this: self.emit(SIGNAL("newStatuses (statuses)"), statuses) When this line is called, I get the following message: QObject::connect: Cannot queue arguments of type 'statuses' (Make sure 'statuses' is registered using qRegisterMetaType().) I did a search for qRegisterMetaType() but I didn't find anything relating to Python that I could understand.

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• Is it possible that a single-threaded program is executed simultaneously on more than one CPU core?

  - by Wolfgang Plaschg

  When I run a single-threaded program that i have written on my quad core Intel i can see in the Windows Task Manager that actually all four cores of my CPU are more or less active. One core is more active than the other three, but there is also activity on those. There's no other program (besided the OS kernel of course) running that would be plausible for that activitiy. And when I close my program all activity an all cores drops down to nearly zero. All is left is a little "noise" on the cores, so I'm pretty sure all the visible activity comes directly or indirectly (like invoking system routines) from my program. Is it possible that the OS or the cores themselves try to balance some code or execution on all four cores, even it's not a multithreaded program? Do you have any links that documents this technique? Some infos to the program: It's a console app written in Qt, the Task Manager states that only one thread is running. Maybe Qt uses threads, but I don't use signals or slots, nor any GUI. Link to Task Manager screenshot: http://img97.imageshack.us/img97/6403/taskmanager.png This question is language agnostic and not tied to Qt/C++, i just want to know if Windows or Intel do to balance also single-threaded code on all cores. If they do, how does this technique work? All I can think of is, that kernel routines like reading from disk etc. is scheduled on all cores, but this won't improve performance significantly since the code still has to run synchronous to the kernel api calls. EDIT Do you know any tools to do a better analysis of single and/or multi-threaded programs than the poor Windows Task Manager?

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• Good patterns for loose coupling in Java?

  - by Eye of Hell

  Hello. I'm new to java, and while reading documentation so far i can't find any good ways for programming with loose coupling between objects. For majority of languages i know (C++, C#, python, javascript) i can manage objects as having 'signals' (notification about something happens/something needed) and 'slots' (method that can be connected to signal and process notification/do some work). In all mentioned languages i can write something like this: Object1 = new Object1Class(); Object2 = new Object2Class(); Connect( Object1.ItemAdded, Object2.OnItemAdded ); Now if object1 calls/emits ItemAdded, the OnItemAdded method of Object2 will be called. Such loose coupling technique is often referred as 'delegates', 'signal-slot' or 'inversion of control'. Compared to interface pattern, technique mentioned don't need to group signals into some interfaces. Any object's methods can be connected to any delegate as long as signatures match ( C++Qt even extends this by allowing only partial signature match ). So i don't need to write additional interface code for each methods / groups of methods, provide default implementation for interface methods not used etc. And i can't see anything like this in Java :(. Maybe i'm looking a wrong way?

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• How can I test that my hash function is good in terms of max-load?

  - by philcolbourn

  I have read through various papers on the 'Balls and Bins' problem and it seems that if a hash function is working right (ie. it is effectively a random distribution) then the following should/must be true if I hash n values into a hash table with n slots (or bins): Probability that a bin is empty, for large n is 1/e. Expected number of empty bins is n/e. Probability that a bin has k collisions is <= 1/k!. Probability that a bin has at least k collisions is <= (e/k)**k. These look easy to check. But the max-load test (the maximum number of collisions with high probability) is usually stated vaguely. Most texts state that the maximum number of collisions in any bin is O( ln(n) / ln(ln(n)) ). Some say it is 3*ln(n) / ln(ln(n)). Other papers mix ln and log - usually without defining them, or state that log is log base e and then use ln elsewhere. Is ln the log to base e or 2 and is this max-load formula right and how big should n be to run a test? This lecture seems to cover it best, but I am no mathematician. http://pages.cs.wisc.edu/~shuchi/courses/787-F07/scribe-notes/lecture07.pdf BTW, with high probability seems to mean 1 - 1/n.

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• google maps not showing actual map and postcode

  - by Andy

  Im trying to pass a dynamically generated postode to a page. But currently its not showing the map correctly. Any ideas? Heres my head tag <script src="http://www.google.com/jsapi?key=ABQIAAAANQzcZVPOkiHWMZO3zxREGRSlIja3KBL7jZ08tky_uJrV3vVYdxTCwTHJPA2Vn06DLdnCWvRW_w7VYQ" type="text/javascript"></script> <script language="Javascript" type="text/javascript"> var localSearch; var map; var icon; var addressMarkerOptions; google.load("search", "1"); google.load("maps", "2"); google.setOnLoadCallback(initialize); function initialize() { localSearch = new GlocalSearch(); icon = new GIcon(G_DEFAULT_ICON); addressMarkerOptions = { icon:icon , draggable: false}; map = new GMap2(document.getElementById("map")); map.addControl(new GLargeMapControl()); map.addControl(new GMapTypeControl()); plotAddress("OX4 1FJ"); } /** * This takes either a postcode or an address string * */ function plotAddress(address) { localSearch.setSearchCompleteCallback(null, function() { if (localSearch.results[0]) { var resultLat = localSearch.results[0].lat; var resultLng = localSearch.results[0].lng; var point = new GLatLng(resultLat,resultLng); var marker = new GMarker(point, addressMarkerOptions); map.addOverlay(marker); map.setCenter(point, 5, G_NORMAL_MAP); } else { alert('address not found'); } }); localSearch.execute(address + ", UK"); } </script> It slots into the code below: <div id="map">Loading...</div>

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• How to delete a QProcess instance correctly?

  - by Kopfschmerzen

  Hi everyone! I have a class looking like this: class FakeRunner : public QObject { Q_OBJECT private: QProcess* proc; public: FakeRunner(); int run() { if (proc) return -1; proc = new QProcess(); QStringList args; QString programName = "fake.exe"; connect(comp, SIGNAL(started()), this, SLOT(procStarted())); connect(comp, SIGNAL(error(QProcess::ProcessError)), this, SLOT(procError(QProcess::ProcessError))); connect(comp, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(procFinished(int, QProcess::ExitStatus))); proc->start(programName, args); return 0; }; private slots: void procStarted() {}; void procFinished(int, QProcess::ExitStatus) {}; void procError(QProcess::ProcessError); } Since "fake.exe" does not exist on my system, proc emits the error() signal. If I handle it like following, my program crashes: void FakeRunner::procError(QProcess::ProcessError rc) { delete proc; proc = 0; } It works well, though, if I don't delete the pointer. So, the question is how (and when) should I delete the pointer to QProcess? I believe I have to delete it to avoid a memory leak. FakeRunner::run() can be invoked many times, so the leak, if there is one, will grow. Thanks!

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• What are the alternatives to public fields?

  - by James

  I am programming a game in java, and as the question title suggestions i am using public fields in my classes. (for the time being) From what i have seen public fields are bad and i have some understanding why. (but if someone could clarify why you should not use them, that would be appreciated) The thing is that also from what i have seen, (and it seems logical) is that using private fields, but using getters and setters to access them is also not good as it defeats the point of using private fields in the first place. So, my question is, what are the alternatives? or do i really have to use private fields with getters and setters? For reference here is one of my classes, and some of its methods. I will elaborate more if needs be. //The player's fields. public double health; public String name; public double goldCount; public double maxWeight; public double currentWeight; public double maxBackPckSlts; public double usedBackPckSlts; // The current back pack slots in use public double maxHealth; // Maximum amount of health public ArrayList<String> backPack = new ArrayList<String>(); //This method happens when ever the player dynamically takes damage(i.e. when it is not scripted for the player to take damage. //Parameters will be added to make it dynamic so the player can take any spread of damage. public void beDamaged(double damage) { this.health -= damage; if (this.health < 0) { this.health = 0; } } public void gainHealth(double gainedHp) { this.health += gainedHp; if (this.health > this.maxHealth) { this.health = this.maxHealth; } }

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• Getting exception when trying to monkey patch pymongo.connection._Pool

  - by Creotiv

  I use pymongo 1.9 on Ubuntu 10.10 with python 2.6.6 When i trying to monkey patch pymongo.connection._Pool i'm getting error on connection: AutoReconnect: could not find master/primary But when i change _Pool class in pymongo.connection module, it work pretty fine. Even if i copy _Pool implementation from pymongo.connection module and will try to monkey patch by the same code, it still giving same exception. I need to remove threading.local from _Pool class, because i use gevent and i need to implement Pool for all mongo connections(for all threads). I use this code: import pymongo class GPool: """A simple connection pool. Uses thread-local socket per thread. By calling return_socket() a thread can return a socket to the pool. Right now the pool size is capped at 10 sockets - we can expose this as a parameter later, if needed. """ # Non thread-locals __slots__ = ["sockets", "socket_factory", "pool_size","sock"] #sock = None def __init__(self, socket_factory): self.pool_size = 10 if not hasattr(self,"sock"): self.sock = None self.socket_factory = socket_factory if not hasattr(self, "sockets"): self.sockets = [] def socket(self): # we store the pid here to avoid issues with fork / # multiprocessing - see # test.test_connection:TestConnection.test_fork for an example # of what could go wrong otherwise pid = os.getpid() if self.sock is not None and self.sock[0] == pid: return self.sock[1] try: self.sock = (pid, self.sockets.pop()) except IndexError: self.sock = (pid, self.socket_factory()) return self.sock[1] def return_socket(self): if self.sock is not None and self.sock[0] == os.getpid(): # There's a race condition here, but we deliberately # ignore it. It means that if the pool_size is 10 we # might actually keep slightly more than that. if len(self.sockets) < self.pool_size: self.sockets.append(self.sock[1]) else: self.sock[1].close() self.sock = None pymongo.connection._Pool = GPool

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• Common lisp, CFFI, and instantiating c structs

  - by andrew

  Hi, I've been on google for about, oh, 3 hours looking for a solution to this "problem." I'm trying to figure out how to instantiate a C structure in lisp using CFFI. I have a struct in c: struct cpVect{cpFloat x,y;} Simple right? I have auto-generated CFFI bindings (swig, I think) to this struct: (cffi:defcstruct #.(chipmunk-lispify "cpVect" 'classname) (#.(chipmunk-lispify "x" 'slotname) :double) (#.(chipmunk-lispify "y" 'slotname) :double)) This generates a struct "VECT" with slots :X and :Y, which foreign-slot-names confirms (please note that I neither generated the bindings or programmed the C library (chipmunk physics), but the actual functions are being called from lisp just fine). I've searched far and wide, and maybe I've seen it 100 times and glossed over it, but I cannot figure out how to create a instance of cpVect in lisp to use in other functions. Note the function: cpShape *cpPolyShapeNew(cpBody *body, int numVerts, cpVect *verts, cpVect offset) Takes not only a cpVect, but also a pointer to a set of cpVects, which brings me to my second question: how do I create a pointer to a set of structs? I've been to http://common-lisp.net/project/cffi/manual/html_node/defcstruct.html and tried the code, but get "Error: Unbound variable: PTR" (I'm in Clozure CL), not to mention that looks to only return a pointer, not an instance. I'm new to lisp, been going pretty strong so far, but this is the first real problem I've hit that I can't figure out. Thanks!

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• Why is creating a ring buffer shared by different processes so hard (in C++), what I am doing wrong?

  - by recipriversexclusion

  I am being especially dense about this but it seems I'm missing an important, basic point or something, since what I want to do should be common: I need to create a fixed-size ring buffer object from a manager process (Process M). This object has write() and read() methods to write/read from the buffer. The read/write methods will be called by independent processes (Process R and W) I have implemented the buffer, SharedBuffer<T&>, it allocates buffer slots in SHM using boost::interprocess and works perfectly within a single process. I have read the answers to this question and that one on SO, as well as asked my own, but I'm still in the dark about how to have different processes access methods from a common object. The Boost doc has an example of creating a vector in SHM, which is very similar to what I want, but I want to instantiate my own class. My current options are: Use placement new, as suggested by Charles B. to my question; however, he cautions that it's not a good idea to put non-POD objects in SHM. But my class needs the read/write methods, how can I handle those? Add an allocator to my class definition, e.g. have SharedBuffer<T&, Alloc> and proceed similarly to the vector example given in boost. This sounds really complicated. Change SharedBuffer to a POD class, i.e. get rid of all the methods. But then how to synchronize reading and writing between processes? What am I missing? Fixed-length ring buffers are very common, so either this problem has a solution or else I'm doing something wrong.

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• Python script to calculate aded combinations from a dictionary

  - by dayde

  I am trying to write a script that will take a dictionary of items, each containing properties of values from 0 - 10, and add the various elements to select which combination of items achieve the desired totals. I also need the script to do this, using only items that have the same "slot" in common. For example: item_list = { 'item_1': {'slot': 'top', 'prop_a': 2, 'prop_b': 0, 'prop_c': 2, 'prop_d': 1 }, 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 }, 'item_3': {'slot': 'top', 'prop_a': 2, 'prop_b': 5, 'prop_c': 2, 'prop_d':-2 }, 'item_4': {'slot': 'mid', 'prop_a': 5, 'prop_b': 5, 'prop_c':-5, 'prop_d': 0 }, 'item_5': {'slot': 'mid', 'prop_a':10, 'prop_b': 0, 'prop_c':-5, 'prop_d': 0 }, 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 }, 'item_7': {'slot': 'bot', 'prop_a': 1, 'prop_b': 3, 'prop_c':-4, 'prop_d': 4 }, 'item_8': {'slot': 'bot', 'prop_a': 2, 'prop_b': 2, 'prop_c': 0, 'prop_d': 0 }, 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 }, } The script would then need to select which combinations from the "item_list" dict that using 1 item per "slot" that would achieve a desired result when added. For example, if the desired result was: 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0, the script would select 'item_2', 'item_6', and 'item_9', along with any other combination that worked. 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 } 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 } 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 } 'total': 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0 Any ideas how to accomplish this? It does not need to be in python, or even a thorough script, but just an explanation on how to do this in theory would be enough for me. I have tried working out looping through every combination, but that seems to very quickly get our of hand and unmanageable. The actual script will need to do this for about 1,000 items using 20 different "slots", each with 8 properties. Thanks for the help!

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• How can I check if the mouse button is released, and THEN execute a procedure once in Borland Pascal

  - by Robert

  Hi! I use Borland Pascal 7.0, and I would like to make a slots game (If 3 random numbers are the same, you win). The problem is that when I click on the start (Inditas) button on the menu, the procedure executes many times until I release the mouse button. I was told that I should check if the mouse button is released before executing the procedure once. How can I do that? Here's what the menu looks like: procedure eger; begin; mouseinit; mouseon; menu; repeat getmouse(m); if (m.left) and (m.x60) ANd (m.x<130) and (m.y120) and (m.y<150) then teglalap(90,90,300,300,blue); if (m.left) and (m.x60) AND (m.x<130) and (m.y160) and (m.y<190) then jatek(a,b,c,coin,coins); until ((m.left) and (m.x60) ANd (m.x<130) and (m.y240) and (m.y<270)); end; Thanks, Robert

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• Qt cross thread call

  - by QLatvia

  I have a Qt/C++ application, with the usual GUI thread, and a network thread. The network thread is using an external library, which has its own select() based event loop... so the network thread isn't using Qt's event system. At the moment, the network thread just emit()s signals when various events occur, such as a successful connection. I think this works okay, as the signals/slots mechanism posts the signals correctly for the GUI thread. Now, I need for the network thread to be able to call the GUI thread to ask questions. For example, the network thread may require the GUI thread to request put up a dialog, to request a password. Does anyone know a suitable mechanism for doing this? My current best idea is to have the network thread wait using a QWaitCondition, after emitting an object (emit passwordRequestedEvent(passwordRequest);. The passwordRequest object would have a handle on the particular QWaitCondition, and so can signal it when a decision has been made.. Is this sort of thing sensible? or is there another option?

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• ISO C++ forbids declaration of 'QPushButton' with no type in QT Creator

  - by Mohit Deshpande

  I am running QT Creator on a Linux Ubuntu 9.10 machine. I just got started with QT Creator, and I was going through the tutorials when this error popped up while I was trying to build my project: "ISO C++ forbids declaration of 'QPushButton' with no type". This problem appears in my header file: #ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QtGui/QWidget> namespace Ui { class MainWindow; } class MainWindow : public QWidget { Q_OBJECT public: MainWindow(QWidget *parent = 0); ~MainWindow(); public slots: void addContact(); void submitContact(); void cancel(); private: Ui::MainWindow *ui; QPushButton *addButton; QPushButton *submitButton; QPushButton *cancelButton; QLineEdit *nameLine; QTextEdit *addressText; QMap<QString, QString> contacts; QString oldName; QString oldAddress; }; #endif // MAINWINDOW_H

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• QT NOOB: Add action handler for multiple objects of same type.

  - by what

  I have a simple QT application with 10 radio buttons with names radio_1 through radio_10. It is a ui called Selector, and is part of a class called TimeSelector In my header file for this design, i have this: //! [1] class TimeSelector : public QWidget { Q_OBJECT public: TimeSelector(QWidget *parent = 0); private slots: //void on_inputSpinBox1_valueChanged(int value); //void on_inputSpinBox2_valueChanged(int value); private: Ui::Selector ui; }; //! [1] the commented out void_on_inputSpinBox1_valueChanged(int value) is from the tutorial for the simple calculator. I know i can do: void on_radio_1_valueChanged(int value); but I would need 10 functions. I want to be able to make one function that works for everything, and lets me pass in maybe a name of the radio button that called it, or a reference to the radio button so i can work with it and determine who it was. I am very new to QT but this seems like it should be very basic and doable, thanks.

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• one key multiple values from different sources c#

  - by user2964034

  I am trying to make a c# program that will compare two files for me, and tell me the differences of specific parts. I have been able to get the parts I need into variables while looping through, but I now want to add these to a key with 3 values per file, so a key with 6 values overall which I will then compare to eachother later on. But I can only add 3 values at a time using the loop I have, so I need to be able to add the last 3 values to the key without overwriting the first 3. example of data from file: [\Advanced\Rules\Correlation Rules\Suspect_portscan\]; CheckDescription =S Detect Port scans; Enabled =B 0; Priority =L 3; I have managed to get what I need into variables so I have: string SigName would be "Suspect_portscan" Int Enabled, Priority, Blocking as 0 3 and null respectivly. I then want to make a dictionary type thing, with a key which would be the SigName and the first 3 values as enabled, priority, blocking. Then when looping through the second file, I want to add the 2nd files settings for the enabled, priority, blocking for the same SigName (so to the key) in the last 3 value slots. I will then compare this against itself, like 'if signame(0) != signame(3)' so if file 1 enabled is not the same as file two enabled make a note and tell me. But the problem I have is not being able to get the data into a dictionary or lookup, I'm completely stumped. It seems like I should use a dictionary with a list for the values but I cant get it working on the second loop through. Thanks.

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• C++: defining maximum/minimum limits for a class

  - by Luis

  Basically what the title says... I have created a class that models time slots in a variable-granularity daily schedule (where for example the first time slot is 30 minutes, but the second time slot can be 40 minutes); the first available slot starts at (a value comparable to) 1. What I want to do now is to define somehow the maximum and minimum allowable values that this class takes and I have two practical questions in order to do so: 1.- does it make sense to define absolute minimum and maximum in such a way for a custom class? Or better, does it suffice that a value always compares as lower-than any other possible value of the type, given the class's defined relational operators, to be defined the min? (and analogusly for the max) 2.- assuming the previous question has an answer modeled after "yes" (or "yes but ..."), how do I define such max/min? I know that there is std::numeric_limits<> but from what I read it is intended for "numeric types". Do I interpret that as meaning "represented as a number" or can I make a broader assumption like "represented with numbers" or "having a correspondence to integers"? After all, it would make sense to define the minimum and maximum for a date class, and maybe for a dictionary class, but numeric_limits may not be intended for those uses (I don't have much experience with it). Plus, numeric_limits has a lot of extra members and information that I don't know what to make with. If I don't use numeric_limits, what other well-known / widely-used mechanism does C++ offer to indicate the available range of values for a class?

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• error: expected ',' or '...' before numeric constant

  - by goldfrapp04

  Just a Qt Gui Application with QDialog as the Base Class, the simplest type you can expect. I've programmed on Qt for several times but this is the first time I meet this problem... I've added minimal code to the program, and here's the code in dialog.h (which is mostly automatically generated) #ifndef DIALOG_H #define DIALOG_H #include <QDialog> #include <QPixmap> #include "bmp.h" namespace Ui { class Dialog; } class Dialog : public QDialog { Q_OBJECT public: explicit Dialog(QWidget *parent = 0); ~Dialog(); private slots: void on_openButton_clicked(); private: Ui::Dialog *ui; BMP srcImage; QImage compressedImage[3]; }; #endif // DIALOG_H While I edit, the "public:" is underlined and says "unexpected token '('". When I try to build the program, it says in the line "Q_OBJECT", "error: expected ',' or '...' before numeric constant". I'm sure I've defined nothing related to it (to be exact, I defined an N and an n in file bmp.h, both are int). Any idea of what's wrong here? Thanks.

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• C++ variable to const expression

  - by user1344784

  template <typename Real> class A{ }; template <typename Real> class B{ }; //... a few dozen more similar template classes class Computer{ public slots: void setFrom(int from){ from_ = from; } void setTo(int to){ to_ = to; } private: template <int F, int T> void compute(){ using boost::fusion::vector; using boost::fusion::at_c; vector<A<float>, B<float>, ...> v; at_c<from_>(v).operator()(at_c<to_>(v)); //error; needs to be const-expression. }; This question isn't about Qt, but there is a line of Qt code in my example. The setFrom() and setTo() are functions that are called based on user selection via the GUI widget. The root of my problem is that 'from' and 'to' are variables. In my compute member function I need to pick a type (A, B, etc.) based on the values of 'from' and 'to'. The only way I know how to do what I need to do is to use switch statements, but that's extremely tedious in my case and I would like to avoid. Is there anyway to convert the error line to a constant-expression?

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• pthread_create followed by pthread_detach still results in possibly lost error in Valgrind.

  - by alesplin

  I'm having a problem with Valgrind telling me I have some memory possible lost: ==23205== 544 bytes in 2 blocks are possibly lost in loss record 156 of 265 ==23205== at 0x6022879: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==23205== by 0x540E209: allocate_dtv (in /lib/ld-2.12.1.so) ==23205== by 0x540E91D: _dl_allocate_tls (in /lib/ld-2.12.1.so) ==23205== by 0x623068D: pthread_create@@GLIBC_2.2.5 (in /lib/libpthread-2.12.1.so) ==23205== by 0x758D66: MTPCreateThreadPool (MTP.c:290) ==23205== by 0x405787: main (MServer.c:317) The code that creates these threads (MTPCreateThreadPool) basically gets an index into a block of waiting pthread_t slots, and creates a thread with that. TI becomes a pointer to a struct that has a thread index and a pthread_t. (simplified/sanitized): for (tindex = 0; tindex < NumThreads; tindex++) { int rc; TI = &TP->ThreadInfo[tindex]; TI->ThreadID = tindex; rc = pthread_create(&TI->ThreadHandle,NULL,MTPHandleRequestsLoop,TI); /* check for non-success that I've omitted */ pthread_detach(&TI->ThreadHandle); } Then we have a function MTPDestroyThreadPool that loops through all the threads we created and cancels them (since the MTPHandleRequestsLoop doesn't exit). for (tindex = 0; tindex < NumThreads; tindex++) { pthread_cancel(TP->ThreadInfo[tindex].ThreadHandle); } I've read elsewhere (including other questions here on SO) that detaching a thread explicitly would prevent this possibly lost error, but it clearly isn't. Any thoughts?

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• What is the fastest (to access) struct-like object in Python?

  - by DNS

  I'm optimizing some code whose main bottleneck is running through and accessing a very large list of struct-like objects. Currently I'm using namedtuples, for readability. But some quick benchmarking using 'timeit' shows that this is really the wrong way to go where performance is a factor: Named tuple with a, b, c: >>> timeit("z = a.c", "from __main__ import a") 0.38655471766332994 Class using __slots__, with a, b, c: >>> timeit("z = b.c", "from __main__ import b") 0.14527461047146062 Dictionary with keys a, b, c: >>> timeit("z = c['c']", "from __main__ import c") 0.11588272541098377 Tuple with three values, using a constant key: >>> timeit("z = d[2]", "from __main__ import d") 0.11106188992948773 List with three values, using a constant key: >>> timeit("z = e[2]", "from __main__ import e") 0.086038238242508669 Tuple with three values, using a local key: >>> timeit("z = d[key]", "from __main__ import d, key") 0.11187358437882722 List with three values, using a local key: >>> timeit("z = e[key]", "from __main__ import e, key") 0.088604143037173344 First of all, is there anything about these little timeit tests that would render them invalid? I ran each several times, to make sure no random system event had thrown them off, and the results were almost identical. It would appear that dictionaries offer the best balance between performance and readability, with classes coming in second. This is unfortunate, since, for my purposes, I also need the object to be sequence-like; hence my choice of namedtuple. Lists are substantially faster, but constant keys are unmaintainable; I'd have to create a bunch of index-constants, i.e. KEY_1 = 1, KEY_2 = 2, etc. which is also not ideal. Am I stuck with these choices, or is there an alternative that I've missed?

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• Qtimer not timing out QT, C++

  - by realz

  Hi, I am learning C++ and using QT. I have a small program in which I am trying to update the text of the PushButton every second. The label being current time. I have a timer that should time out every second, but seems like it never does. here's the code. Header File #ifndef _HELLOFORM_H #define _HELLOFORM_H #include "ui_HelloForm.h" class HelloForm : public QDialog { public: HelloForm(); virtual ~HelloForm(); public slots: void textChanged(const QString& text); void updateCaption(); private: Ui::HelloForm widget; }; #endif /* _HELLOFORM_H */ CPP file #include "HelloForm.h" #include <QTimer> #include <QtGui/QPushButton> #include <QTime> HelloForm::HelloForm(){ widget.setupUi(this); widget.pushButton->setText(QTime::currentTime().toString()); widget.pushButton->setFont(QFont( "Times", 9, QFont::Bold ) ); QTimer *timer = new QTimer(this); connect(timer, SIGNAL(timeout()), SLOT(updateCaption())); timer->start(1000); connect(widget.pushButton, SIGNAL(clicked()), qApp, SLOT(quit()) ); connect(widget.nameEdit, SIGNAL(textChanged(const QString&)), this, SLOT(textChanged(const QString&))); } HelloForm::~HelloForm() { } void HelloForm::textChanged(const QString& text) { if (0 < text.trimmed().length()) { widget.helloEdit->setText("Hello " + text.trimmed() + "!"); } else { widget.helloEdit->clear(); } } void HelloForm::updateCaption() { QString myVar; myVar = QTime::currentTime().toString(); widget.pushButton->setText(myVar); } Any help will be greatly appreciated... The PushButton's text never changes...

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• Save the Date - Oracle Partner Community Forum: Exadata, Exalogic and Manageability, Vienna, 23-24 April 2013

  - by Javier Puerta

  Hardware and Software Engineered to Work Together .Ritu { font-family: Arial, Helvetica, sans-serif; } .Ritu { font-family: Arial, Helvetica, sans-serif; } .Ritu { font-family: Arial, Helvetica, sans-serif; } body,td,th { font-family: Arial, Helvetica, sans-serif; font-size: x-small; } .color { color: #F00; } .c { color: #F00; } .c { color: #F00; } .c { color: #000; font-size: xx-small; } .c a { color: #F00; } .c { color: #F00; } .cl { color: #F00; } .b { color: #000; font-size: xx-small; } .i { font-style: italic; } .i { font-style: italic; } .i { font-style: italic; } .i { font-style: italic; } .i { font-style: italic; } .c { color: #F00; font-size: small; } .b { font-weight: bold; font-size: x-small; } .c { color: #F00; font-size: x-small; } .clr { color: #F00; } .c { color: #F00; } inside the Click Here The order you must follow to make the colored link appear in browsers. If not the default window link will appear 1. Select the word you want to use for the link 2. Select the desired color, Red, Black, etc 3. Select bold if necessary ___________________________________________________________________________________________________________________ Templates use two sizes of fonts and the sans-serif font tag for the email. All Fonts should be (Arial, Helvetica, sans-serif) tags Normal size reading body fonts should be set to the size of 2. Small font sizes should be set to 1 !!!!!!!DO NOT USE ANY OTHER SIZE FONT FOR THE EMAILS!!!!!!!! ___________________________________________________________________________________________________________________ -- Oracle PartnerNetwork | Account | Feedback SAVE THE DATE ORACLE PARTNER COMMUNITY FORUM: EXADATA, EXALOGIC AND MANAGEABILITY 23-24 APRIL 2013, VIENNA, AUSTRIA The 2013 event expands its scope to cover all the building blocks of the Cloud infrastructure: Exadata, Exalogic and Manageability! Dear partner I am delighted to announce the 2013 edition of the Exadata, Exalogic and Manageability Partner Community Forum for EMEA partners which will take place in Vienna, Austria, on April 23-24, 2013. After the experience of last year where we ran a joint Exadata and Manageability event, we received requests from many of you to add also Exalogic to the scope of the forum, and this way to cover the complete infrastructure architecture on the Exa platform. The continued market adoption of Exadata and Exalogic is being paralleled by a growth in the rate of projects sold and implemented by partners. Sharing customer cases and best-practices presented by other partners constitutes the core of this event. If you want to present an experience of your company around Exadata, Exalogic or Manageability that can be a learning experience for other partners, we still have some slots in the agenda. (Please contact Javier Puerta if you want to present.) Attending the Community Forum you will also have the opportunity to get Oracle’s insight on new products and market trends. And, of course, interact with the Oracle executives responsible for the Exadata, Exalogic and Manageability business. The atmosphere of beautiful Vienna will be the scenario of the event. Detailed venue and hotel booking information will be sent to you in January. Don't miss out on attending this key event! Save the date now - 23 & 24 April 2013, and watch out for your formal invitation coming soon. Kind regards, Javier Puerta Core Technology Partner Programs, Oracle EMEA E-Mail: [email protected] Jürgen Kress SOA Partner Adoption Oracle EMEA E-Mail: [email protected] Copyright © 2012, Oracle and/or its affiliates. All rights reserved. Contact PBC | Legal Notices and Terms of Use | Privacy Oracle Corporation - Worldwide Headquarters, 500 Oracle Parkway, OPL - E-mail Services, Redwood Shores, CA 94065, United States

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