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• What are some things you'd like fresh college grads to know?

  - by bradhe

  So I proposed this to the Reddit community and I'd like to get SO's perspective on this. This is pretty much the copypasta of what I put there. I was thinking about this last night and thought it would be neat to compile a list. I'm still a pretty fresh college grad -- been in industry for 2 years -- but I think that I might have a few interesting things to lend. You don't know as much as you think you do. Somehow, college students think they know a lot more than they do (or maybe that was just me). Likewise, they think they can do more than they actually can. You should fairly assess your skills. QA people are not out to get you. Humans introduce bugs to code. It's not (nescessarily) a personal reflection on you and your skills if your code has a bug and it's caught by the QA/testing team. Listen to your senior (developers). They are not actually fuddy duddies who don't know about the new L337 hax in Ruby (okay, sometimes they are, but still...). They have a wealth of knowledge that you can learn from and it's in your best interest to do so. You will most likely not be doing what you want to for a while. This is mostly true in the corporate world -- startups are a different matter. Also, this is due to more than just the economy, man! Junior devs need to earn their keep, so to speak. Everyone wants to be lead dev on the next project and there are a lot of people in line ahead of you! For every elite developer there are 100 average developers. Joel Spolsky, I'm looking at you. Somehow this concept of ninja coders has really ingrained itself in our culture. While I encourage you to be the best you can be don't be disappointed if people aren't writing blog posts about you in the near future. Anyone else have anything they would see added to this list?

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• Issues in Ajax based applications

  - by Sinuhe

  I'm very interested in developing Ajax based applications. This is, loading almost all of the content of the application via XMLHttpRequest, instead of only some combos and widgets. But if I try to do this form scratch, soon I find some problems without an easy solution. I wonder if there is some framework (both client and server side) to deal with this issues. As far as I know, there isn't (but I've searched mainly in Java world). So I am seriously thinking of doing my own framework, at least for my projects. Therefore, in this question I ask for several things. First, the possible problems of an ajax based development. Then, I'm looking for some framework or utility in order to deal with them. Finally, if there is no framework available, what features must it have. Here are the issues I thought: 1 - JavaScript must be enabled. Security paranoia isn't the only problem: a lot of mobile devices couldn't use the application, too. 2 - Sometimes you need to update more than one DIV (e.g. main content, menu and breadcrumbs). 3 - Unknown response type: when you make an Ajax call, you set the callback function too, usually specifying if expected response is a javascript object or in which DIV put the result. But this fails when you get another type of response: for example when the session has expired and the user must log in again. 4 - Browser's refresh, back and forward buttons can be a real pain. User will expect different behaviors depending on the situation. 5 - When search engines indexes a site, only follow links. Thus, content load by Ajax won't "exist" for who doesn't know about it yet. 6 - Users can ask for open a link in a different window/tab. 7 - Address bar doesn't show the "real" page you are in. So, you can't copy the location and send it to a friend or bookmark the page. 8 - If you want to monetize the site, you can put some advertisings. As you don't refresh entire page and you want to change the ad after some time, you have to refresh only the DIV where the ad is. But this can violate the Terms and Conditions of your ad service. In fact, it can go against AdSense TOS. 9 - When you refresh an entire page, all JavaScript gets "cleaned". But in Ajax calls, all JavaScript objects will remain. 10 - You can't easily change your CSS properties.

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• Moving from Windows to Ubuntu.

  - by djzmo

  Hello there, I used to program in Windows with Microsoft Visual C++ and I need to make some of my portable programs (written in portable C++) to be cross-platform, or at least I can release a working version of my program for both Linux and Windows. I am total newcomer in Linux application development (and rarely use the OS itself). So, today, I installed Ubuntu 10.04 LTS (through Wubi) and equipped Code::Blocks with the g++ compiler as my main weapon. Then I compiled my very first Hello World linux program, and I confused about the output program. I can run my program through the "Build and Run" menu option in Code::Blocks, but when I tried to launch the compiled application externally through a File Browser (in /media/MyNTFSPartition/MyProject/bin/Release; yes, I saved it in my NTFS partition), the program didn't show up. Why? I ran out of idea. I need to change my Windows and Microsoft Visual Studio mindset to Linux and Code::Blocks mindset. So I came up with these questions: How can I execute my compiled linux programs externally (outside IDE)? In Windows, I simply run the generated executable (.exe) file How can I distribute my linux application? In Windows, I simply distribute the executable files with the corresponding DLL files (if any) What is the equivalent of LIBs (static library) and DLLs (dynamic library) in linux and how to use them? In Windows/Visual Studio, I simply add the required libraries to the Additional Dependencies in the Project Settings, and my program will automatically link with the required static library(-ies)/DLLs. Is it possible to use the "binary form" of a C++ library (if provided) so that I wouldn't need to recompile the entire library source code? In Windows, yes. Sometimes precompiled *.lib files are provided. If I want to create a wxWidgets application in Linux, which package should I pick for Ubuntu? wxGTK or wxX11? Can I run wxGTK program under X11? In Windows, I use wxMSW, Of course. If question no. 4 is answered possible, are precompiled wxX11/wxGTK library exists out there? Haven't tried deep google search. In Windows, there is a project called "wxPack" (http://wxpack.sourceforge.net/) that saves a lot of my time. Sorry for asking many questions, but I am really confused on these linux development fundamentals. Any kind of help would be appreciated =) Thanks.

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• Redirecting one file to another using dub2 and strtok

  - by Sergiy Zakharov

  OK, here goes. I have to write a program, in which I need to use strtok and dup2 to redirect one file to another, but I need to also have the user to actually put the command cat < file1 file2, but not from the shell, but instead by using my program. That's why I need strtok. And the reason my program doesn't work is probably because of that, because I don't really understand how strtok works. I found a similar program on the internet, but they just take the ls command and redirect it to the file. That's it. My program is much more complicated. I mean, it would've been easier just to say in shell cat < file1 file2, but for some reason they want us to do it this way. So, anyways, here is what I have so far (here I just combined what I have found on the internet with what I already had from before. We had to do something similar but then the user would just go ls or ls -l. Very simple stuff. This is much harder, for me, at least.) #include <fcntl.h> #include <unistd.h> #include <stdio.h> #include <errno.h> #include <sys/wait.h> #include <string.h> int main() { pid_t pid; char line[256]; char *args[129]; int i; int fd; int status; char *temp; while (1) { printf(">"); if (fgets(line, 256, stdin) == 0) { exit(0); } else { pid = fork(); if (pid == 0) { i = 0; temp = strtok("<",line); while (temp != NULL) { args[i++] = temp; temp = strtok(">",line); args[i] = '\0'; } fd = open("hello", O_RDONLY); dup2(fd, STDIN_FILENO); fd = open("world", O_WRONLY|O_CREAT|O_TRUNC, S_IRWXU); dup2(fd, STDOUT_FILENO ); close(fd); execvp(args[0], args); } else { close(fd); wait(&status); } } } } Any help would be greatly appreciated.

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• are C functions declared in <c____> headers guaranteed to be in the global namespace as well as std?

  - by Evan Teran

  So this is something that I've always wondered but was never quite sure about. So it is strictly a matter of curiosity, not a real problem. As far as I understand, what you do something like #include <cstdlib> everything (except macros of course) are declared in the std:: namespace. Every implementation that I've ever seen does this by doing something like the following: #include <stdlib.h> namespace std { using ::abort; // etc.... } Which of course has the effect of things being in both the global namespace and std. Is this behavior guaranteed? Or is it possible that an implementation could put these things in std but not in the global namespace? The only way I can think of to do that would be to have your libstdc++ implement every c function itself placing them in std directly instead of just including the existing libc headers (because there is no mechanism to remove something from a namespace). Which is of course a lot of effort with little to no benefit. The essence of my question is, is the following program strictly conforming and guaranteed to work? #include <cstdio> int main() { ::printf("hello world\n"); } EDIT: The closest I've found is this (17.4.1.2p4): Except as noted in clauses 18 through 27, the contents of each header cname shall be the same as that of the corresponding header name.h, as specified in ISO/IEC 9899:1990 Programming Languages C (Clause 7), or ISO/IEC:1990 Programming Languages—C AMENDMENT 1: C Integrity, (Clause 7), as appropriate, as if by inclusion. In the C + + Standard Library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope (3.3.5) of the namespace std. which to be honest I could interpret either way. "the contents of each header cname shall be the same as that of the corresponding header name.h, as specified in ISO/IEC 9899:1990 Programming Languages C" tells me that they may be required in the global namespace, but "In the C + + Standard Library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope (3.3.5) of the namespace std." says they are in std (but doesn't specify any other scoped they are in).

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• Understanding C++ dynamic allocation

  - by kiokko89

  Consider the following code: class CString { private: char* buff; size_t len; public: CString(const char* p):len(0), buff(nullptr) { cout << "Constructor called!"<<endl; if (p!=nullptr) { len= strlen(p); if (len>0) { buff= new char[len+1]; strcpy_s(buff, len+1, p); } } } CString (const CString& s) { cout << "Copy constructor called!"<<endl; len= s.len; buff= new char[len+1]; strcpy_s(buff, len+1, s.buff); } CString& operator = (const CString& rhs) { cout << "Assignment operator called!"<<endl; if (this != &rhs) { len= rhs.len; delete[] buff; buff= new char[len+1]; strcpy_s(buff, len+1, rhs.buff); } return *this; } CString operator + (const CString& rhs) const { cout << "Addition operator called!"<<endl; size_t lenght= len+rhs.len+1; char* tmp = new char[lenght]; strcpy_s(tmp, lenght, buff); strcat_s(tmp, lenght, rhs.buff); return CString(tmp); } ~CString() { cout << "Destructor called!"<<endl; delete[] buff; } }; int main() { CString s1("Hello"); CString s2("World"); CString s3 = s1+s2; } My problem is that I don't know how to delete the memory allocated in the addition operator function(char* tmp = new char[length]). I couldn't do this in the constructor(I tried delete[] p) because it is also called from the main function with arrays of chars as parameters which are not allocated on the heap...How can I get around this? (Sorry for my bad English...)

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• Having trouble wrapping functions in the linux kernel

  - by Corey Henderson

  I've written a LKM that implements Trusted Path Execution (TPE) into your kernel: https://github.com/cormander/tpe-lkm I run into an occasional kernel OOPS (describe at the end of this question) when I define WRAP_SYSCALLS to 1, and am at my wit's end trying to track it down. A little background: Since the LSM framework doesn't export its symbols, I had to get creative with how I insert the TPE checking into the running kernel. I wrote a find_symbol_address() function that gives me the address of any function I need, and it works very well. I can call functions like this: int (*my_printk)(const char *fmt, ...); my_printk = find_symbol_address("printk"); (*my_printk)("Hello, world!\n"); And it works fine. I use this method to locate the security_file_mmap, security_file_mprotect, and security_bprm_check functions. I then overwrite those functions with an asm jump to my function to do the TPE check. The problem is, the currently loaded LSM will no longer execute the code for it's hook to that function, because it's been totally hijacked. Here is an example of what I do: int tpe_security_bprm_check(struct linux_binprm *bprm) { int ret = 0; if (bprm->file) { ret = tpe_allow_file(bprm->file); if (IS_ERR(ret)) goto out; } #if WRAP_SYSCALLS stop_my_code(&cs_security_bprm_check); ret = cs_security_bprm_check.ptr(bprm); start_my_code(&cs_security_bprm_check); #endif out: return ret; } Notice the section between the #if WRAP_SYSCALLS section (it's defined as 0 by default). If set to 1, the LSM's hook is called because I write the original code back over the asm jump and call that function, but I run into an occasional kernel OOPS with an "invalid opcode": invalid opcode: 0000 [#1] SMP RIP: 0010:[<ffffffff8117b006>] [<ffffffff8117b006>] security_bprm_check+0x6/0x310 I don't know what the issue is. I've tried several different types of locking methods (see the inside of start/stop_my_code for details) to no avail. To trigger the kernel OOPS, write a simple bash while loop that endlessly starts a backgrounded "ls" command. After a minute or so, it'll happen. I'm testing this on a RHEL6 kernel, also works on Ubuntu 10.04 LTS (2.6.32 x86_64). While this method has been the most successful so far, I have tried another method of simply copying the kernel function to a pointer I created with kmalloc but when I try to execute it, I get: kernel tried to execute NX-protected page - exploit attempt? (uid: 0). If anyone can tell me how to kmalloc space and have it marked as executable, that would also help me solve the above problem. Any help is appreciated!

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• plane bombing problems- help

  - by peiska

  I'm training code problems, and on this one I am having problems to solve it, can you give me some tips how to solve it please. The problem is something like this: Your task is to find the sequence of points on the map that the bomber is expected to travel such that it hits all vital links. A link from A to B is vital when its absence isolates completely A from B. In other words, the only way to go from A to B (or vice versa) is via that link. Notice that if we destroy for example link (d,e), it becomes impossible to go from d to e,m,l or n in any way. A vital link can be hit at any point that lies in its segment (e.g. a hit close to d is as valid as a hit close to e). Of course, only one hit is enough to neutralize a vital link. Moreover, each bomb affects an exact circle of radius R, i.e., every segment that intersects that circle is considered hit. Due to enemy counter-attack, the plane may have to retreat at any moment, so the plane should follow, at each moment, to the closest vital link possible, even if in the end the total distance grows larger. Given all coordinates (the initial position of the plane and the nodes in the map) and the range R, you have to determine the sequence of positions in which the plane has to drop bombs. This sequence should start (takeoff) and finish (landing) at the initial position. Except for the start and finish, all the other positions have to fall exactly in a segment of the map (i.e. it should correspond to a point in a non-hit vital link segment). The coordinate system used will be UTM (Universal Transverse Mercator) northing and easting, which basically corresponds to a Euclidian perspective of the world (X=Easting; Y=Northing). Input Each input file will start with three floating point numbers indicating the X0 and Y0 coordinates of the airport and the range R. The second line contains an integer, N, indicating the number of nodes in the road network graph. Then, the next N (<10000) lines will each contain a pair of floating point numbers indicating the Xi and Yi coordinates (1 No two links will ever cross with each other. Output The program will print the sequence of coordinates (pairs of floating point numbers with exactly one decimal place), each one at a line, in the order that the plane should visit (starting and ending in the airport). Sample input 1 102.3 553.9 0.2 14 342.2 832.5 596.2 638.5 479.7 991.3 720.4 874.8 744.3 1284.1 1294.6 924.2 1467.5 659.6 1802.6 659.6 1686.2 860.7 1548.6 1111.2 1834.4 1054.8 564.4 1442.8 850.1 1460.5 1294.6 1485.1 17 1 2 1 3 2 4 3 4 4 5 4 6 6 7 7 8 8 9 8 10 9 10 10 11 6 11 5 12 5 13 12 13 13 14 Sample output 1 102.3 553.9 720.4 874.8 850.1 1460.5 102.3 553.9

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• Returning JSON in CFFunction and appending it to layer is causing an error

  - by Mel

  I'm using the qTip jQuery plugin to generate a dynamic tooltip. I'm getting an error in my JS, and I'm unsure if its source is the JSON or the JS. The tooltip calls the following function: (sorry about all this code, but it's necessary) <cffunction name="fGameDetails" access="remote" returnType="any" returnformat="JSON" output="false" hint="This grabs game details for the games.cfm page"> <!---Argument, which is the game ID---> <cfargument name="gameID" type="numeric" required="true" hint="CFC will look for GameID and retrieve its details"> <!---Local var---> <cfset var qGameDetails = ""> <!---Database query---> <cfquery name="qGameDetails" datasource="#REQUEST.datasource#"> SELECT titles.titleName AS tName, titles.titleBrief AS tBrief, games.gameID, games.titleID, games.releaseDate AS rDate, genres.genreName AS gName, platforms.platformAbbr AS pAbbr, platforms.platformName AS pName, creviews.cReviewScore AS rScore, ratings.ratingName AS rName FROM games Inner Join platforms ON platforms.platformID = games.platformID Inner Join titles ON titles.titleID = games.titleID Inner Join genres ON genres.genreID = games.genreID Inner Join creviews ON games.gameID = creviews.gameID Inner Join ratings ON ratings.ratingID = games.ratingID WHERE (games.gameID = #ARGUMENTS.gameID#); </cfquery> <cfreturn qGameDetails> </cffunction> This function returns the following JSON: { "COLUMNS": [ "TNAME", "TBRIEF", "GAMEID", "TITLEID", "RDATE", "GNAME", "PABBR", "PNAME", "RSCORE", "RNAME" ], "DATA": [ [ "Dark Void", "Ancient gods known as 'The Watchers,' once banished from our world by superhuman Adepts, have returned with a vengeance.", 154, 54, "January, 19 2010 00:00:00", "Action & Adventure", "PS3", "Playstation 3", 3.3, "14 Anos" ] ] } The problem I'm having is every time I try to append the JSON to the layer #catalog, I get a syntax error that says "missing parenthetical." This is the JavaScript I'm using: $(document).ready(function() { $('#catalog a[href]').each(function() { $(this).qtip( { content: { url: '/gamezilla/resources/components/viewgames.cfc?method=fGameDetails', data: { gameID: $(this).attr('href').match(/gameID=([0-9]+)$/)[1] }, method: 'get' }, api: { beforeContentUpdate: function(content) { var json = eval('(' + content + ')'); content = $('<div />').append( $('<h1 />', { html: json.TNAME })); return content; } }, style: { width: 300, height: 300, padding: 0, name: 'light', tip: { corner: 'leftMiddle', size: { x: 40, y : 40 } } }, position: { corner: { target: 'rightMiddle', tooltip: 'leftMiddle' } } }); }); }); Any ideas where I'm going wrong? I tried many things for several days and I can't find the issue. Many thanks!

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• StaX: Content not allowed in prolog

  - by RalfB

  I have the following (test) XML file below and Java code that uses StaX. I want to apply this code to a file that is about 30 GB large but with fairly small elements, so I thought StaX is a good choice. I am getting the following error: Exception in thread "main" javax.xml.stream.XMLStreamException: ParseError at [row,col]:[1,1] Message: Content is not allowed in prolog at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:598) at at.tuwien.mucke.util.xml.staxtest.StaXTest.main(StaXTest.java:18) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120) <?xml version='1.0' encoding='utf-8'?> <catalog> <book id="bk101"> <author>Gambardella, Matthew</author> <title>XML Developer's Guide</title> <price>44.95</price> <description>An in-depth look at creating applications with XML.</description> </book> <book id="bk102"> <author>Ralls, Kim</author> <title>Midnight Rain</title> <price>5.95</price> <description>A former architect battles corporate zombies, an evil sorceress, and her own childhood to become queen of the world.</description> </book> </catalog> Here the code: package xml.staxtest; import java.io.*; import javax.xml.stream.*; public class StaXTest { public static void main(String[] args) throws Exception { XMLInputFactory xif = XMLInputFactory.newInstance(); XMLStreamReader streamReader = xif.createXMLStreamReader(new FileReader("D:/Data/testFile.xml")); while(streamReader.hasNext()){ int eventType = streamReader.next(); if(eventType == XMLStreamReader.START_ELEMENT){ System.out.println(streamReader.getLocalName()); } //... more to come here later ... } } }

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• Simple html page using Bootstrap

  - by Athashri

  I am writing a simple HTML page using the Twitter Bootstrap. But the navbar and links are rendered as normal HTML on the browser. I have referred to multiple sites but the same steps are given everywhere. I am not sure where I am going wrong. Code: <!DOCTYPE HTML> <html> <head> <meta charset="utf-8"> <link rel= "stylesheet" href= "css/bootstrap.css" type="text/css"> <title> Bootstrap example</title> </head> <body> <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script> <script src="js/bootstrap.js"></script> <h1>Hello, world!</h1> <div class ="container"> <h1><a href="#">Bootstrap Site</a></h1> <div class="navbar"> <div class="navbar-inner"> <div class="container"> <ul class="nav"> <li class="active"><a href="#">Home</a></li> <li><a href="#">Projects</a></li> <li><a href="#">Services</a></li> <li><a href="#">Downloads</a></li> <li><a href="#">About</a></li> <li><a href="#">Contact</a></li> </ul> </div> </div> </div> </div> </body> </html>

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• How to replace an object in an NSMutableArray at a given index with a new object

  - by shakeelw

  Hi guys. I have an NSMutableArray object(retained, synthesized as all) that is initiated just fine and I can easily add objects to it using the 'addObject:' method. But if I want to replace an object at a certain index with a new one in that NSMutableArray, it doesn't work. For example: ClassA.h @interface ClassA : NSObject { NSMutableArray *list; } @property (nonatomic, copy, readwrite) NSMutableArray *list; end ClassA.m import "ClassA.h" @implementation ClassA @synthesize list; (id)init { [super init]; NSMutableArray *localList = [[NSMutableArray alloc] init]; self.list = localList; [localList release]; //Add initial data [list addObject:@"Hello "]; [list addObject:@"World"]; } // Custom set accessor to ensure the new list is mutable (void)setList:(NSMutableArray *)newList { if (list != newList) { [list release]; list = [newList mutableCopy]; } } -(void)updateTitle:(NSString *)newTitle:(NSString *)theIndex { int i = [theIndex intValue]-1; [self.list replaceObjectAtIndex:i withObject:newTitle]; NSLog((NSString *)[self.list objectAtIndex:i]); // gives the correct output } However, the change remains true only inside the method. from any other method, the NSLog((NSString *)[self.list objectAtIndex:i]); gives the same old value. How can I actually get the old object replaced with the new one at a specific index so that the change can be noticed from within any other method as well. I even modified the method like this, but the result is the same: -(void)updateTitle:(NSString *)newTitle:(NSString *)theIndex { int i = [theIndex intValue]-1; NSMutableArray *localList = [[NSMutableArray alloc] init]; localList = [localList mutableCopy]; for(int j = 0; j < [list count]; j++) { if(j == i) { [localList addObject:newTitle]; NSLog(@"j == 1"); NSLog([NSString stringWithFormat:@"%d", j]); } else { [localList addObject:(NSString *)[self.list objectAtIndex:j]]; } } [self.list release]; //self.list = [localList mutableCopy]; [self setList:localList]; [localList release]; } Please help out guys :)

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• [NHibernate and ASP.NET MVC] How can I implement a robust session-per-request pattern in my project,

  - by Guillaume Gervais

  I'm currently building an ASP.NET MVC project, with NHibernate as its persistance layer. For now, some functionnalities have been implemented, but only use local NHibernate sessions: each method that accessed the database (read or write) needs to instanciate its own NHibernate session, with the "using()" directive. The problem is that I want to leverage NHibernate's Lazy-Loading capabilities to improve the performance of my project. This implies an open NHibernate session per request until the view is rendered. Furthermore, simultaneous request must be supported (multiple Sessions at the same time). How can I achieve that as cleanly as possible? I searched the Web a little bit and learned about the session-per-request pattern. Most of the implementations I saw used some sort of Http* (HttpContext, etc.) object to store the session. Also, using the Application_BeginRequest/Application_EndRequest functions is complicated, since they get fired for each HTTP request (aspx files, css files, js files, etc.), when I only want to instanciate a session once per request. The concern that I have is that I don't want my views or controllers to have access to NHibernate sessions (or, more generally, NHibernate namespaces and code). That means that I do not want to handle sessions at the controller level nor the view one. I have a few options in mind. Which one seems the best ? Use interceptors (like in GRAILS) that get triggered before and after the controller action. These would open and close sessions/transactions. Is it possible in the ASP.NET MVC world? Use the CurrentSessionContext Singleton provided by NHibernate in a Web context. Using this page as an example, I think this is quite promising, but that still requires filters at the controller level. Use the HttpContext.Current.Items to store the request session. This, coupled with a few lines of code in Global.asax.cs, can easily provide me with a session on the request level. However, it means that dependencies will be injected between NHibernate and my views (HttpContext). Thank you very much!

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• OpenGL ES Polygon with Normals rendering (Note the 'ES!')

  - by MarqueIV

  Ok... imagine I have a relatively simple solid that has six distinct normals but actually has close to 48 faces (8 faces per direction) and there are a LOT of shared vertices between faces. What's the most efficient way to render that in OpenGL? I know I can place the vertices in an array, then use an index array to render them, but I have to keep breaking my rendering steps down to change the normals (i.e. set normal 1... render 8 faces... set normal 2... render 8 faces, etc.) Because of that I have to maintain an array of index arrays... one for each normal! Not good! The other way I can do it is to use separate normal and vertex arrays (or even interleave them) but that means I need to have a one-to-one ratio for normals to vertices and that means the normals would be duplicated 8 times more than they need to be! On something with a spherical or even curved surface, every normal most likely is different, but for this, it really seems like a waste of memory. In a perfect world I'd like to have my vertex and normal arrays have different lengths, then when I go to draw my triangles or quads To specify the index to each array for that vertex. Now the OBJ file format lets you specify exactly that... a vertex array and a normal array of different lengths, then when you specify the face you are rendering, you specify a vertex and a normal index (as well as a UV coord if you are using textures too) which seems like the perfect solution! 48 vertices but only 8 normals, then pairs of indexes defining the shapes' faces. But I'm not sure how to render that in OpenGL ES (again, note the 'ES'.) Currently I have to 'denormalize' (sorry for the SQL pun there) the normals back to a 1-to-1 with the vertex array, then render. Just wastes memory to me. Anyone help? I hope I'm missing something very simple here. Mark

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• How should I ethically approach user password storage for later plaintext retrieval?

  - by Shane

  As I continue to build more and more websites and web applications I am often asked to store user's passwords in a way that they can be retrieved if/when the user has an issue (either to email a forgotten password link, walk them through over the phone, etc.) When I can I fight bitterly against this practice and I do a lot of ‘extra’ programming to make password resets and administrative assistance possible without storing their actual password. When I can’t fight it (or can’t win) then I always encode the password in some way so that it at least isn’t stored as plaintext in the database—though I am aware that if my DB gets hacked that it won’t take much for the culprit to crack the passwords as well—so that makes me uncomfortable. In a perfect world folks would update passwords frequently and not duplicate them across many different sites—unfortunately I know MANY people that have the same work/home/email/bank password, and have even freely given it to me when they need assistance. I don’t want to be the one responsible for their financial demise if my DB security procedures fail for some reason. Morally and ethically I feel responsible for protecting what can be, for some users, their livelihood even if they are treating it with much less respect. I am certain that there are many avenues to approach and arguments to be made for salting hashes and different encoding options, but is there a single ‘best practice’ when you have to store them? In almost all cases I am using PHP and MySQL if that makes any difference in the way I should handle the specifics. Additional Information for Bounty I want to clarify that I know this is not something you want to have to do and that in most cases refusal to do so is best. I am, however, not looking for a lecture on the merits of taking this approach I am looking for the best steps to take if you do take this approach. In a note below I made the point that websites geared largely toward the elderly, mentally challenged, or very young can become confusing for people when they are asked to perform a secure password recovery routine. Though we may find it simple and mundane in those cases some users need the extra assistance of either having a service tech help them into the system or having it emailed/displayed directly to them. In such systems the attrition rate from these demographics could hobble the application if users were not given this level of access assistance, so please answer with such a setup in mind. Thanks to Everyone This has been a fun questions with lots of debate and I have enjoyed it. In the end I selected an answer that both retains password security (I will not have to keep plain text or recoverable passwords), but also makes it possible for the user base I specified to log into a system without the major drawbacks I have found from normal password recovery. As always there were about 5 answers that I would like to have marked correct for different reasons, but I had to choose the best one--all the rest got a +1. Thanks everyone!

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• Technical non-terminating condition in a loop

  - by Snarfblam

  Most of us know that a loop should not have a non-terminating condition. For example, this C# loop has a non-terminating condition: any even value of i. This is an obvious logic error. void CountByTwosStartingAt(byte i) { // If i is even, it never exceeds 254 for(; i < 255; i += 2) { Console.WriteLine(i); } } Sometimes there are edge cases that are extremely unlikeley, but technically constitute non-exiting conditions (stack overflows and out-of-memory errors aside). Suppose you have a function that counts the number of sequential zeros in a stream: int CountZeros(Stream s) { int total = 0; while(s.ReadByte() == 0) total++; return total; } Now, suppose you feed it this thing: class InfiniteEmptyStream:Stream { // ... Other members ... public override int Read(byte[] buffer, int offset, int count) { Array.Clear(buffer, offset, count); // Output zeros return count; // Never returns -1 (end of stream) } } Or more realistically, maybe a stream that returns data from external hardware, which in certain cases might return lots of zeros (such as a game controller sitting on your desk). Either way we have an infinite loop. This particular non-terminating condition stands out, but sometimes they don't. A completely real-world example as in an app I'm writing. An endless stream of zeros will be deserialized into infinite "empty" objects (until the collection class or GC throws an exception because I've exceeded two billion items). But this would be a completely unexpected circumstance (considering my data source). How important is it to have absolutely no non-terminating conditions? How much does this affect "robustness?" Does it matter if they are only "theoretically" non-terminating (is it okay if an exception represents an implicit terminating condition)? Does it matter whether the app is commercial? If it is publicly distributed? Does it matter if the problematic code is in no way accessible through a public interface/API? Edit: One of the primary concerns I have is unforseen logic errors that can create the non-terminating condition. If, as a rule, you ensure there are no non-terminating conditions, you can identify or handle these logic errors more gracefully, but is it worth it? And when? This is a concern orthogonal to trust.

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• C# Type Casting at Runtimefor Array.SetValue

  - by sprocketonline

  I'm trying to create an array using reflection, and insert values into it. I'm trying to do this for many different types so would like a createAndFillArray function capable of this : Type t1 = typeof(A); Type t2 = typeof(B); double exampleA = 22.5; int exampleB = 43; Array arrA = createAndFillArray(t1, exampleA); Array arrB = createAndFillArray(t2, exampleB); private Array createAndFillArray(Type t, object val){ Array arr = Array.CreateInstance( t, 1); //length 1 in this example only, real-world is of variable length. arr.SetValue( val, 0 ); //this causes the following error: "System.InvalidCastException : Object cannot be stored in an array of this type." return arr; } with the class A being as follows: public class A{ public A(){} private double val; public double Value{ get{ return val; } set{ this.val = value; } } public static implicit operator A(double d){ A a = new A(); a.Value = d; return a; } } and class B being very similar, but with int: public class B{ public B(){} private double val; public double Value{ get{ return val; } set{ this.val = value; } } public static implicit operator B(double d){ B b = new B(); b.Value = d; return b; } } I hoped that the implicit operator would have ensured that the double be converted to class A, or the int to class B, and the error avoided; but this is obviously not so. The above is used in a custom deserialization class, which takes data from a custom data format and fills in the corresponding .Net object properties. I'm doing this via reflection and at runtime, so I think both are unavoidable. I'm targeting the C# 2.0 framework. I've dozens, if not hundreds, of classes similar to A and B, so would prefer to find a solution which improved on the createAndFillArray method rather than a solution which altered these classes.

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• How do I make a GUI that behaves like this?

  - by Karl Knechtel

  This is difficult to explain without illustration, so - behold, an illustration, cobbled together from screenshots of a few hello-world examples and a lot of Paint work: I have started out using Windows Forms on .NET (via IronPython, but that shouldn't be important), and haven't been able to figure out very much. GUI libraries in general are very intimidating, simply because every class has so many possible attributes. Documentation is good at explaining what everything does, but not so good at helping you figure out what you need. I will be assembling the GUI dynamically, but I'm not expecting that to be the hard part. The sticking points for me right now are: How do I get text labels to size themselves automatically to the width of the contained text (so that the text doesn't clip, and I also don't reserve unnecessary space for them when resizing the window)? How do I make the vertical scrollbar always appear? Setting the VScroll property (why is this protected when AutoScroll is public, BTW?) doesn't seem to do anything. How come the horizontal scrollbar is not added by AutoScroll when contents are laid out vertically (via Dock = DockStyle.Top)? I can use a minimum size for panels to prevent the label and corresponding control from overlapping when the window is shrunk horizontally, but then the scrollbar doesn't appear and the control is inaccessible. How can I put limits on window resizing (e.g. set a minimum width) without disabling it completely? (Just set minimum/maximum sizes for the Form?) Related to that, is there any way to set minimum/maximum widths or heights without setting a minimum/maximum size (i.e. can I constrain the size in only one dimension)? Is there a built-in control suitable for hex editing or am I going to have to build something myself? ... And should I be using something else (perhaps something more capable?) I've heard WPF mentioned, but I understand that this involves XML and I really want to build a GUI from XML - I already have data in an object graph, and doing some kind of weird XML pseudo-serialization (in Python, no less!) in order to create a GUI seems incredibly roundabout.

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• jQuery: load refuses to get dynamic content in IE6

  - by user260157

  jQuery refuses to load my dynamic content in IE6. All in FireFox & Safari works fine. Only IE6 is being a pain. When I try the a html with <p>Hello World</p> that works. Properly. But when loading a PHP it doesn't work! As you can see it's doing multiple things. <script type="text/javascript"> // When the document is ready set up our sortable with it's inherant function(s) $(document).ready(function() { // Sort list & amend in database function sortTableMenuAndReload() { var order = $('#menuList').sortable('serialize'); $.post("PLUGINS/SortableMenu/process-sortable.php",order); $("#menuList").load("PLUGINS/SortableMenu/sortableMenu_ajax.php"); } function sortTableOrder() { var order = $('#menuList').sortable('serialize'); $.post("PLUGINS/SortableMenu/process-sortable.php",order); } function sortTableOrderAndRemove(removeID) { $('#listItem_'+removeID).remove(); var order = $('#menuList').sortable('serialize'); $.post("PLUGINS/SortableMenu/process-sortable.php",order); $("#menuList").load("PLUGINS/SortableMenu/sortableMenu_ajax.php"); } $("#menuList > li > .remove").live('click', function () { var removeID = $(this).attr('id'); $.ajax({ type: 'post', url: 'PLUGINS/SortableMenu/removeLine.php', data: 'id='+removeID, success: sortTableOrderAndRemove(removeID) }); }); $("#menuList > li > .publish").live('click', function () { var publishID = $(this).attr('id'); $.ajax({ type: 'post', url: 'PLUGINS/SortableMenu/publishLine.php', data: 'id='+publishID, success: sortTableOrder }); }); $('#new_documents > li').draggable({ addClasses: false, helper:'clone', connectToSortable:'#menuList' }); $("#menuList").droppable({ addClasses: false, drop: function() { var clone = $("#menuList > li#newArticleTYPE1"); $(clone).attr("id","listItem_newArticleTYPE1"); } }); $("#menuList").sortable({ opacity: 0.6, handle : '.handle, .remove', update : sortTableMenuAndReload }); }); </script>

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• What do I need to distribute (keys, certs) for Python w/ SSL-socket connection?

  - by fandingo

  I'm trying to write a generic server-client application that will be able to exchange data amongst servers. I've read over quite a few OpenSSL documents, and I have successfully setup my own CA and created a cert (and private key) for testing purposes. I'm stuck with Python 2.3, so I can't use the standard "ssl" library. Instead, I'm stuck with PyOpenSSL, which doesn't seem bad, but there aren't many documents out there about it. My question isn't really about getting it working. I'm more confused about the certificates and where they need to go. Here are my two programs that do work: Server: #!/bin/env python from OpenSSL import SSL import socket import pickle def verify_cb(conn, cert, errnum, depth, ok): print('Got cert: %s' % cert.get_subject()) return ok ctx = SSL.Context(SSL.TLSv1_METHOD) ctx.set_verify(SSL.VERIFY_PEER|SSL.VERIFY_FAIL_IF_NO_PEER_CERT, verify_cb) # ?????? ctx.use_privatekey_file('./Dmgr-key.pem') ctx.use_certificate_file('Dmgr-cert.pem') # ?????? ctx.load_verify_locations('./CAcert.pem') server = SSL.Connection(ctx, socket.socket(socket.AF_INET, socket.SOCK_STREAM)) server.bind(('', 50000)) server.listen(3) a, b = server.accept() c = a.recv(1024) print(c) Client: from OpenSSL import SSL import socket import pickle def verify_cb(conn, cert, errnum, depth, ok): print('Got cert: %s' % cert.get_subject()) return ok ctx = SSL.Context(SSL.TLSv1_METHOD) ctx.set_verify(SSL.VERIFY_PEER, verify_cb) # ?????????? ctx.use_privatekey_file('/home/justin/code/work/CA/private/Dmgr-key.pem') ctx.use_certificate_file('/home/justin/code/work/CA/Dmgr-cert.pem') # ????????? ctx.load_verify_locations('/home/justin/code/work/CA/CAcert.pem') sock = SSL.Connection(ctx, socket.socket(socket.AF_INET, socket.SOCK_STREAM)) sock.connect(('10.0.0.3', 50000)) a = Tester(2, 2) b = pickle.dumps(a) sock.send("Hello, world") sock.flush() sock.send(b) sock.shutdown() sock.close() I found this information from ftp://ftp.pbone.net/mirror/ftp.pld-linux.org/dists/2.0/PLD/i586/PLD/RPMS/python-pyOpenSSL-examples-0.6-2.i586.rpm which contains some example scripts. As you might gather, I don't fully understand the sections between the " # ????????." I don't get why the certificate and private key are needed on both the client and server. I'm not sure where each should go, but shouldn't I only need to distribute one part of the key (probably the public part)? It undermines the purpose of having asymmetric keys if you still need both on each server, right? I tried alternating removing either the pkey or cert on either box, and I get the following error no matter which I remove: OpenSSL.SSL.Error: [('SSL routines', 'SSL3_READ_BYTES', 'sslv3 alert handshake failure'), ('SSL routines', 'SSL3_WRITE_BYTES', 'ssl handshake failure')] Could someone explain if this is the expected behavior for SSL. Do I really need to distribute the private key and public cert to all my clients? I'm trying to avoid any huge security problems, and leaking private keys would tend to be a big one... Thanks for the help!

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• Getting the responseText from XMLHttpRequest-Object

  - by Sammy46

  I wrote a cgi-script with c++ to return the query-string back to the requesting ajax object. I also write the query-string in a file in order to see if the cgi script works correctly. But when I ask in the html document for the response Text to be shown in a messagebox i get a blank message. here is my code: js: <script type = "text/javascript"> var XMLHttp; if(navigator.appName == "Microsoft Internet Explorer") { XMLHttp = new ActiveXObject("Microsoft.XMLHTTP"); } else { XMLHttp = new XMLHttpRequest(); } function getresponse () { XMLHttp.open ("GET", "http://localhost/cgi-bin/AJAXTest?" + "fname=" + document.getElementById('fname').value + "&sname=" + document.getElementById('sname').value,true); XMLHttp.send(null); } XMLHttp.onreadystatechange=function(){ if(XMLHttp.readyState == 4) { document.getElementById('response_area').innerHTML += XMLHttp.readyState; var x= XMLHttp.responseText alert(x) } } </script> First Names(s)<input onkeydown = "javascript: getresponse ()" id="fname" name="name"> <br> Surname<input onkeydown = "javascript: getresponse();" id="sname"> <div id = "response_area"> </div> C++: int main() { QFile log("log.txt"); if(!log.open(QIODevice::WriteOnly | QIODevice::Text)) { return 1; } QTextStream outLog(&log); QString QUERY_STRING= getenv("QUERY_STRING"); //if(QUERY_STRING!=NULL) //{ cout<<"Content-type: text/plain\n\n" <<"The Query String is: " << QUERY_STRING.toStdString()<< "\n"; outLog<<"Content-type: text/plain\n\n" <<"The Query String is: " <<QUERY_STRING<<endl; //} return 0; } I'm happy about every advice what to do! EDIT: the output to my logfile works just fine: Content-type: text/plain The Query String is: fname=hello&sname=world I just noticed that if i open it with IE8 i get the query-string. But only on the first "keydown" after that IE does nothing.

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• Can't insert a number into a C++ custom streambuf/ostream

  - by 0xbe5077ed

  I have written a custom std::basic_streambuf and std::basic_ostream because I want an output stream that I can get a JNI string from in a manner similar to how you can call std::ostringstream::str(). These classes are quite simple. namespace myns { class jni_utf16_streambuf : public std::basic_streambuf<char16_t> { JNIEnv * d_env; std::vector<char16_t> d_buf; virtual int_type overflow(int_type); public: jni_utf16_streambuf(JNIEnv *); jstring jstr() const; }; typedef std::basic_ostream<char16_t, std::char_traits<char16_t>> utf16_ostream; class jni_utf16_ostream : public utf16_ostream { jni_utf16_streambuf d_buf; public: jni_utf16_ostream(JNIEnv *); jstring jstr() const; }; // ... } // namespace myns In addition, I have made four overloads of operator<<, all in the same namespace: namespace myns { // ... utf16_ostream& operator<<(utf16_ostream&, jstring) throw(std::bad_cast); utf16_ostream& operator<<(utf16_ostream&, const char *); utf16_ostream& operator<<(utf16_ostream&, const jni_utf16_string_region&); jni_utf16_ostream& operator<<(jni_utf16_ostream&, jstring); // ... } // namespace myns The implementation of jni_utf16_streambuf::overflow(int_type) is trivial. It just doubles the buffer width, puts the requested character, and sets the base, put, and end pointers correctly. It is tested and I am quite sure it works. The jni_utf16_ostream works fine inserting unicode characters. For example, this works fine and results in the stream containing "hello, world": myns::jni_utf16_ostream o(env); o << u"hello, wor" << u'l' << u'd'; My problem is as soon as I try to insert an integer value, the stream's bad bit gets set, for example: myns::jni_utf16_ostream o(env); if (o.badbit()) throw "bad bit before"; // does not throw int32_t x(5); o << x; if (o.badbit()) throw "bad bit after"; // throws :( I don't understand why this is happening! Is there some other method on std::basic_streambuf I need to be implementing????

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• Between-request Garbage Collection using Passenger

  - by raphaelcm

  We're using Rails 3.0.7 and REE 1.8.7. Long-term, we will be upgrading, but at the moment it's not feasible. Following the advice of several blog posts, we've been tuning our GC, and have settings that work pretty well. But we would really like to run GC outside of the request-response cycle. I've tried patching Passenger per this post, and using the code supplied in this SO question. In both cases, GC does indeed happen between requests. However, every time the between-request GC happens, I see a bunch of this: MONGODB [INFO] Connecting... MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) Starting the New Relic Agent. Installed New Relic Browser Monitoring middleware SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`scoping` = 'pages' AND `refinery_settings`.`name` = 'use_marketable_urls' LIMIT 1 SQL (0.0ms) BEGIN RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`id` = 1 LIMIT 1 AREL (0.0ms) UPDATE `refinery_settings` SET `value` = '--- \"false\"\n', `callback_proc_as_string` = NULL WHERE `refinery_settings`.`id` = 1 SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` SQL (0.0ms) COMMIT SQL (0.0ms) SHOW TABLES RefinerySetting Load (4.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`scoping` IS NULL AND `refinery_settings`.`name` = 'user_image_sizes' LIMIT 1 SQL (0.0ms) BEGIN RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`id` = 17 LIMIT 1 AREL (0.0ms) UPDATE `refinery_settings` SET `value` = '--- \n:small: 120x120>\n:medium: 280x280>\n:large: 580x580>\n', `callback_proc_as_string` = NULL WHERE `refinery_settings`.`id` = 17 SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` SQL (0.0ms) COMMIT ******** Engine Extend: app/helpers/blog_posts_helper SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (4.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES ******** Engine Extend: app/models/user SQL (0.0ms) describe `roles_users` SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (4.0ms) describe `roles_users` SQL (0.0ms) SHOW TABLES SQL (4.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES (etc, etc, etc) Which is what happens when rails "loads the world" when the app starts up. Basically, GC.start is re-loading the app for some reason. Because of this, between-request GC is much slower than inline GC. Is there a way around this? I would love to have snappy, between-request GC if possible. Thanks.

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• Get content in iframe to use as much space as it needs

  - by Mark

  I'm trying to write a simple JavaScript based modal dialog. The JavaScript function takes the content, puts it in a new iframe and adds the iframe to the page. Works great so far, the only problem is that the content of the dialog (e.g. a table) gets wrapped, although plenty of space is available on the page. I'd like the content of the dialog, a table in my case, to use as much space as it needs, without wrapping any lines. I tried lots of combinations of setting width/style.width on the iframe and the table. Nothing did the trick. Here the code to show the iframe dialog: function SimpleDialog() { this.domElement = document.createElement('iframe'); this.domElement.setAttribute('style', 'border: 1px solid red; z-index: 201; position: absolute; top: 0px; left: 0px;'); this.showWithContent = function(content) { document.getElementsByTagName('body')[0].appendChild(this.domElement); this.domElement.contentDocument.body.appendChild(content); var contentBody = this.domElement.contentDocument.body; contentBody.style.padding = '0px'; contentBody.style.margin = '0px'; // Set the iframe size to the size of content. // However, content got wrapped already. this.domElement.style.height = content.offsetHeight + 'px'; this.domElement.style.width = content.offsetWidth + 'px'; this._centerOnScreen(); }; this._centerOnScreen = function() { this.domElement.style.left = window.pageXOffset + (window.innerWidth / 2) - (this.domElement.offsetWidth / 2) + 'px'; this.domElement.style.top = window.pageYOffset + (window.innerHeight / 2) - (this.domElement.offsetHeight / 2) + 'px'; }; } Here the test code: var table = document.createElement('table'); table.setAttribute('style', 'border: 1px solid black; width: 100%;'); table.innerHTML = "<tr><td style='font-size:40px;'>Hello world in big letters</td></tr><tr><td>second row</td></tr>"; var dialog = new SimpleDialog(); dialog.showWithContent(table); The table shows up nicely centered on the page, but the words in the first cell are wrapped to two lines. How do I get the table to use as much space as it needs (without using white-space: nowrap ;) Thanks in advance for any suggestions! -Mark

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• Big Oh Notation - formal definition.

  - by aloh

  I'm reading a textbook right now for my Java III class. We're reading about Big-Oh and I'm a little confused by its formal definition. Formal Definition: "A function f(n) is of order at most g(n) - that is, f(n) = O(g(n)) - if a positive real number c and positive integer N exist such that f(n) <= c g(n) for all n = N. That is, c g(n) is an upper bound on f(n) when n is sufficiently large." Ok, that makes sense. But hold on, keep reading...the book gave me this example: "In segment 9.14, we said that an algorithm that uses 5n + 3 operations is O(n). We now can show that 5n + 3 = O(n) by using the formal definition of Big Oh. When n = 3, 5n + 3 <= 5n + n = 6n. Thus, if we let f(n) = 5n + 3, g(n) = n, c = 6, N = 3, we have shown that f(n) <= 6 g(n) for n = 3, or 5n + 3 = O(n). That is, if an algorithm requires time directly proportional to 5n + 3, it is O(n)." Ok, this kind of makes sense to me. They're saying that if n = 3 or greater, 5n + 3 takes less time than if n was less than 3 - thus 5n + n = 6n - right? Makes sense, since if n was 2, 5n + 3 = 13 while 6n = 12 but when n is 3 or greater 5n + 3 will always be less than or equal to 6n. Here's where I get confused. They give me another example: Example 2: "Let's show that 4n^2 + 50n - 10 = O(n^2). It is easy to see that: 4n^2 + 50n - 10 <= 4n^2 + 50n for any n. Since 50n <= 50n^2 for n = 50, 4n^2 + 50n - 10 <= 4n^2 + 50n^2 = 54n^2 for n = 50. Thus, with c = 54 and N = 50, we have shown that 4n^2 + 50n - 10 = O(n^2)." This statement doesn't make sense: 50n <= 50n^2 for n = 50. Isn't any n going to make the 50n less than 50n^2? Not just greater than or equal to 50? Why did they even mention that 50n <= 50n^2? What does that have to do with the problem? Also, 4n^2 + 50n - 10 <= 4n^2 + 50n^2 = 54n^2 for n = 50 is going to be true no matter what n is. And how in the world does picking numbers show that f(n) = O(g(n))? Please help me understand! :(

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