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• How to create a container that holds different types of function pointers in C++?

  - by Alex

  I'm doing a linear genetic programming project, where programs are bred and evolved by means of natural evolution mechanisms. Their "DNA" is basically a container (I've used arrays and vectors successfully) which contain function pointers to a set of functions available. Now, for simple problems, such as mathematical problems, I could use one type-defined function pointer which could point to functions that all return a double and all take as parameters two doubles. Unfortunately this is not very practical. I need to be able to have a container which can have different sorts of function pointers, say a function pointer to a function which takes no arguments, or a function which takes one argument, or a function which returns something, etc (you get the idea)... Is there any way to do this using any kind of container ? Could I do that using a container which contains polymorphic classes, which in their turn have various kinds of function pointers? I hope someone can direct me towards a solution because redesigning everything I've done so far is going to be painful.

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• Passing big multi-dimensional array to function in C

  - by kirbuchi

  Hi, I'm having trouble passing a big array to a function in C. I declare: int image[height][width][3]={}; where height and width can be as big as 1500. And when I call: foo((void *)image,height,width); which is declared as follows: int *foo(const int *inputImage, int h, int w); I get segmentation fault error. What's strange is that if my values are: height=1200; width=290; theres no problem, but when they're: height=1200; width=291; i get the mentioned error. At 4 bytes per integer with both height and width of 1500 (absolute worst case) the array size would be of 27MB which imo isn't that big and shouldn't really matter because I'm only passing a pointer to the first element of the array. Any advice?

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• Storing member function pointers of derived classes in map

  - by Kiran Mohan

  Hello, I am trying to implement a factory for two classes Circle, Square both of which inherits from Shape. class Shape { public: virtual static Shape * getInstance() = 0; }; class Circle : public Shape { public: static const std::string type; Shape * getInstance() { return new Circle; } }; const std::string Circle::type = "Circle"; class Square : public Shape { public: static const std::string type; Shape * getInstance() { return new Square; } }; const std::string Square::type = "Square"; I want to now create a map with key as shape type (string) and value as a function pointer to getInstance() of the corresponding derived class. Is it possible? Thanks, Kiran

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• Timing Calculations for Opengl ES 2.0 draw calls

  - by Arun AC

  I am drawing a cube in OpenGL ES 2.0 in Linux. I am calculating the time taken for each frame using below function #define NANO 1000000000 #define NANO_TO_MICRO(x) ((x)/1000) uint64_t getTick() { struct timespec stCT; clock_gettime(CLOCK_MONOTONIC, &stCT); uint64_t iCurrTimeNano = (1000000000 * stCT.tv_sec + stCT.tv_nsec); // in Nano Secs uint64_t iCurrTimeMicro = NANO_TO_MICRO(iCurrTimeNano); // in Micro Secs return iCurrTimeMicro; } I am running my code for 100 frames with simple x-axis rotation. I am getting around 200 to 220 microsecs per frame. that means am i getting around (1/220microsec = 4545) FPS Is my GPU is that fast? I strongly doubt this result. what went wrong in the code? Regards, Arun AC

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• Using typedefs from a template class in a template (non-member) function

  - by atomicpirate

  The following fails to compile (with gcc 4.2.1 on Linux, anyway): template< typename T > class Foo { public: typedef int FooType; }; void ordinary() { Foo< int >::FooType bar = 0; } template< typename T > void templated() { Foo< T >::FooType bar = T( 0 ); } int main( int argc, char **argv ) { return 0; } The problem is with this line: Foo< T >::FooType bar = 0; ...and the compiler makes this complaint: foo.c: In function ‘void templated()’: foo.c:22: error: expected `;' before ‘bar’ Normally one sees this when a type hasn't been declared, but as far as I can tell, Foo< T ::FooType should be perfectly valid inside templated().

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• SQL Split function.

  - by Wardy

  Hi guys, I'm looking for a way to do this ... SELECT FirstName, LastName, Split(AddressBlock, ' ', 1), Split(AddressBlock, ' ', 2), PostCode FROM Contacts The arguments I want to pass are ... The address The separator (current situation requires 2 spaces but this might be a comma or a space followed by a comma) or something else (it varies). The address part I want to return (i don't always need all parts of the split result). I seem to be able to find a few examples of splitting functions about the internet but they return a table containing the entire set of split parts. My SQL skills aren't that great so I need the answer to be ultra simple. I'm always working with nvarchar data and the function needs to be reusable.

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• Select from table and function

  - by David Oneill

  I have a function that returns a table. The returned table contains (among other things) a store_id. I can get the store_id for a particular transaction_id and city_id as follows: select store_id from table(f_get_store(city_id, transaction_id)); I have another table that contains a list of transactions (which includes transaction_id and city_id). I want a query that returns store_id, city_id, transaction_id for every entry in the transaction table. My first guess was: select f_get_store(city_id, transaction_id), city_id, transaction_id from table; (simplified away the unimportant details) However, this yields an "ORA-00932: inconsistent datatypes" error. How do I need to structure this query? (I'm using Oracle)

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• android call an outside function from a thread

  - by junmats

  hi.. say for example I have this code in my activity: public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Thread cThread = new Thread(new Runner()); cThread.start(); } private NotifyMe(){ //do something here } and this is my Runner class: public class TCPClient implements Runnable { public void run(){ //call NotifyMe() [THIS IS MY QUESTION] } } I have a thread on my activity that runs the Runner Class. Once the thread start, I would like to call the NotifyMe() function that is located at the activity. Is this possible? Please let me know if you don't understand my question. Thanks in advance.

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• Invalid conversion from int to int** C++

  - by user69514

  Not sure why I'm getting this error. I have the following: int* arr = new int[25]; int* foo(){ int* i; cout << "Enter an integer:"; cin >> *i; return i; } void test(int** myInt){ *myInt = foo(); } This call here is where I get the error: test(arr[0]); //here i get invalid conversion from int to int**

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• Using php's magic function inside another function does not work

  - by Sirber

  I want to use magic function __set() and __get() for storing SQL data inside a php5 class and I get some strange issue using them inside a function: Works: if (!isset($this->sPrimaryKey) || !isset($this->sTable)) return false; $id = $this->{$this->sPrimaryKey}; if (empty($id)) return false; echo 'yaay!'; Does not work: if (!isset($this->sPrimaryKey) || !isset($this->sTable)) return false; if (empty($this->{$this->sPrimaryKey})) return false; echo 'yaay!'; would this be a php bug?

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• Calling home, receiving calls and smartphone data from the US

  - by Rob Farley

  I got asked about calling home from the US, by someone going to the PASS Summit. I found myself thinking “there should be a blog post about this”... The easiest way to phone home is Skype - no question. Use WiFi, and if you’re calling someone who has Skype on their phone at the other end, it’s free. Even if they don’t, it’s still pretty good price-wise. The PASS Summit conference centre has good WiFI, as do the hotels, and plenty of other places (like Starbucks). But if you’re used to having data all the time, particularly when you’re walking from one place to another, then you’ll want a sim card. This also lets you receive calls more easily, not just solving your data problem. You’ll need to make sure your phone isn’t locked to your local network – get that sorted before you leave. It’s no trouble to drop by a T-mobile or AT&T store and getting a prepaid sim. You can’t get one from the airport, but if the PASS Summit is your first stop, there’s a T-mobile store on 6th in Seattle between Pine & Pike, so you can see it from the Sheraton hotel if that’s where you’re staying. AT&T isn’t far away either. But – there’s an extra step that you should be aware of. If you talk to one of these US telcos, you’ll probably (hopefully I’m wrong, but this is how it was for me recently) be told that their prepaid sims don’t work in smartphones. And they’re right – the APN gets detected and stops the data from working. But luckily, Apple (and others) have provided information about how to change the APN, which has been used by a company based in New Zealand to let you get your phone working. Basically, you send your phone browser to http://unlockit.co.nz and follow the prompts. But do this from a WiFi place somewhere, because you won’t have data access until after you’ve sorted this out... Oh, and if you get a prepaid sim with “unlimited data”, you will still need to get a Data Feature for it. And just for the record – this is WAY easier if you’re going to the UK. I dropped into a T-mobile shop there, and bought a prepaid sim card for five quid, which gave me 250MB data and some (but not much) call credit. In Australia it’s even easier, because you can buy data-enabled sim cards that work in smartphones from the airport when you arrive. I think having access to data really helps you feel at home in a different place. It means you can pull up maps, see what your friends are doing, and more. Hopefully this post helps, but feel free to post comments with extra information if you have it. @rob_farley

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• Haskell IO Passes to Another Function

  - by peterwkc

  This question here is related to http://stackoverflow.com/questions/3066956/haskell-input-return-tuple I wonder how we can passes the input from monad IO to another function in order to do some computation. Actually what i want is something like -- First Example test = savefile investinput -- Second Example maxinvest :: a maxinvest = liftM maximuminvest maxinvestinput maxinvestinput :: IO() maxinvestinput = do str <- readFile "C:\\Invest.txt" let cont = words str let mytuple = converttuple cont let myint = getint mytuple putStrLn "" -- Convert to Tuple converttuple :: [String] -> [(String, Integer)] converttuple [] = [] converttuple (x:y:z) = (x, read y):converttuple z -- Get Integer getint :: [(String, Integer)] -> [Integer] getint [] = [] getint (x:xs) = snd (x) : getint xs -- Search Maximum Invest maximuminvest :: (Ord a) => [a] -> a maximuminvest [] = error "Empty Invest Amount List" maximuminvest [x] = x maximuminvest (x:xs) | x > maxTail = x | otherwise = maxTail where maxTail = maximuminvest xs In the second example, the maxinvestinput is read from file and convert the data to the type maximuminvest expected. Please help. Thanks.

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• Passing a 2D array to a function in C

  - by Tyler Treat

  I have, essentially, a matrix of data (lets say ints) that I would like to store in a 2D array in which the dimensions are not known until runtime (say x columns and y rows). I want to populate the array in a function, so I assume I need to do something like this: int main(int argc, char **argv) { int y = atoi(argv[1]); int x = atoi(argv[2]); int **matrix = malloc(x * sizeof(int*)); populateMatrix(matrix, y, x); return 0; } void populateMatrix(**matrix, int y, int x) { int i, j; for (i = 0; i < y; i++) { for (j = 0; j < x; j++) { matrix[i][j] = i * j; // populated with trivial data to keep it simple } } } Obviously this doesn't work, but I'm not sure how to do what I'm describing exactly.

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• Javascript function as a parameter to another function?

  - by Alex

  Hello there, I'm learning lots of javascript these days, and one of the things I'm not quite understanding is passing functions as parameters to other functions. I get the concept of doing such things, but I myself can't come up with any situations where this would be ideal? My question is: When do you want to have your javascript functions take another function as a parameter? Why not just assign a variable to that functions return value and pass that variable to the function like so: // Why not do this var foo = doStuff(params); callerFunction(foo); //instead of this callerFunction(doStuff); I'm confused as to why I would ever choose to do things as in my second example. Why would you do this? What are the use cases? Thanks!!

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• Returning a local object from a function

  - by pocoa

  Is this the right way to return an object from a function? Car getCar(string model, int year) { Car c(model, year); return c; } void displayCar(Car &car) { cout << car.getModel() << ", " << car.getYear() << endl; } displayCar(getCar("Honda", 1999)); I'm getting an error, "taking address of temporary". Should I use this way: Car &getCar(string model, int year) { Car c(model, year); return c; }

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• template class: ctor against function -> new C++ standard

  - by Oops

  Hi in this question: http://stackoverflow.com/questions/2779155/template-point2-double-point3-double Dennis and Michael noticed the unreasonable foolishly implemented constructor. They were right, I didn't consider this at that moment. But I found out that a constructor does not help very much for a template class like this one, instead a function is here much more convenient and safe namespace point { template < unsigned int dims, typename T > struct Point { T X[ dims ]; std::string str() { std::stringstream s; s << "{"; for ( int i = 0; i < dims; ++i ) { s << " X" << i << ": " << X[ i ] << (( i < dims -1 )? " |": " "); } s << "}"; return s.str(); } Point<dims, int> toint() { Point<dims, int> ret; std::copy( X, X+dims, ret.X ); return ret; } }; template < typename T > Point< 2, T > Create( T X0, T X1 ) { Point< 2, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; return ret; } template < typename T > Point< 3, T > Create( T X0, T X1, T X2 ) { Point< 3, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; ret.X[ 2 ] = X2; return ret; } template < typename T > Point< 4, T > Create( T X0, T X1, T X2, T X3 ) { Point< 4, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; ret.X[ 2 ] = X2; ret.X[ 3 ] = X3; return ret; } }; int main( void ) { using namespace point; Point< 2, double > p2d = point::Create( 12.3, 34.5 ); Point< 3, double > p3d = point::Create( 12.3, 34.5, 56.7 ); Point< 4, double > p4d = point::Create( 12.3, 34.5, 56.7, 78.9 ); //Point< 3, double > p1d = point::Create( 12.3, 34.5 ); //no suitable user defined conversion exists //Point< 3, int > p1i = p4d.toint(); //no suitable user defined conversion exists Point< 2, int > p2i = p2d.toint(); Point< 3, int > p3i = p3d.toint(); Point< 4, int > p4i = p4d.toint(); std::cout << p2d.str() << std::endl; std::cout << p3d.str() << std::endl; std::cout << p4d.str() << std::endl; std::cout << p2i.str() << std::endl; std::cout << p3i.str() << std::endl; std::cout << p4i.str() << std::endl; char c; std::cin >> c; } has the new C++ standard any new improvements, language features or simplifications regarding this aspect of ctor of a template class? what do you think about the implementation of the combination of namespace, stuct and Create function? many thanks in advance Oops

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• How to do an if statement on a function in PHP?

  - by Bruce

  I just realized that you can't just use an if statement on a function, for example this doesn't work: function sayHello() { echo "Hello World"; } if(sayHello()) echo "Function Worked"; else echo "Function Failed"; I also saw that a function can't be put as the value of a variable. So how can I do an if statement to check if a function has executed properly and display it to the browser?

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• Template meta-programming with member function pointers?

  - by wheaties

  Is it possible to use member function pointers with template meta-programming? Such as: class Connection{ public: string getName() const; string getAlias() const; //more stuff }; typedef string (Connection::*Con_Func)() const; template<Con_Func _Name> class Foo{ Connection m_Connect; public: void Foo(){ cout << m_Connect.(*_Name); } }; typedef Foo<&Connection::getName> NamedFoo; typedef Foo<&Connection::getAlias> AliasFoo; Granted, this is rather contrived but is it possible? (yes, there are probably much better ways but humor me.)

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• Const Member function Vs Const Friend Function

  - by strut

  How this code modifies a value in a const function: http://www.ideone.com/vjVsf And this code gives an error: http://www.ideone.com/346Xg

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• "Inline" function call: function is never hit

  - by Shimrod

  Hi everybody. I'm trying to make a tabbed menu for the asp.net website I'm working on. One of the pre-requisite is obviously to color the current tab differently, so the user can know on which tab is currently is. To do this, I made this method in my code-behind: Protected Function GetCssClass(ByVal ctrl As LinkButton) As String If ctrl.ID = currentLink Then Return "current" Else Return String.Empty End If End Function and I call the method like this in my aspx page: <asp:LinkButton ID="LinkButton1" runat="server" PostBackUrl="/Default.aspx" CssClass="<%#GetCssClass(LinkButton1) %>" >Home</asp:LinkButton> <asp:LinkButton ID="LinkButton2" runat="server" PostBackUrl="/Directory/page1.aspx" CssClass="<%#GetCssClass(LinkButton2) %>" >Page1</asp:LinkButton> But the method is never hit... As I understand, the method should be called each time the LinkButton is drawn... Does someone have an idea why? Thanks in advance !

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• Creating a function that will handle objects with common properties

  - by geocine

  Take this as an example I have trimmed this example for readability and you may not find the use of this concept here. class Teacher() { public Name {get; set;} public Salt {get; set;} public Department{get; set;} } class Student() { public Name {get; set;} public Salt {get; set;} public Section{get; set;} } public string GetEncryptedName(object Person) { //return encrypted name based on Name and Salt property return encrypt(object.Salt,object.Name) } callig the function GetEncryptedName(Teacher) GetEncryptedName(Student) How do you implement this kind of stuff?

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• Possible to change function name in definition?

  - by Bird Jaguar IV

  I tried several ways to change the function name in the definition, but they failed. >>> def f(): pass >>> f.__name__ 'f' >>> def f(): f.__name__ = 'new name' >>> f.__name__ 'f' >>> def f(): self.__name__ = 'new name' >>> f.__name__ 'f' But I can change the name attribute after defining it. >>> def f(): pass >>> f.__name__ = 'new name' >>> f.__name__ 'new name' Any way to change/set it in the definition (other than using a decorator)?

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• Function declaration in C and C++

  - by Happy Mittal

  I have two C++ files, say file1.cpp and file2.cpp as //file1.cpp #include<cstdio> void fun(int i) { printf("%d\n",i); } //file2.cpp void fun(double); int main() { fun(5); } When I compile them and link them as c++ files, I get an error "undefined reference to fun(double)". But when I do this as C files, I don't get error and 0 is printed instead of 5. Please explain the reason. Moreover I want to ask whether we need to declare a function before defining it because I haven't declared it in file1.cpp but no error comes in compilation.

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• Member Function Pointer not quite right

  - by BlackDuck

  I have a SpecialisedRedBlackTree class that is templated. My Month class is not. In my Month class I have a private member which is an instance of SpecialisedRedBlackTree: SpecialisedRedBlackTree<Day> m_windSpeedTree; As you can see it will take the Day class/object (please correct me on any terms I get wrong). In my Month class, I have a method passing a method function pointer to this method: bool Month::CompareWindSpeed(Day a, Day b) { return ( a.GetData(WIND_SPEED_CODE) < b.GetData(WIND_SPEED_CODE)? true : false); } bool (Month::*myFuncPtr)(Day, Day); myFuncPtr = &Month::CompareWindSpeed; m_windSpeedTree.Insert(dayReading, myFuncPtr); But because I am passing a bool (Day, Day) pointer to a templated class expecting bool (T, T) T being part of this .... template Error 1 error C2664: 'SpecialisedRedBlackTree<T>::Insert' : cannot convert parameter 2 from 'bool (__thiscall Month::* )(Day,Day)' to 'bool (__cdecl *)(T,T)' Any advice?

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• Android Camera takePicture function does not call Callback function

  - by Tomáš 'Guns Blazing' Frcek

  I am working on a custom Camera activity for my application. I was following the instruction from the Android Developers site here: http://developer.android.com/guide/topics/media/camera.html Everything seems to works fine, except the Callback function is not called and the picture is not saved. Here is my code: public class CameraActivity extends Activity { private Camera mCamera; private CameraPreview mPreview; private static final String TAG = "CameraActivity"; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.camera); // Create an instance of Camera mCamera = getCameraInstance(); // Create our Preview view and set it as the content of our activity. mPreview = new CameraPreview(this, mCamera); FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview); preview.addView(mPreview); Button captureButton = (Button) findViewById(R.id.button_capture); captureButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Log.v(TAG, "will now take picture"); mCamera.takePicture(null, null, mPicture); Log.v(TAG, "will now release camera"); mCamera.release(); Log.v(TAG, "will now call finish()"); finish(); } }); } private PictureCallback mPicture = new PictureCallback() { @Override public void onPictureTaken(byte[] data, Camera camera) { Log.v(TAG, "Getting output media file"); File pictureFile = getOutputMediaFile(); if (pictureFile == null) { Log.v(TAG, "Error creating output file"); return; } try { FileOutputStream fos = new FileOutputStream(pictureFile); fos.write(data); fos.close(); } catch (FileNotFoundException e) { Log.v(TAG, e.getMessage()); } catch (IOException e) { Log.v(TAG, e.getMessage()); } } }; private static File getOutputMediaFile() { String state = Environment.getExternalStorageState(); if (!state.equals(Environment.MEDIA_MOUNTED)) { return null; } else { File folder_gui = new File(Environment.getExternalStorageDirectory() + File.separator + "GUI"); if (!folder_gui.exists()) { Log.v(TAG, "Creating folder: " + folder_gui.getAbsolutePath()); folder_gui.mkdirs(); } File outFile = new File(folder_gui, "temp.jpg"); Log.v(TAG, "Returnng file: " + outFile.getAbsolutePath()); return outFile; } } After clicking the Button, I get logs: "will now take picture", "will now release camera" and "will now call finish". The activity finishes succesfully, but the Callback function was not called during the mCamera.takePicture(null, null, mPicture); function (There were no logs from the mPicture callback or getMediaOutputFile functions) and there is no file in the location that was specified. Any ideas? :) Much thanks!

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