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  • How do you return a pointer to a base class with a virtual function?

    - by Nick Sweet
    I have a base class called Element, a derived class called Vector, and I'm trying to redefine two virtual functions from Element in Vector. //element.h template <class T> class Element { public: Element(); virtual Element& plus(const Element&); virtual Element& minus(const Element&); }; and in another file //Vector.h #include "Element.h" template <class T> class Vector: public Element<T> { T x, y, z; public: //constructors Vector(); Vector(const T& x, const T& y = 0, const T& z =0); Vector(const Vector& u); ... //operations Element<T>& plus(const Element<T>& v) const; Element<T>& minus(const Element<T>& v) const; ... }; //sum template <class T> Element<T>& Vector<T>::plus(const Element<T>& v) const { Element<T>* ret = new Vector((x + v.x), (y + v.y), (z + v.z)); return *ret; } //difference template <class T> Element<T>& Vector<T>::minus(const Element<T>& v) const { Vector<T>* ret = new Vector((x - v.x), (y - v.y), (z - v.z)); return *ret; } but I always get error: 'const class Element' has no member named 'getx' So, can I define my virtual functions to take Vector& as an argument instead, or is there a way for me to access the data members of Vector through a pointer to Element? I'm still fairly new to inheritance polymorphism, fyi.

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  • Why should GoTos be bad?

    - by lisn
    I'm using gotos and a lot of them. C++, PHP or COBOL - I use them on nearly all occasions where everybody else would use functions or even classes. Yet my code is Clear Maintainable Bug-free Fast So why does everybody I meet tell me about how bad gotos are? Are there any facts that show that they are "bad"?

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  • color objects in C or C ++ [closed]

    - by jazz
    Possible Duplicate: Colors in C language i copied a game from a book which name is paratrooper i ask this question again i also provide the code of the objects which i create there i want to change the color of these objects but i didn't understand how to do that so can any one plz help me how to do that.Listen guys they are not the standard functions but i use the graphics library for these functions and i can't find the function in the library file of graphics. i hope u understand know.this code will not run properly so plz tell me something about the function which color it i can't put the image other wize i show u the image it will make alot easieer #include "graphics.h" #include "stdio.h" #include "conio.h" #include "process.h" #include "alloc.h" #include "stdlib.h" #include "math.h" #include "dos.h" main() { int gm=CGAHI, gd=CGA, key=0, area; initgraph(&gd, &gm, "C:\\tc\\bgi"); helidraw(246,50,-1); getch(); return 0; } helidraw ( int x, int y, int d ) { int direction, i, j ; if ( d ) direction = -1 ; else direction = 1 ; i = 3 ; j = 8 ; line ( x - j - 8, y - i - 2, x + j + 8, y - i - 2 ) ; line ( x - j + 5, y - i - 1, x + j - 5, y - i - 1 ) ; line ( x - j, y - i, x + j, y - i ) ; for ( ; i > 0 ; i--, j += 2 ) { putpixel ( x - ( direction * j ), y - i, 1 ) ; line ( x + ( direction * j ), y - i, x + ( direction * ( j - 8 ) ), y - i ) ; } i = 0 ; j -= 2 ; line ( x - ( direction * j ), y - i, x - ( direction * ( j + 17 ) ), y - i ) ; line ( x - ( direction * j ), y - i + 1, x - ( direction * ( j + 7 ) ), y - i + 1 ) ; putpixel ( x - ( direction * ( j + 19 ) ), y - i - 1, 1 ) ; for ( ; i < 3 ; i++, j -= 2 ) { putpixel ( x - j, y + i, 1 ) ; putpixel ( x + j, y + i, 1 ) ; } line ( x - j, y + i, x + j, y + i ) ; putpixel ( x - j + 3, y + i + 1, 1 ) ; putpixel ( x + j - 3, y + i + 1, 1 ) ; line ( x - j - 10, y + i + 2, x + j + 10, y + i + 2 ) ; putpixel ( x + ( direction * ( j + 12 ) ), y + i + 1, 1 ) ; }

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  • C#: My callback function gets called twice for every Sent Request

    - by Madi D.
    I've Got a program that uploads/downloads files into an online server,Has a callback to report progress and log it into a textfile, The program is built with the following structure: public void Upload(string source, string destination) { //Object containing Source and destination to pass to the threaded function KeyValuePair<string, string> file = new KeyValuePair<string, string>(source, destination); //Threading to make sure no blocking happens after calling upload Function Thread t = new Thread(new ParameterizedThreadStart(amazonHandler.TUpload)); t.Start(file); } private void TUpload(object fileInfo) { KeyValuePair<string, string> file = (KeyValuePair<string, string>)fileInfo; /* Some Magic goes here,Checking The file and Authorizing Upload */ var ftiObject = new FtiObject () { FileNameOnHDD = file.Key, DestinationPath = file.Value, //Has more data used for calculations. }; //Threading to make sure progress gets callback gets called. Thread t = new Thread(new ParameterizedThreadStart(amazonHandler.UploadOP)); t.Start(ftiObject); //Signal used to stop progress untill uploadCompleted is called. uploadChunkDoneSignal.WaitOne(); /* Some Extra Code */ } private void UploadOP(object ftiSentObject) { FtiObject ftiObject = (FtiObject)ftiSentObject; /* Some useless code to create the uri and prepare the ftiObject. */ // webClient.UploadFileAsync will open a thread that // will upload the file and report // progress/complete using registered callback functions. webClient.UploadFileAsync(uri, "PUT", ftiObject.FileNameOnHDD, ftiObject); } I got a callback that is registered to the Webclient's UploadProgressChanged event , however it is getting called twice per sent request. void UploadProgressCallback(object sender, UploadProgressChangedEventArgs e) { FtiObject ftiObject = (FtiObject )e.UserState; Logger.log(ftiObject.FileNameOnHDD, (double)e.BytesSent ,e.TotalBytesToSend); } Log Output: Filename: C:\Text1.txt Uploaded:1024 TotalFileSize: 665241 Filename: C:\Text1.txt Uploaded:1024 TotalFileSize: 665241 Filename: C:\Text1.txt Uploaded:2048 TotalFileSize: 665241 Filename: C:\Text1.txt Uploaded:2048 TotalFileSize: 665241 Filename: C:\Text1.txt Uploaded:3072 TotalFileSize: 665241 Filename: C:\Text1.txt Uploaded:3072 TotalFileSize: 665241 Etc... I am watching the Network Traffic using a watcher, and only 1 request is being sent. Some how i cant Figure out why the callback is being called twice, my doubt was that the callback is getting fired by each thread opened(the main Upload , and TUpload), however i dont know how to test if thats the cause. Note: The reason behind the many /**/ Comments is to indicate that the functions do more than just opening threads, and threading is being used to make sure no blocking occurs (there a couple of "Signal.WaitOne()" around the code for synchronization)

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  • Mod_rewrite and redirects with training forward slash not working

    - by john williams
    I'm using the following lines of code in my .htaccess file to create redirects. The problem is, whenever I go to example.com/register/ it cant find the css files because it's looking for example.com/register/mycss.css instead of example.com/mycss.css. Redirect 301 register.php http://example.com/register RewriteRule ^register/?$ register.php How can I correct this? I'm new to any kind of htaccess/mod_rewrite functions so feel free to point me in the right direction if there are any other flaws.

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  • Numpy: Creating a complex array from 2 real ones?

    - by Duncan Tait
    I swear this should be so easy... Why is it not? :( In fact, I want to combine 2 parts of the same array to make a complex array: Data[:,:,:,0] , Data[:,:,:,1] These don't work: x = np.complex(Data[:,:,:,0], Data[:,:,:,1]) x = complex(Data[:,:,:,0], Data[:,:,:,1]) Am I missing something? Does numpy not like performing array functions on complex numbers? Here's the error: TypeError: only length-1 arrays can be converted to Python scalars Cheers

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  • Does this incorporate JavaScript closures?

    - by alex
    In trying to learn JavaScript closures, I've confused myself a bit. From what I've gathered over the web, a closure is... Declaring a function within another function, and that inner function has access to its parent function's variables, even after that parent function has returned. Here is a small sample of script from a recent project. It allows text in a div to be scrolled up and down by buttons. var pageScroll = (function() { var $page, $next, $prev, canScroll = true, textHeight, scrollHeight; var init = function() { $page = $('#secondary-page'); // reset text $page.scrollTop(0); textHeight = $page.outerHeight(); scrollHeight = $page.attr('scrollHeight'); if (textHeight === scrollHeight) { // not enough text to scroll return false; }; $page.after('<div id="page-controls"><button id="page-prev">prev</button><button id="page-next">next</button></div>'); $next = $('#page-next'); $prev = $('#page-prev'); $prev.hide(); $next.click(scrollDown); $prev.click(scrollUp); }; var scrollDown = function() { if ( ! canScroll) return; canScroll = false; var scrollTop = $page.scrollTop(); $prev.fadeIn(500); if (scrollTop == textHeight) { // can we scroll any lower? $next.fadeOut(500); } $page.animate({ scrollTop: '+=' + textHeight + 'px'}, 500, function() { canScroll = true; }); }; var scrollUp = function() { $next.fadeIn(500); $prev.fadeOut(500); $page.animate({ scrollTop: 0}, 500); }; $(document).ready(init); }()); Does this example use closures? I know it has functions within functions, but is there a case where the outer variables being preserved is being used? Am I using them without knowing it? Thanks Update Would this make a closure if I placed this beneath the $(document).ready(init); statement? return { scrollDown: scrollDown }; Could it then be, if I wanted to make the text scroll down from anywhere else in JavaScript, I could do pageScroll.scrollDown(); I'm going to have a play around on http://www.jsbin.com and report back

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  • Experiences with IKVM.NET

    - by Kottan
    Is IKVM.NET a good way to use Java Code or Java Libs in .NET applications ? Has anybody experiences with this tool ? Are there alternatives ? Are there possibilities to call Java functions / code in COM-based applications like Visual Basic 6 or Classical ASP ?

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  • Is there a full REPL for Erlang?

    - by Gabriel Cuvillier
    Is there a way to have a full interpreter in Erlang, not just a "shell". Since it is a dynamic language, not being able to define named functions in the interpreter is a little bit disappointing... I suspect that it is because compilation units (modules) must be explicitly compiled for their execution by the VM, but maybe a REPL acting as a dynamic/recompilable module exist?

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  • What is a de-compiler how does it work?

    - by thyrgle
    So is a decompiler really a thing that gives gives the source of a compiled/interpreted piece of code? Because to me that sounds impossible. How would you get the names of the functions, variables, classes, etc if it is compiled. Or am I misinterpreting the definition? How does it work? And what is the general principal behind making one?

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  • Why are enums considered compound types?

    - by FredOverflow
    Arrays, functions, pointers, references, classes, unions, enumerations and pointers to members are compound types. My understanding of a compound type is that is based on other type(s). For example, T[n], T* and T& are all based on T. Then what other type(s) is an enumeration based on? Or if my understanding of compound types is incorrect, what exactly is it about a type that makes it a compound type? Is compound simply a synonym for user-defined?

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  • Big, Thick Reference Books (PHP / MySQL / Unix) [closed]

    - by Josh K
    I'm looking for in-depth reference books / guides in PHP, MySQL, and Unix. I'm aware there other other questions pertaining to good books for short references of function names, or detailed beginner guides to these systems. I'm looking for something different. I want a book that I can either use as a quick but in-depth (decent write up, not a pocket reference guide) reference to common functions (JOINS, string manipulation, Regular Expressions, etc) while also providing a detailed inner workings explanation on the system itself.

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  • How to Convert Boolean to String

    - by tag
    I have a boolean variable which I want to convert to a string $res = true; I need it the converted value to also be in the format "true" "false" not "0" "1" $converted_res = "true"; $converted_res = "false"; I've tried: $converted_res = string($res); $converted_res = String($res); but it tells me string and String are not recognized functions. How do I convert this boolean to a string in the format "true" or "false" in php?

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  • 3D plotting in Matlab

    - by Jill
    I'm using the subplot and then surf functions to generate images in 3D in Matlab. How do I get rid of the axes and axis' gridlines and change the color to all yellow or all green or something like that? Thanks.

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  • a class function with if(this==NULL) test got compiled?

    - by James
    I saw this code snippet during our lab and it actually compiles in MSVC2008 and G++. void LinkList< class T ::Insert(T n) { if (this == NULL) // some code here } As far as I know the this must not be null since you cannot call a class functions in c++ if it wasn't instantiated. Is this a valid code? if so what's the reason behind and where it can be useful?

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  • Need to have testing server work with https: but don't have an SSL

    - by Cyrcle
    I'm working on an online store. I have it setup on my testing server. I'm having a problem where when it goes to the checkout functions it wants to start calling https pages. I don't have an SSL certificate for this server. Is there something I can do with Apache to get this to work? Mod_Rewrite perhaps? I've played a little with rewrites but haven't had any success.

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  • mysql_query -- question about results "location"

    - by Andrew Heath
    Forgive me if this is a particularly stupid question! mysql_query($query) returns a boolean, but you can also assign it to a variable $results = mysql_query($query) and then use the other mysql_ functions to extract data. Out of curiosity, how does mysq_query($query) act as both a boolean and a data container at the same time? What's happening "under the hood" during these steps? (yes, I am a n00b..., please be kind!)

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  • In flex how do I pass data retrieved from a remote object service to a modules interface?

    - by Dan G
    I found at this Adobe tutorial a nice "RemoteService" class that creates a RemoteObject and contains the functions for handling the result and fault events. If I wanted to use this approach, how could I pass the data from the result handler to interfaces that modules from the main application could use? I could put the RemoteService/RemoteObject in the modules, but (in my opinion- and I could be wrong) the best design seems to be using the remote calls in the main app and passing the data along to the modules.

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  • R: Plotting a graph with different colors of points based on advanced criteria

    - by balconydoor
    What I would like to do is a plot (using ggplot), where the x axis represent years which have a different colour for the last three years in the plot than the rest. The last three years should also meet a certain criteria and based on this the last three years can either be red or green. The criteria is that the mean of the last three years should be less (making it green) or more (making it red) than the 66%-percentile of the remaining years. So far I have made two different functions calculating the last three year mean: LYM3 <- function (x) { LYM3 <- tail(x,3) mean(LYM3$Data,na.rm=T) } And the 66%-percentile for the remaining: perc66 <- function(x) { percentile <- head(x,-3) quantile(percentile$Data, .66, names=F,na.rm=T) } Here are two sets of data that can be used in the calculations (plots), the first which is an example from my real data where LYM3(df1) < perc66(df1) and the second is just made up data where LYM3 perc66. df1<- data.frame(Year=c(1979:2010), Data=c(347261.87, 145071.29, 110181.93, 183016.71, 210995.67, 205207.33, 103291.78, 247182.10, 152894.45, 170771.50, 206534.55, 287770.86, 223832.43, 297542.86, 267343.54, 475485.47, 224575.08, 147607.81, 171732.38, 126818.10, 165801.08, 136921.58, 136947.63, 83428.05, 144295.87, 68566.23, 59943.05, 49909.08, 52149.11, 117627.75, 132127.79, 130463.80)) df2 <- data.frame(Year=c(1979:2010), Data=c(sample(50,29,replace=T),75,75,75)) Here’s my code for my plot so far: plot <- ggplot(df1, aes(x=Year, y=Data)) + theme_bw() + geom_point(size=3, aes(colour=ifelse(df1$Year<2008, "black",ifelse(LYM3(df1) < perc66(df1),"green","red")))) + geom_line() + scale_x_continuous(breaks=c(1980,1985,1990,1995,2000,2005,2010), limits=c(1978,2011)) plot As you notice it doesn’t really do what I want it to do. The only thing it does seem to do is that it turns the years before 2008 into one level and those after into another one and base the point colour off these two levels. Since I don’t want this year to be stationary either, I made another tiny function: fun3 <- function(x) { df <- subset(x, Year==(max(Year)-2)) df$Year } So the previous code would have the same effect as: geom_point(size=3, aes(colour=ifelse(df1$Year<fun3(df1), "black","red"))) But it still does not care about my colours. Why does it make the years into levels? And how come an ifelse function doesn’t work within another one in this case? How would it be possible to the arguments to do what I like? I realise this might be a bit messy, asking for a lot at the same time, but I hope my description is pretty clear. It would be helpful if someone could at least point me in the right direction. I tried to put the code for the plot into a function as well so I wouldn’t have to change the data frame at all functions within the plot, but I can’t get it to work. Thank you!

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  • Prototype's update not working with IE

    - by xain
    Hi, I'm having problems updating a div's content in IE using .update; I also tried with innerHTML with no success. My script works fine with firefox and chrome, but I need to make it work with IE too (neither 7 nor 8 accept the functions). Any hints ? Thanks in advance.

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  • How do you avoid an invalid search space in a genetic algorithm?

    - by Dave
    I am developing a GA for a school project and I've noticed that upon evaluating my functions for fitness, an individual is equivalent to its inverse. For example, the set (1, 1, -1, 1) is equivalent to (-1, -1, 1, -1). To shrink my search space and reach a solution more efficiently, how can I avoid my crossovers from searching in this second half of the search space?

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  • [CakePHP] I am so confused. What should I write in the default.ctp

    - by kwokwai
    Hi all, I am learning cakePHP, everything seems alright except that I am very confused of how to make use of the default.ctp and what should be put inside the Elements folder. Here is the default.ctp file that I have been using since my very first lesson on learning cakePHP: (I copied from this URL http://book.cakephp.org/view/96/Layouts) <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title><?php echo $title_for_layout?></title> <link rel="shortcut icon" href="favicon.ico" type="image/x-icon"> <!-- Include external files and scripts here (See HTML helper for more info.) --> <?php echo $scripts_for_layout ?> </head> <body> <!-- If you'd like some sort of menu to show up on all of your views, include it here --> <div id="header"> <div id="menu">...</div> </div> <!-- Here's where I want my views to be displayed --> <?php echo $content_for_layout ?> <!-- Add a footer to each displayed page --> <div id="footer">...</div> </body> </html> But the problem is that the layout will take effect to all web pages that I have created. Let's see the case that I have recently encountered. In one of the .ctp files, I need to use JQuery function and I need to ass some and tags in the .ctp file. Here are the and tags I used: <Script language="javascript"> $(document).ready(function() { // some functions here }); </Script> <style type="text/css"> { #toppage{ width:800px; } But when I followed the default.ctp file, I noticed that these tags (i.e. and ) happened to appear below the tag. As far as I know, the and self-defined Javascript functions should be put inside the tag of the HTML instead. I have considered to add the and in the default.ctp file, but then these codes would appear in every web pages instead of just a particular web page. Please help.

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  • Delphi 6: How to search a dynamic array for sub-string quickly?

    - by Robert Oschler
    How can I search a dynamic array of char in Delphi 6 for a sub-string and get back an index to a match, not a pointer? I've seen functions in Delphi 6 that do this for strings but not for dynamic char arrays. There is a function called SearchBuf but that function returns a PChar pointer to the match location when what I need is the array index of the match. Thanks.

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