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• How to combine two rows and calculate the time difference between two timestamp values in MySQL?

  - by Nadar

  I have a situation that I'm sure is quite common and it's really bothering me that I can't figure out how to do it or what to search for to find a relevant example/solution. I'm relatively new to MySQL (have been using MSSQL and PostgreSQL earlier) and every approach I can think of is blocked by some feature lacking in MySQL. I have a "log" table that simply lists many different events with their timestamp (stored as datetime type). There's lots of data and columns in the table not relevant to this problem, so lets say we have a simple table like this: CREATE TABLE log ( id INT NOT NULL AUTO_INCREMENT, name VARCHAR(16), ts DATETIME NOT NULL, eventtype VARCHAR(25), PRIMARY KEY (id) ) Let's say that some rows have an eventtype = 'start' and others have an eventtype = 'stop'. What I want to do is to somehow couple each "startrow" with each "stoprow" and find the time difference between the two (and then sum the durations per each name, but that's not where the problem lies). Each "start" event should have a corresponding "stop" event occuring at some stage later then the "start" event, but because of problems/bugs/crashed with the data collector it could be that some are missing. In that case I would like to disregard the event without a "partner". That means that given the data: foo, 2010-06-10 19:45, start foo, 2010-06-10 19:47, start foo, 2010-06-10 20:13, stop ..I would like to just disregard the 19:45 start event and not just get two result rows both using the 20:13 stop event as the stop time. I've tried to join the table with itself in different ways, but the key problems for me seems to be to find a way to correctly identify the corresponding "stop" event to the "start" event for the given "name". The problem is exactly the same as you would have if you had table with employees stamping in and out of work and wanted to find out how much they actually were at work. I'm sure there must be well known solutions to this, but I can't seem to find them...

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• WCF - Return object without serializing?

  - by Mayo

  One of my WCF functions returns an object that has a member variable of a type from another library that is beyond my control. I cannot decorate that library's classes. In fact, I cannot even use DataContractSurrogate because the library's classes have private member variables that are essential to operation (i.e. if I return the object without those private member variables, the public properties throw exceptions). If I say that interoperability for this particular method is not needed (at least until the owners of this library can revise to make their objects serializable), is it possible for me to use WCF to return this object such that it can at least be consumed by a .NET client? How do I go about doing that? Update: I am adding pseudo code below... // My code, I have control [DataContract] public class MyObject { private TheirObject theirObject; [DataMember] public int SomeNumber { get { return theirObject.SomeNumber; } // public property exposed private set { } } } // Their code, I have no control public class TheirObject { private TheirOtherObject theirOtherObject; public int SomeNumber { get { return theirOtherObject.SomeOtherProperty; } set { // ... } } } I've tried adding DataMember to my instance of their object, making it public, using a DataContractSurrogate, and even manually streaming the object. In all cases, I get some error that eventually leads back to their object not being explicitly serializable.

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• PHP & MySQL username validation and storage problem.

  - by php

  For some reason when a user enters a brand new username the error message <p>Username unavailable</p> is displayed and the name is not stored. I was wondering if some can help find the flaw in my code so I can fix this error? Thanks Here is the PHP code. if($_POST['username'] && trim($_POST['username'])!=='') { $u = "SELECT * FROM users WHERE username = '$username' AND user_id <> '$user_id'"; $r = mysqli_query ($mysqli, $u) or trigger_error("Query: $u\n<br />MySQL Error: " . mysqli_error($mysqli)); if (mysqli_num_rows($r) == TRUE) { echo '<p>Username unavailable</p>'; $_POST['username'] = NULL; } else if(isset($_POST['username']) && mysqli_num_rows($r) == 0 && strlen($_POST['username']) <= 255) { $username = mysqli_real_escape_string($mysqli, $_POST['username']); } else if($_POST['username'] && strlen($_POST['username']) >= 256) { echo '<p>Username can not exceed 255 characters</p>'; } }

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• mysql - multiple where and search

  - by Shamil

  I'm trying to write a SQL query that satisfies multiple criteria. Of these, most are connected via a column, so joins are possible, however, some queries are such that I'd have to search additional tables for the information. What would be the least expensive and best way to do this? Let's say that we have a few tables. One table contains information such as sales information for a server: the salesperson, client id, service lease term, timestamps etc. It is possible that a client has multiple sales but with a different "service". I'd need to pick up all of the different ones. Another table has the quotes for the services, I'd need to pick some information out about this, whilst another, which could be joined to this one has some more information. Those tables are linked by a common client ID, so joins are possible, but I'd also need to search the first table for multiple instances of the client ID. Of course, I'd want to restrict the search to certain timestamps, which I can easily do as the timestamps are stored in MySQL format.

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• how to fetch data from Plist in Label

  - by SameSung Vs Iphone

  I have a RegistrationController screen to store email-id ,password,DOB,Height,Weight and logininController screen to match email-id and password to log-in purpose. Now In some third screen I have to fetch only the Height,Weight from the plist of the logged-in user to display it on the label.now if I Store the values of email-id and password in from LoginViewController in string and call it in the new screen to match if matches then gives Height,Weight ..if it corrects then how to fetch Height,Weight from the plist of the same one. how can i fetch from the stored plist in a string... the code which i used to match in LoginController -(NSArray*)readFromPlist { NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [documentPaths objectAtIndex:0]; NSString *documentPlistPath = [documentsDirectory stringByAppendingPathComponent:@"XYZ.plist"]; NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:documentPlistPath]; NSArray *valueArray = [dict objectForKey:@"title"]; return valueArray; } - (void)authenticateCredentials { NSMutableArray *plistArray = [NSMutableArray arrayWithArray:[self readFromPlist]]; for (int i = 0; i< [plistArray count]; i++) { id object = [plistArray objectAtIndex:i]; if ([object isKindOfClass:[NSDictionary class]]) { NSDictionary *objDict = (NSDictionary *)object; if ([[objDict objectForKey:@"pass"] isEqualToString:emailTextFeild.text] && [[objDict objectForKey:@"title"] isEqualToString:passwordTextFeild.text]) { NSLog(@"Correct credentials"); return; } NSLog(@"INCorrect credentials"); } else { NSLog(@"Error! Not a dictionary"); } } }

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• Calling function and running it

  - by devs

  I am quite new to objects and OOP. I really don't know how to explain it well but I'll try. So I am trying to read though JSON with JS, the JSON is passed from PHP. This would be easy if all of the information was on the same html page, but I' am trying something that I am new too. So let me show my code... First is the JS which is in app.js var Donors = function(){ var api = this.list; $(document).ready(function(){ $.getJSON(api, function(){ var donorObj = api.payload; $.each(donorObj, function(i, donor){ //console.log(donor.ign); }); }); }); } What I want this part to do is read from the JSON I'm giving it and console.log each name (or donor.ign) when the document is ready. On the html page, or header.php <script> $(function(){ var list = <?php cbProxy(); ?>; var Dons = new Donors(); Dons.list = list; }); </script> the data that's in list is the below JSON. You already know what the rest does, it just passes the JSON to the Donors() function. JSON example: { "code": 0, "payload": [ { "time": 1349661897, "packages": [ "49381" ], "ign": "Notch", "price": "15.99", "currency": "USD" } I'm use to just making functions and calling it on the same page or file and this is my first doing this kind of function. How can I get the function to run with the data I sent it so it console.log() each name.

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• What is the best way to implement a callback scenario using WCF and ASP.NET MVC?

  - by Mark Struzinski

  I am new to WCF. I just finished reading Learning WCF and I think I've got a pretty good grasp of the fundamentals. I am adding functionality to a line of business app that runs on ASP.NET MVC entirely inside the corporate LAN. I am calling into a service that will also send me events as they occur (and not as responses to service calls). These events can occur at any point during the user's session. I have the service written, and it is able to pick up these events. What would be the best way to deliver these events to the user? My initial thought is to run the WCF service in duplex mode over net TCP and implement the events as callbacks. Using this scenario, the best way I can think up to deliver the events to the user is a dictionary object stored in the session. The dictionary would be populated by the callbacks and polled on a set frequency for delivery via AJAX calls. Has anyone dealt with this scenario? Is there a more efficient way to implement this?

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• encrypting passwords in a python conf file on a windows platform

  - by Richard

  Hello all. I have a script running on a remote machine. db info is stored in a configuration file. I want to be able to encrypt the password in the conf text so that no one can just read the file and gain access to the database. This is my current set up: My conf file sensitive info is encoded with base64 module. The main script then decodes the info. I have compiled the script using py2exe to make it a bit harder to see the code. My question is: Is there a better way of doing this? I know that base64 is not a very safe way of encrypting. Is there a way to encode using a key? I also know that py2exe can be reversed engineered very easily and the key could be found. Any other thoughts? I am also running this script on a windows machine, so any modules that are suggested should be able to run in a windows environment with ease. I know there are several other posts on this topic but I have not found one with a windows solution, or at least one that is will explained.

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• Determining presence of prototype with correct return type

  - by R..

  Here's a random problem in C black magic I just came up with: Write a function that returns 1 if malloc has been prototyped to return a pointer type and 0 if malloc has a return type of int (either implicitly or due to wrong prototype), without invoking any implementation-defined or undefined behavior. I believe it's solvable, but I haven't worked out the solution. Note that calling the function cannot be necessary and in fact is not possible since calling a function with the incorrect prototype is undefined behavior. I have some ideas for ingredients but I think it makes for a better puzzle (and possibly more diverse ideas) if I leave them out for now. I don't need the solution for any immediate use, but it could be handy in configure scripts and such. Update: A better example of the usefulness (with strdup instead of malloc): #undef strdup #define strdup(x) (strdup_has_proto ? strdup((x)) : my_strdup((x))) i.e. being able to implement X_has_proto as an expression at the source level could be a portable way to use functions which a system might or might not have, and fall back on a local replacement, without needing any separate configure step.

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• Adding variably named fields to Python classes

  - by Carson Myers

  I have a python class, and I need to add an arbitrary number of arbitrarily long lists to it. The names of the lists I need to add are also arbitrary. For example, in PHP, I would do this: class MyClass { } $c = new MyClass(); $n = "hello" $c.$n = array(1, 2, 3); How do I do this in Python? I'm also wondering if this is a reasonable thing to do. The alternative would be to create a dict of lists in the class, but since the number and size of the lists is arbitrary, I was worried there might be a performance hit from this. If you are wondering what I'm trying to accomplish, I'm writing a super-lightweight script interpreter. The interpreter walks through a human-written list and creates some kind of byte-code. The byte-code of each function will be stored as a list named after the function in an "app" class. I'm curious to hear any other suggestions on how to do this as well.

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• choose javascript variable based on element id from jquery

  - by phoffer

  I feel like this is a simple question, but I am still relatively new to javascript and jquery. I am developing a site for a touch interface that uses unordered lists and jquery .click functions to take input data. I have a section to input a m:ss time, with 3 divs, each containing a list of digits for time. I need to get the input for each column and set it as a variable. I originally designed the inputs to change form inputs, because I didn't understand javascript very much. It was easy to change the 3 hidden inputs by using div id's, but I can't figure out how to do it now with javascript variables. Here is my original jquery code... $("div#time>div>ul>li").click(function() { var id = $(this).parents(".time").attr("name"); var number = $(this).html(); $("input#"+id).val(number); }); The last line sets one of 3 hidden inputs equal to whatever was clicked. I need to make it so separate variables take the inputs, then I can manipulate those variables however I want. Here's a short snippet of the html, to have an idea of how jquery grabs it. <div id="time"> <h1>Time</h1> <div name="minute" class="time" id="t_minute"> M : <ul> The full time html is here: link text Thanks everyone! I've been using SO to answer many questions I've had, but I couldn't find something for this, so I figured I would join, since I'm sure I will have more questions along the way.

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• c++ code cons/pros

  - by VirusEcks

  below i have a code that runs in most of my simple programs .. . i want to know if it's good/bad ... and cons/pros . . win32 header file: win32.h #include <windows.h> #include <process.h> #include <stdarg.h> main header file: inc.h #include "win32.h" #ifndef INCS #define INCS #define DD #else #define DD extern #endif #ifndef VARS #define titlen L"my program" #endif DD wchar_t gtitle[512]; DD wchar_t gclass[512]; DD wchar_t gdir[32767]; #include "resources.h" #include "commonfunctions.h" then all files have something like this commonfunctions.h DD inline bool icmp( const char *String1, const char *String2 ) { if ( _stricmp( String1, String2 ) == 0 ) { return true; } return false; } DD inline bool scmp( const char *String1, const char *String2 ) { if ( strcmp( String1, String2 ) == 0 ) { return true; } return false; } all global variables have DD infront of them and all functions have DD too . is there a bad side of this ? . i came up with this idea and it wasn't problematic at all in small programs . but before i apply it in a large project will it be problematic ?. thanks in advance.

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• How to properly cast a global memory array using the uint4 vector in CUDA to increase memory throughput?

  - by charis

  There are generally two techniques to increase the memory throughput of the global memory on a CUDA kernel; memory accesses coalescence and accessing words of at least 4 bytes. With the first technique accesses to the same memory segment by threads of the same half-warp are coalesced to fewer transactions while be accessing words of at least 4 bytes this memory segment is effectively increased from 32 bytes to 128. To access 16-byte instead of 1-byte words when there are unsigned chars stored in the global memory, the uint4 vector is commonly used by casting the memory array to uint4: uint4 *text4 = ( uint4 * ) d_text; var = text4[i]; In order to extract the 16 chars from var, i am currently using bitwise operations. For example: s_array[j * 16 + 0] = var.x & 0x000000FF; s_array[j * 16 + 1] = (var.x >> 8) & 0x000000FF; s_array[j * 16 + 2] = (var.x >> 16) & 0x000000FF; s_array[j * 16 + 3] = (var.x >> 24) & 0x000000FF; My question is, is it possible to recast var (or for that matter *text4) to unsigned char in order to avoid the additional overhead of the bitwise operations?

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• JQuery transition animation

  - by kk-dev11

  This program randomly selects two employees from a json-object Employees array, winnerPos is already defined. For better user experience I programmed these functions to change pictures one by one. The animation stops when the randomly selected person is shown on the screen. The slideThrough function will be triggered when the start button is pressed. function slideThrough() { counter = 0; start = true; clearInterval(picInterval); picInterval = setInterval(function () { changePicture(); }, 500); } function changePicture() { if (start) { if (counter > winnerPos) { setWinner(); start = false; killInterval(); } else { var employee = Employees[counter]; winnerPic.fadeOut(200, function () { this.src = 'img/' + employee.image; winnerName.html(employee.name); $(this).fadeIn(300); }); counter++; } } } The problem is the animation doesn't work smoothly. At first it works, but not perfect. The second time the transition happens in an irregular way, i.e. different speed and fadeIn/fadeOut differs from picture to picture. Could anyone help me to fine-tune the transition?

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• Output error in comparing characters from two strings

  - by Andrew Martin

  I'm stuck with my a piece of code I'm creating. My IDE is Eclipse and when I use its debugging feature, to trace what's happening on each line, it outputs perfectly. However, when I click the "run" project, it just outputs a blank screen: public static void compareInterests(Client[] clientDetails) { int interests = 0; for (int p = 0; p < numberOfClients; p++) { for (int q = 0; q < numberOfClients; q++) { String a = clientDetails[p].getClientInterests(); String b = clientDetails[q].getClientInterests(); int count = 0; while (count < a.length()) { if (a.charAt(count) == b.charAt(count)) interests++; count++; } if ((interests >= 3) && (clientDetails[p].getClientName() != clientDetails[q].getClientName())) System.out.print (clientDetails[p].getClientName() + " is compatible with " + clientDetails[q].getClientName()); interests = 0; } } } The code is designed to import an object array which contains information on a client's name and a client's interests. The client's interests are stored in the format "01010", where each 1 means they are interested in that activity, each 0 means they are not. My code compares each character of every client's string with every other client's string and outputs the results for all client's that don't have the same name and have three or more interests in common. When I run this code through Java's debugger, it outputs fine - but when I click run project or compile, I just get a blank screen. Any ideas?

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• And now for a complete change of direction from C++ function pointers

  - by David

  I am building a part of a simulator. We are building off of a legacy simulator, but going in different direction, incorporating live bits along side of the simulated bits. The piece I am working on has to, effectively route commands from the central controller to the various bits. In the legacy code, there is a const array populated with an enumerated type. A command comes in, it is looked up in the table, then shipped off to a switch statement keyed by the enumerated type. The type enumeration has a choice VALID_BUT_NOT_SIMULATED, which is effectively a no-op from the point of the sim. I need to turn those no-ops into commands to actual other things [new simulated bits| live bits]. The new stuff and the live stuff have different interfaces than the old stuff [which makes me laugh about the shill job that it took to make it all happen, but that is a topic for a different discussion]. I like the array because it is a very apt description of the live thing this chunk is simulating [latching circuits by row and column]. I thought that I would try to replace the enumerated types in the array with pointers to functions and call them directly. This would be in lieu of the lookup+switch.

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• (Python/Pyramid) Better ways to have standard list/form editors?

  - by badcat

  I'm working on a number of Pyramid (former Pylons) projects, and often I have the need to display a list of some content (let's say user accounts, log entries or simply some other data). A user should be able to paginate through the list, click on a row and get a form where he/she can edit the contents of that row. Right now I'm always re-inventing the wheel by having Mako templates which use webhelpers for the pagination, Jquery UI for providing a dialog and I craft the editor form and AJAX requests on the client and server side by hand. As you may know, this eats up painfully much time. So what I'm wondering is: Is there a better way of providing lists, editor dialog and server/client communication about this, without having to re-invent the wheel every time? I heard Django takes off a big load of that by providing user accounts and other stuff out of the box; but in my case it's not just about user accounts, it can be any kind of data that is stored on the server-side in a SQL database, which should be able to be edited by a user. Thanks in advance!

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• How To: Custom HTML / CSS Text Button for "Facebook like" & "Twitter Follow"

  - by 1Line

  So i have had a little hunt online about creating custom Facebook like buttons and custom twitter follow button but not really found a solution so thought i would ask here and see if anyone knows of a solution for this (currently i have coded some jQuery to get Facebook and Twitter counts using JSON which works but want some custom buttons as per below) I have the count working all ok, just need to tackle the like and follow buttons - it is done in jquery at the moment so would like to continue to use that if this has to be done via that. at the moment i use the API for each to get the count, if i can integrate into the current js i have to get the calls / functions i require would be good: // grab from facebook var facebook = $.getJSON('https://graph.facebook.com/'+f_page+'?callback=?', function(data) { fb_count = data['likes'].toString(); fb_count_gt = data['likes'].toString(); fb_count = add_commas(fb_count); $('#fb_count').html(fb_count); }); // grab from twitter var twitter = $.getJSON("https://twitter.com/users/"+t_page+".json?callback=?",function(data) { twit_count = data['followers_count'].toString(); twit_count_gt = data['followers_count'].toString(); twit_count = add_commas(twit_count); $('#twitter_count').html(twit_count); }); Thanks in advance!

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• How do I simplify my code?

  - by Mitchell Skurnik

  I just finished creating my first major application in C#/Silverlight. In the end the total line count came out to over 12,000 lines of code. Considering this was a rewrite of a php/javascript application I created 2 years that was over 28,000 lines I am actually quite proud of my accomplishment. After reading many questions and answers here on stackoverflow and other sites online, I followed many posters advice: I created classes, procedures, and such for things that I would have a year ago copied and pasted; I created logic charts to figure out complex functions; making sure there are no crazy hidden characters (used tabs instead of spaces); and a few others things; place comments where necessary (I have lots of comments). My application consists of 4 tiles laid out horizontally that have user controls loaded into each slice. You can have between one and four slices loaded at anytime. If you have once slice loaded, the slice takes up the entire artboard...if you have 2 loaded, each take up half, 3 a third, 4 a quarter. Each one of these slices represent (for the sake of this example) a light control. Each slice has 3 slider controls in it. Now when I coded the functionality of the sliders, I used a switch/case statement inside of a public function that would run the command on the specified slice/slider. The made for some duplicate code but I saw no way around it as each slice was named differently. So I would do slice1.my.commands(); slice2.my.commands(); etc. My question to you is how do I clean up my code even futher? (Sadly I cannot post any of my code). Is there any way to take this repetion out of my code?

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• Cancel text selection on textinput in Flex

  - by Michael

  So the real problem is the lack of an onReleaseOutside function. I found some examples of how to bypass this during a drag function but it was not applicable for a text input. The problem is that when a user selects some text in textinput and mouses off the application area and then mouses up, I'm getting a problem that the textinput keeps thinking that the mouse down is actively selecting text in the textinput and continually overwrites the characters being entered in the textinput. You can test this at http://palermo.infusedindustries.com [ in the search bar of the live store on the page, type some text, then highlight it all and don't let up on the mouse until you are outside the store. I finally hacked some junk together so I can tell if the mouse goes off the stage using some code like var x = stage.mouseX; var y = stage.mouseY; if(x < 0 || y <0 || x >stage.stageWidth || y > stage.stageHeight) I'd like to just make the textinput stop thinking it should be highlighting text so that even if the user scrolls out of the applet and mouses up that the text input still overwrites what is in the search bar and functions as normal. I can't seem to find any events or ways to tell the Flex text field to stop thinking that the mouse is down and that the user is done selecting text.

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• Trouble using files Globally

  - by Nightforce2

  Recently I ran into trouble when I discovered that vista restricts what can be installed into the system32 directory even though I am the administrator for this computer. It will not allow me to register dll files so I can use programs like wget globally like how programs "nslookup" etc are used. Keeps giving me this error. Regsvr32: The module "C:\Windows\System32\libeay32.dll" failed to load. make sure the binary is stored at the specified path or debug it to check for problems with the binary or dependent .DLL files. The specified module could not be found. Moving the required DLL files to system32 prompts me to confirm administrator privileges are needed to move these files, So I give the permission, copy the files to system32, and run wget to confirm. This is where it tells me it cannot find the DLL's required to run and when using regsvr32 it says it cannot find the entry point so it will not load the DLL asking me if it is a valid DLL or OCX file. If I leave the DLL's that came with wget in the same folder as wget outsite of system32 they work vice adding them to system32 with the exe it will not work saying it cannot read the those dll files. Is there a way around this or Do I need to Upgrade to Windows 7 to get away from these problems/restrictions?

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• Embedded Youtube video in a Ruby on Rails page

  - by dan

  Hi, New to programming. I am trying to embed a YouTube video from a link stored in a database named "Promoter" into a ruby-on-rails page (.erb). I've looked at the source the code turns out, but the object video player does not appear (on heroku here: http://blazing-mountain-574.heroku.com/). The code in the home.html.erb file: <h1>Pages#home</h1> <p>Find me in app/views/pages/home.html.erb</p> <object width="640" height="385"> <param name="movie" value="<%= sanitize Promoter.first.link %>"> </param><param name="allowFullScreen" value="true"></param ><param name="allowscriptaccess" value="always"></param> <embed src="<%= sanitize Promoter.first.link %>" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object> Is there something real simple that I'm missing?

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• Subversion (svn) beginner's questions

  - by Marius

  Hello, Here's what i'm trying to do. I have a project in /var/www/project. I'd like to use svn for this project. I've installed SVN on my debian server for this purpose, but i don't understand how to use it and the googling got me even more confused. I'd like to create a repository /var/svn/project and use it. After some changes occur, i'd like to export all the code back to /var/www/project. Now here's what i've done: i've created a repository: svnadmin create /var/svn/project i've imported the code: svn import /var/www/project file:///var/svn/project -m "Initial import" i've checked out the code with "Versions" client Everything seems to work fine, but ... If i go to /var/svn/project, there are no source files from my project there or in any subdirectory. Although the svn client is able to checkout all of those files. So i've read that in svn, files are not stored separately neither in berkley db nor in fsfs filesystems. Then the question is ... how do i export the source back to /var/www/project? If i do an svn export command on the /var/svn/project directory, it says i'm not in a working copy :(

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• Holding variables in memory, C++

  - by b-gen-jack-o-neill

  Today something strange came to my mind. When I want to hold some string in C (C++) the old way, without using string header, I just create array and store that string into it. But, I read that any variable definition in C in local scope of function ends up in pushing these values onto the stack. So, the string is actually 2* bigger than needed. Because first, the push instructions are located in memory, but then when they are executed (pushed onto the stack) another "copy" of the string is created. First the push instructions, than the stack space is used for one string. So, why is it this way? Why doesn't compiler just add the string (or other variables) to the program instead of creating them once again when executed? Yes, I know you cannot just have some data inside program block, but it could just be attached to the end of the program, with some jump instruction before. And than, we would just point to these data? Because they are stored in RAM when the program is executed. Thanks.

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• Does std::vector change its address? How to avoid

  - by kunigami

  Since vector elements are stored contiguously, I guess it may not have the same address after some push_back's , because the initial allocated space could not suffice. I'm working on a code where I need a reference to an element in a vector, like: int main(){ vector<int> v; v.push_back(1); int *ptr = &v[0]; for(int i=2; i<100; i++) v.push_back(i); cout << *ptr << endl; //? return 0; } But it's not necessarily true that ptr contains a reference to v[0], right? How would be a good way to guarantee it? My first idea would be to use a vector of pointers and dynamic allocation. I'm wondering if there's an easier way to do that? PS.: Actually I'm using a vector of a class instead of int, but I think the issues are the same.

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