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• XPath expression exception

  - by fftoolbar

  Hi I am not really sure if i am doing this right with XPath expression. I am trying to locate a text on DOM and this text is assingned to a variable. I have text stored in SQLite and i have retrievd the text and i am trying to locate it on the webpage which actually contains the text. so i ahve the following code: var searchText = dataset[x]['selectedText']; alert(dataset[x]['selectedText']); var res = googbar_frames[0].contentDocument.evaluate("//*[.=searchText]",googbar_frames[0].contentDocument.body,null,XPathResult.ANY_TYPE,null); alert(res.snapshotLength); And i get the following error. Error: Permission denied for <http://en.wikipedia.org> to call method XPathException.toString on <>. Error: Permission denied for <http://en.wikipedia.org> to call method XPathException.toString on <>. Have got the expression correct. I am trying to look for the text on DOM. Or am i going wrong somwehere? cheers

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• passing multidimensional arrays to function

  - by Pegah

  hi! I have a method in my class which uses a 3dimensional tfpairexp as input parameter. and I need to use the values in tfpairexp later. void calctfpairexp (int tf1, int tf2, double tfpairexp[][2][3]) { int ctr,c; for (int j = 0; j < cchips && (c = chips[j].crepls); j += c) { int ctrl_no=0; for (int *p = chips[j].ctrl ; p && (ctr=*p)>=0; ++p,ctrl_no++) { for (int k = 0; k < c; ++k) { tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); } } } } I call the method inside the class like this: calctfpairexp(tf1,tf2,tfpairexp); and I need to use values inside tfpairexp in next lines. but the compiler gives error in this line: tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); and says that the tfpairexp variable is not defined in the calctfpairexp function. any idea?

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• What C++ templates issue is going on with this error?

  - by WilliamKF

  Running gcc v3.4.6 on the Botan v1.8.8 I get the following compile time error building my application after successfully building Botan and running its self test: ../../src/Botan-1.8.8/build/include/botan/secmem.h: In member function `Botan::MemoryVector<T>& Botan::MemoryVector<T>::operator=(const Botan::MemoryRegion<T>&)': ../../src/Botan-1.8.8/build/include/botan/secmem.h:310: error: missing template arguments before '(' token What is this compiler error telling me? Here is a snippet of secmem.h that includes line 130: [...] /** * This class represents variable length buffers that do not * make use of memory locking. */ template<typename T> class MemoryVector : public MemoryRegion<T> { public: /** * Copy the contents of another buffer into this buffer. * @param in the buffer to copy the contents from * @return a reference to *this */ MemoryVector<T>& operator=(const MemoryRegion<T>& in) { if(this != &in) set(in); return (*this); } // This is line 130! [...]

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• jsf, richfaces, popup window

  - by Hubidubi

  Hi I would like to make a list-detail view with richfaces. There will be a link for every record in the list that should open a new window containing record details. I tried to implement the link this way: <a4j:commandLink oncomplete="window.open('/pages/serviceDetail.jsf','popupWindow', 'dependent=yes, menubar=no, toolbar=no, height=500, width=400')" actionListener="#{monitoringBean.recordDetail}" value="details" /> I use <a4j:keepAlive beanName="monitoringBean" ajaxOnly="false" /> for both the list and the detail page. recordDetail method fills the data of the selected record to a variable of the bean that I would like to display on the detail page. The problem is that keepalive doesn't work, so I get new bean instance on the detail page every time. So the the previously selected record from the other bean is not accessible here. Is there a way to pass parameter (id) to the detail page to handle record selection. Or is there any way to make keepalive work? (I this this would be the easiest). Thanks

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• Using Uploadify, I'm renaming uploaded files via uploadify.php, how do I get the check script to now check for this renamed file??

  - by Rob Macintosh

  I've modified my uploadify.php file to rename my uploaded files, i'm appending them with my clients company name. As you can see i'm using scriptData to set the company name, so that uploadify.php can use it. documents.php 'scriptData': { 'PHPSESSID': '<?php echo session_id();?>', 'client_company': '<?php echo $_SESSION['company'] . "-";?>' }, This all works great - but now it breaks my check.php. I'm using the default check script, but now it simply thinks the file doesn't exist, so it overwrites it. I've tried appending the client_company POST variable to the file check; check.php $fileArray = array(); foreach ($_POST as $key => $value) { if ($key != 'folder') { if (file_exists($_SERVER['DOCUMENT_ROOT'] . $_POST['folder'] . '/' . $_POST['client_company'] . $value)) { $fileArray[$key] = $value; } } } echo json_encode($fileArray); But it doesn't work :( Can anyone help?

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• iPhone and iPad : Doing a "select * from something" query in a SQLite database

  - by Abramodj

  Hi folks, i'm trying to use the SQLite data base in my iPad app, and here's my function to make a query: - (void)executeQuery:(char*)query { NSString *file = [self getWritableDBPath]; NSFileManager *fileManager = [NSFileManager defaultManager]; BOOL success = [fileManager fileExistsAtPath:file]; // If its not a local copy set it to the bundle copy if(!success) { //file = [[NSBundle mainBundle] pathForResource:DATABASE_TITLE ofType:@"db"]; [self createEditableCopyOfDatabaseIfNeeded]; } dataArray = NULL; dataArray = [NSMutableArray array]; sqlite3 *database = NULL; if (sqlite3_open([file UTF8String], &database) == SQLITE_OK) { sqlite3_exec(database, query, loadTimesCallback, dataArray, NULL); } sqlite3_close(database); [self logResults]; } if I call [self executeQuery:"select name from table1"]; everything is working fine. But if i call [self executeQuery:"select * from cars"]; the app crashes telling me that the NSMutableArray dataArray is not the right kind of variable where to set the query results. So, how can i do a "select * form table1" query, and store the results? Thanks! EDIT: Here's my loadTimesCallback method: static int loadTimesCallback(void *context, int count, char **values, char **columns) { NSMutableArray *times = (NSMutableArray *)context; for (int i=0; i < count; i++) { const char *nameCString = values[i]; [times addObject:[NSString stringWithUTF8String:nameCString]]; } return SQLITE_OK; }

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• Semi-generic function

  - by Fredrik Ullner

  I have a bunch of overloaded functions that operate on certain data types such as int, double and strings. Most of these functions perform the same action, where only a specific set of data types are allowed. That means I cannot create a simple generic template function as I lose type safety (and potentially incurring a run-time problem for validation within the function). Is it possible to create a "semi-generic compile time type safe function"? If so, how? If not, is this something that will come up in C++0x? An (non-valid) idea; template <typename T, restrict: int, std::string > void foo(T bar); ... foo((int)0); // OK foo((std::string)"foobar"); // OK foo((double)0.0); // Compile Error Note: I realize I could create a class that has overloaded constructors and assignment operators and pass a variable of that class instead to the function.

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• Is there a way to get the PREMATCH ($`) and POSTMATCH ($') from pcrecpp?

  - by Eric Peers

  Is there a way to obtain the C++ equivalent of Perl's PREMATCH ($`) and POSTMATCH ($') from pcrecpp? I would be happy with a string, a char *, or pairs indices/startpos+length that point at this. StringPiece seems like it might accomplish part of this, but I'm not certain how to get it. in perl: $_ = "Hello world"; if (/lo\s/) { $pre = $`; #should be "Hel" $post = $'; #should be "world" } in C++ I would have something like: string mystr = "Hello world"; //do I need to map this in a StringPiece? if (pcrecpp::RE("lo\s").PartialMatch(mystr)) { //should I use Consume or FindAndConsume? //What should I do here to get pre+post matches??? } pcre plainjane c seems to have the ability to return the vector with the matches including the "end" portion of the string, so I could theoretically extract such a pre/post variable, but that seems like a lot of work. I like the simplicty of the pcrecpp interface. Suggestions? Thanks! --Eric

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• How to check if a node's value in one XML is present in another XML with a specific attribute?

  - by Manish

  The question seems to be little confusing. So let me describe my situation through an example: Suppose I have an XML: A.xml <Cakes> <Cake>Egg</Cake> <Cake>Banana</Cake> </Cakes> Another XML: B.xml <Cakes> <Cake show="true">Egg</Cake> <Cake show="true">Strawberry</Cake> <Cake show="false">Banana</Cake> </Cakes> Now I want to show some text say "TRUE" if all the Cake in A.xml have show="true" in B.xml else "FALSE". In the above case, it will print FALSE. I need to develop an XSL for that. I can loop through all the Cake in A.xml and check if that cake has show="true" in B.xml but I don't know how to break in between (and set a variable) if a show="false" is found. Is it possible? Any help/comments appreciated.

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• final transient fields and serialization

  - by doublep

  Is it possible to have final transient fields that are set to any non-default value after serialization in Java? My usecase is a cache variable — that's why it is transient. I also have a habit of making Map fields that won't be changed (i.e. contents of the map is changed, but object itself remains the same) final. However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but null after unserialization. I tried the following, without success: simple field initialization (shown in the example): this is what I normally do, but the initialization doesn't seem to happen after unserialization; initialization in constructor (I believe this is semantically the same as above though); assigning the field in readObject() — cannot be done since the field is final. In the example cache is public only for testing. import java.io.*; import java.util.*; public class test { public static void main (String[] args) throws Exception { X x = new X (); System.out.println (x + " " + x.cache); ByteArrayOutputStream buffer = new ByteArrayOutputStream (); new ObjectOutputStream (buffer).writeObject (x); x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject (); System.out.println (x + " " + x.cache); } public static class X implements Serializable { public final transient Map <Object, Object> cache = new HashMap <Object, Object> (); } } Output: test$X@1a46e30 {} test$X@190d11 null

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• Getting ellipses function parameters without an initial argument

  - by Tox1k

  So I've been making a custom parser for a scripting language, and I wanted to be able to pass only ellipses arguments. I don't need or want an initial variable, however Microsoft and C seem to want something else. FYI, see bottom for info. I've looked at the va_* definitions #define _crt_va_start(ap,v) ( ap = (va_list)_ADDRESSOF(v) + _INTSIZEOF(v) ) #define _crt_va_arg(ap,t) ( *(t *)((ap += _INTSIZEOF(t)) - _INTSIZEOF(t)) ) #define _crt_va_end(ap) ( ap = (va_list)0 ) and the part I don't want is the v in va_start. As a little background I'm competent in goasm and I know how the stack works so I know what's happening here. I was wondering if there is a way to get the function stack base without having to use inline assembly. Ideas I've had: #define im_va_start(ap) (__asm { mov [ap], ebp }) and etc... but really I feel like that's messy and I'm doing it wrong. struct function_table { const char* fname; (void)(*fptr)(...); unsigned char maxArgs; }; function_table mytable[] = { { "MessageBox", &tMessageBoxA, 4 } }; ... some function that sorts through a const char* passed to it to find the matching function in mytable and calls tMessageBoxA with the params. Also, the maxArgs argument is just so I can check that a valid number of parameters is being sent. I have personal reasons for not wanting to send it in the function, but in the meantime we can just say it's because I'm curious. This is just an example; custom libraries are what I would be implementing so it wouldn't just be calling WinAPI stuff. void tMessageBoxA(...) { // stuff to load args passed MessageBoxA(arg1, arg2, arg3, arg4); } I'm using the __cdecl calling convention and I've looked up ways to reliably get a pointer to the base of the stack (not the top) but I can't seem to find any. Also, I'm not worried about function security or typechecking.

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• Disabling repeating keyboard down event in as3

  - by psy-sci

  now I'm trying to make the keyboard events to stop repeating. My idea was to have a true and false condition for when the key is pressed so that it wont repeat if the key is down already. //Mouse Event Over keyCButton.addEventListener(MouseEvent.MOUSE_OVER, function(){gotoAndStop(2)}); //Variable var Qkey:uint = 81; //Key Down Event stage.addEventListener(KeyboardEvent.KEY_DOWN, keydown); var soundplayed = false; function keydown(event:KeyboardEvent){ if (event.keyCode==Qkey) { this.soundplayed=true;} } if (this.soundplayed==false){ gotoAndPlay(3); } else {} //Key Up Event stage.addEventListener(KeyboardEvent.KEY_UP, keyup); function keyup(event:KeyboardEvent){ if (event.keyCode==Qkey) { this.soundplayed=true; gotoAndStop(1); } } doing this just turns off the key event I think i need to add a "&& keyDown..." to "if (this.soundplayed==true)" but i dont know how to do it without getting errors here is the keyboard player i'm trying to fix http://soulseekrecords.org/psysci/animation/piano.html

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• using 'or' operator not working for menu

  - by John Wilkes

  In my code here, I have a CSS class called "active" which I use if the $_GET['page'] == tutorials, php, mysql, etc... The problem is, even if the 'page' variable is not equal to any of these values, the Tutorials button in this case is still active for some reason. Any ideas why this would be happening? Am I using the 'or' (||) operand incorrectly? <?php if($_GET['page'] == 'tutorials' || 'php' || 'mysql' || 'html' || 'css' || 'js') { ?> <li class="active"> <?php } else { ?> <li> <?php } ?> <a href="index.php?page=tutorials">Tutorials</a> <ul> <li><a href="index.php?page=php">PHP</a></li> <li><a href="index.php?page=mysql">MySQL</a></li> <li><a href="index.php?page=html">HTML</a></li> <li><a href="index.php?page=css">CSS</a></li> <li><a href="index.php?page=js">JS</a></li> </ul> </li>

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• PHP.ini Settings Are Ignored By PHP5.3.5 Running With Windows 7 And Apache 2.2.15

  - by Andy

  I did an install of PHP5.3.5 on Windows 7 Home Premium using the MSI installer download. I got it to overwrite a previous version of PHP5 in C:\php5\ When first testing it, the server failed to start. I fixed this by adding the path to PHP in the Apache2.2 httpd file where the installer had inserted 2 lines of coded pointing to the ini file directory and the PHP DLL but had left out the directory path. After doing this, the server starts ok and I can run phpinfo to view the PHP settings in my web browser on local host. In the phpinfo it states that the loaded configuration file is C:\php5\php.ini as expected. But if I make any changes to the settings, and reboot the server, none of the changes are reflected in phpinfo. Yes, I do refresh the browser window. If I rename the php.ini to something else to make it invisible phpinfo then correctly identifies that there is no php.ini file loaded. So the settings in php.ini are being ignored and some default settings are being used (but I have no idea where these are derived from). As far as I can tell, there are no other php.ini files on my computer. In phpinfo it states that the Configuration File (php.ini) Path is C:\Windows but this is the same as on a Windows XP computer that I work on. And in the windows folder I don't see any php.ini file. In the windows registry, there is no mention of PHP5, and the PATH environment variable starts with C:\php5\; So hopefully someone can suggest how I can get PHP5 to take notice of the C:\php5\php.ini settings. :)

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• Safari and Chrome back button changes hidden and submit values in forms

  - by OverClocked

  The following problem happens on both Safari and Chrome, so probably a WebKit issue. Page A: a page that requires you to login to see, contains a form that has a type=submit button, with name=submit, and value=a Page B: some other page Page C: ask user to login page, contains a form with a type=submit button, with name=submit and value=c User visits page A, then page B. Then idles and the user's login session times out. User hits back button to go back to page A. Browser redirects user to page C. On Safari and Chrome, when C is rendered, the form on page C has the type=submit button, name=submit, but value shows up as "a". If you reload while on page C, "c" appears as the value of the name=submit button. The same problem appears with type=hidden input fields; when user hits back button, their values are also changed to some other value from some other form. Also, this problem also shows up w/o the redirect, with just submit then back. In this case the previous page renders with incorrect values for hidden and submit CGI variables. So far the only fix I can come up with is use Javascript to reset the type=hidden and type=submit variable values, after page C loads, to make sure the values are correct. But that's not clean and universally applicable. Short of WebKit fixing this error, has anyone ran into a better workaround? Thanks.

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• Tokenizing numbers for a parser

  - by René Nyffenegger

  I am writing my first parser and have a few questions conerning the tokenizer. Basically, my tokenizer exposes a nextToken() function that is supposed to return the next token. These tokens are distinguished by a token-type. I think it would make sense to have the following token-types: SYMBOL (such as <, :=, ( and the like REMARK (or a comment) NUMBER IDENT (such as the name of a function or a variable) STRING (Something enclosed between "....") Now, do you think this makes sense? Also, I am struggling with the NUMBER token-type. Do you think it makes more sense to further split it up into a NUMBER and a FLOAT token-type? Without a FLOAT token-type, I'd receive NUMBER (eg 402), a SYMBOL (.) followed by another NUMBER (eg 203) if I were about to parse a float. Finally, what do you think makes more sense for the tokenizer to return when it encounters a -909? Should it return the SYMBOL - first, followed by the NUMBER 909 or should it return a NUMBER -909 right away?

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• Simple average calculation

  - by sasquatch90

  I'm trying to write program calculating average of given numbers stored in an array. Amount of numbers should be not more than 100, and user should input them until a !int variable is given : #include <iostream> #include <conio.h> using namespace std; double average(int tab[], int i){ int sum=0; for(int j=0; j<i; ++j){ sum+=tab[j]; } return (double)sum/i; } int main() { int tab[100]; int n=0; int number=0; do { if(n < 100){ cout << "Give " << n+1 << " number : "; cin >> number; tab[n]=number; number=0; ++n; } else{ break; } } while( !isdigit(number) ); cout << average(tab, n) << endl; getch(); return 0; } Why after giving char, it prints me 'Give n number:' for all empty cells of my array ? It should end and use only given numbers.

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• Setting <td> value using jquery

  - by timk

  Hello, I have the div structure shown below. For the second <td> in the table i want to replace &nbsp; with a hyperlink whose href attribute is stored in the variable myLink. How can i do this with jquery ? Please help. Thank You. <div class="pbHeader"> <table cellspacing="0" cellpadding="0" border="0"> <tbody> <tr> <td class="pbTitle"> <h2 class="mainTitle">Transfer Membership</h2> </td> <td> &nbsp; </td> </tr> </tbody> </table> </div>

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• How to read the birthday_date from the Facebook API

  - by Steve

  I have been chasing my tail on this! And it should be so simple!! I have an app in FaceBook that is working fine. However, I need to get the user's birth date. I have successfully got the request for extended permissions, but cannot get the birthday_date out and into a variable/store in database. <?php require_once('facebook.php'); $facebook = new Facebook(array( 'appId' => 'xxxxx', 'secret' => 'yyyyyyy', 'cookie' => true )); if ($facebook->getSession()) { $uid = $facebook->getUser(); $fbme = $facebook->api('/me'); } else { $params = array( 'fbconnect'=>0, 'canvas'=>1, 'req_perms'=>'publish_stream','email','user_location','user_birthday' ); $loginUrl = $facebook->getLoginUrl($params); print "<script type='text/javascript'>top.location.href = '$loginUrl';</script>"; } $session = $facebook->getSession(); $token = $session['access_token']; I would be very grateful if someone could show me the PHP code that reads the extended permissions and places the results into variables. Thanks Steve

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• How to make a self contained jQuery plugin that finds the tallest image height?

  - by Jannis

  I have been trying to make this to be a little jQuery plugin that I can reuse in the future without having to write the following into my actions.js file in full. This works when loaded in the same file where I set the height using my variable tallest. var tallest = null; $('.slideshow img').each(function(index) { if ($(this).height() >= tallest ) { tallest = $(this).height(); } }); $('.slideshow').height(tallest); This works and will cycle through all the items, then set the value of tallest to the greatest height found. The following however does not work: This would be the plugin, loaded from its own file (before the actions.js file that contains the parts using this): (function($){ $.fn.extend({ tallest: function() { var tallest = null; return this.each(function() { if ($(this).height() >= tallest ) { tallest = $(this).height(); } }); } }); })(jQuery); Once loaded I am trying to use it as follows: $('.slideshow img').tallest(); $('.slideshow').height(tallest); However the above two lines return an error of 'tallest is undefined'. How can I make this work? Any ideas would be appreciated. Thinking about this even more the perfect usage of this would be as follows: $('.container').height(tallest('.container item')); But I wouldn't even know where to begin to get this to work in the manner that you pass the object to be measured into the function by adding it into the brackets of the function name. Thanks for reading, Jannis

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• How stop mp3 playing started with audioplayer

  - by bucche

  Hi, My application consists of a table view. row1, row2, row3.... When a cell is touched a different mp3 starts to play (row1.mp3, row2.mp3, row3.mp3....). it works! but i have a problem: i am not able to stop previous mp3, so if i touch a second cell i have 2 mp3s playing... if i touch a third cell i have 3 mp3s and so on... i want to stop mp3 that started before and play mp3 that is related to touched cell... during my tries, i created a variable to show some alerts if the player plays or not and when i am "inside the if" i used [myAudioPlayer stop].. i see the correct alert but mp3 doesn't stop. here is my code - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { NSArray *elementi = [[array objectAtIndex:indexPath.row] componentsSeparatedByString:@"|"]; NSURL *url = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%@.mp3", [[NSBundle mainBundle] resourcePath],[elementi objectAtIndex:1]]]; NSError *error; myAudioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:&error]; myAudioPlayer.numberOfLoops = -1; if (inEsecuzione == 0) { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"1" message:@"1" delegate:nil cancelButtonTitle:@"OK"otherButtonTitles:nil]; [alert show]; [alert release]; [myAudioPlayer play]; inEsecuzione = 1; } else { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"2" message:@"2" delegate:nil cancelButtonTitle:@"OK"otherButtonTitles:nil]; [alert show]; [alert release]; [myAudioPlayer stop]; inEsecuzione = 0; } } as i wrote before, i am not able to stop previous mp3

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• c program pointer

  - by sandy101

  Hello , I am trying some programs in c face a problem with this program #include<stdio.h> int main() { int a=9,*x; float b=3.6,*y; char c='a',*z; printf("the value is %d\n",a); printf("the value is %f\n",b); printf("the value is %c\n",c); x=&a; y=&b; z=&c; printf("%u\n",a); printf("%u\n",b); printf("%u\n",c); x++; y++; z++; printf("%u\n",a); printf("%u\n",b); printf("%u\n",c); return 0; } can any one tell me what is the problem with this and i also want to know that when in the above case if the pointer value is incremented then will it over write the previous value address as suppose that the value we got in the above program (without the increment in the pointer value )is 65524 65520 65519 and after the increment the value of the pointer is 65526(as 2 increment for the int ) 65524(as 4 increment for the float ) 65520(as 1 increment for the char variable ) then if in that case will the new pointer address overwrite the content of the previous address and what value be contained at the new address ......plz help

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• C# XML node with colon

  - by Sticky

  Hi, my code attempts to grab data from the RSS feed of a website. It grabs the nodes fine, but when attempting to grab the data from a node with a colon, it crashes and gives the error "Namespace Manager or XsltContext needed. This query has a prefix, variable, or user-defined function." The code is shown below: WebRequest request = WebRequest.Create("http://buypoe.com/external.php?type=RSS2&lastpost=true"); WebResponse response = request.GetResponse(); StringBuilder sb = new StringBuilder(""); System.IO.StreamReader rssStream = new System.IO.StreamReader(response.GetResponseStream(), System.Text.Encoding.GetEncoding("utf-8")); XmlDocument rssDoc = new XmlDocument(); rssDoc.Load(rssStream); XmlNodeList rssItems = rssDoc.SelectNodes("rss/channel/item"); for (int i = 0; i < 5; i++) { XmlNode rssDetail; rssDetail = rssItems.Item(i).SelectSingleNode("dc:creator"); if (rssDetail != null) { user = rssDetail.InnerText; } else { user = ""; } } I understand that I need to define the namespace, but am unsure how to do this. Help would be appreciated.

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• Why does this Haskell code produce the "infinite type" error?

  - by Charlie Flowers

  I am new to Haskell and facing a "cannot construct infinite type" error that I cannot make sense of. In fact, beyond that, I have not been able to find a good explanation of what this error even means, so if you could go beyond my basic question and explain the "infinite type" error, I'd really appreciate it. Here's the code: intersperse :: a -> [[a]] -> [a] -- intersperse '*' ["foo","bar","baz","quux"] -- should produce the following: -- "foo*bar*baz*quux" -- intersperse -99 [ [1,2,3],[4,5,6],[7,8,9]] -- should produce the following: -- [1,2,3,-99,4,5,6,-99,7,8,9] intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:y:xs) = x:s:y:intersperse s xs And here's the error trying to load it into the interpreter: Prelude :load ./chapter.3.ending.real.world.haskell.exercises.hs [1 of 1] Compiling Main ( chapter.3.ending.real.world.haskell.exercises.hs, interpreted ) chapter.3.ending.real.world.haskell.exercises.hs:147:0: Occurs check: cannot construct the infinite type: a = [a] When generalising the type(s) for `intersperse' Failed, modules loaded: none. Thanks. EDIT: Thanks to the responses, I have corrected the code and I also have a general guideline for dealing with the "infinite type" error in Haskell: Corrected code intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:xs) = x ++ s:intersperse s xs What the problem was: My type signature states that the second parameter to intersperse is a list of lists. Therefore, when I pattern matched against "s (x:y:xs)", x and y became lists. And yet I was treating x and y as elements, not lists. Guideline for dealing with the "infinite type" error: Most of the time, when you get this error, you have forgotten the types of the various variables you're dealing with, and you have attempted to use a variable as if it were some other type than what it is. Look carefully at what type everything is versus how you're using it, and this will usually uncover the problem.

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• Recursive Enumeration in Java

  - by Harm De Weirdt

  Hello everyone. I still have a question about Enumerations. Here's a quick sketch of the situation. I have a class Backpack that has a Hashmap content with as keys a variable of type long, and as value an ArrayList with Items. I have to write an Enumeration that iterates over the content of a Backpack. But here's the catch: in a Backpack, there can also be another Backpack. And the Enumeration should also be able to iterate over the content of a backpack that is in the backpack. (I hope you can follow, I'm not really good at explaining..) Here is the code I have: public Enumeration<Object> getEnumeration() { return new Enumeration<Object>() { private int itemsDone = 0; //I make a new array with all the values of the HashMap, so I can use //them in nextElement() Collection<Long> keysCollection = getContent().keySet(); Long [] keys = keysCollection.toArray(new Long[keysCollection.size()]); public boolean hasMoreElements() { if(itemsDone < getContent().size()) { return true; }else { return false; } } public Object nextElement() { ArrayList<Item> temporaryList= getContent().get(keys[itemsDone]); for(int i = 0; i < temporaryList.size(); i++) { if(temporaryList.get(i) instanceof Backpack) { return temporaryList.get(i).getEnumeration(); }else { return getContent().get(keys[itemsDone++]); } } } }; Will this code work decently? It's just the "return temporaryList.get(i).getEnumeration();" I'm worried about. Will the users still be able to use just the hasMoreElemens() and nextElement() like he would normally do? Any help is appreciated, Harm De Weirdt

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