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• Need some help deciphering a line of assembler code, from .NET JITted code

  - by Lasse V. Karlsen

  In a C# constructor, that ends up with a call to this(...), the actual call gets translated to this: 0000003d call dword ptr ds:[199B88E8h] What is the DS register contents here? I know it's the data-segment, but is this call through a VMT-table or similar? I doubt it though, since this(...) wouldn't be a call to a virtual method, just another constructor. I ask because the value at that location seems to be bad in some way, if I hit F11, trace into (Visual Studio 2008), on that call-instruction, the program crashes with an access violation. The code is deep inside a 3rd party control library, where, though I have the source code, I don't have the assemblies compiled with enough debug information that I can trace it through C# code, only through the disassembler, and then I have to match that back to the actual code. The C# code in question is this: public AxisRangeData(AxisRange range) : this(range, range.Axis) { } Reflector shows me this IL code: .maxstack 8 L_0000: ldarg.0 L_0001: ldarg.1 L_0002: ldarg.1 L_0003: callvirt instance class DevExpress.XtraCharts.AxisBase DevExpress.XtraCharts.AxisRange::get_Axis() L_0008: call instance void DevExpress.XtraCharts.Native.AxisRangeData::.ctor(class DevExpress.XtraCharts.ChartElement, class DevExpress.XtraCharts.AxisBase) L_000d: ret It's that last call there, to the other constructor of the same class, that fails. The debugger never surfaces inside the other method, it just crashes. The disassembly for the method after JITting is this: 00000000 push ebp 00000001 mov ebp,esp 00000003 sub esp,14h 00000006 mov dword ptr [ebp-4],ecx 00000009 mov dword ptr [ebp-8],edx 0000000c cmp dword ptr ds:[18890E24h],0 00000013 je 0000001A 00000015 call 61843511 0000001a mov eax,dword ptr [ebp-4] 0000001d mov dword ptr [ebp-0Ch],eax 00000020 mov eax,dword ptr [ebp-8] 00000023 mov dword ptr [ebp-10h],eax 00000026 mov ecx,dword ptr [ebp-8] 00000029 cmp dword ptr [ecx],ecx 0000002b call dword ptr ds:[1889D0DCh] // range.Axis 00000031 mov dword ptr [ebp-14h],eax 00000034 push dword ptr [ebp-14h] 00000037 mov edx,dword ptr [ebp-10h] 0000003a mov ecx,dword ptr [ebp-0Ch] 0000003d call dword ptr ds:[199B88E8h] // this(range, range.Axis)? 00000043 nop 00000044 mov esp,ebp 00000046 pop ebp 00000047 ret Basically what I'm asking is this: What the purpose of the ds:[ADDR] indirection here? VMT-table is only for virtual isn't it? and this is constructor Could the constructor have yet to be JITted, which could mean that the call would actually call through a JIT shim? I'm afraid I'm in deep water here, so anything might and could help. Edit: Well, the problem just got worse, or better, or whatever. We are developing the .NET feature in a C# project in a Visual Studio 2008 solution, and debugging and developing through Visual Studio. However, in the end, this code will be loaded into a .NET runtime hosted by a Win32 Delphi application. In order to facilitate easy experimentation of such features, we can also configure the Visual Studio project/solution/debugger to copy the produced dll's to the Delphi app's directory, and then execute the Delphi app, through the Visual Studio debugger. Turns out, the problem goes away if I run the program outside of the debugger, but during debugging, it crops up, every time. Not sure that helps, but since the code isn't slated for production release for another 6 months or so, then it takes some of the pressure off of it for the test release that we have soon. I'll dive into the memory parts later, but probably not until over the weekend, and post a followup.

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• Chord Chart - Skip to key with a click

  - by Juan Gonzales

  I have a chord chart app that basically can transpose a chord chart up and down throughout the keys, but now I would like to expand that app and allow someone to pick a key and automatically go to that key upon a click event using a function in javascript or jquery. Can someone help me figure this out? The logic seems simple enough, but I'm just not sure how to implement it. Here are my current functions that allow the user to transpose up and down... var match; var chords = ['C','C#','D','D#','E','F','F#','G','G#','A','A#','B','C','Db','D','Eb','E','F','Gb','G','Ab','A','Bb','B','C']; var chords2 = ['C','Db','D','Eb','E','F','Gb','G','Ab','A','Bb','B','C','C#','D','D#','E','F','F#','G','G#','A','A#','C']; var chordRegex = /(?:C#|D#|F#|G#|A#|Db|Eb|Gb|Ab|Bb|C|D|E|F|G|A|B)/g; function transposeUp(x) { $('.chord'+x).each(function(){ ///// initializes variables ///// var currentChord = $(this).text(); // gatheres each object var output = ""; var parts = currentChord.split(chordRegex); var index = 0; ///////////////////////////////// while (match = chordRegex.exec(currentChord)){ var chordIndex = chords2.indexOf(match[0]); output += parts[index++] + chords[chordIndex+1]; } output += parts[index]; $(this).text(output); }); } function transposeDown(x){ $('.chord'+x).each(function(){ var currentChord = $(this).text(); // gatheres each object var output = ""; var parts = currentChord.split(chordRegex); var index = 0; while (match = chordRegex.exec(currentChord)){ var chordIndex = chords2.indexOf(match[0],1); //var chordIndex = $.inArray(match[0], chords, -1); output += parts[index++] + chords2[chordIndex-1]; } output += parts[index]; $(this).text(output); }); } Any help is appreciated. Answer will be accepted! Thank You

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• How to get debugging of an App Engine application working?

  - by Chris Lacy

  I've got 10+ years in C/C++, and it appears Visual Studio has spoilt me during that time. In Visual Studio, debbuging issimple: I just add a breakpoint to a line of code, and as soon as that code is executed, my breakpoint triggers, at which point I can view a callstack, local/member variables, etc. I'm trying to achieve this functionality under App Engine. I assume that is possible? All the searching I've done to this point has led me to using Pydev in Eclipse. As best I can tell, I am successfully launching my simple 'hello world' program in Debug mode. But the IDE doesn't even seem to have an option to set a breakpoint? I must be missing something. I've googled long and hard about this, but am having no luck. Most results trace back to the same old threads that don't deal directly with my issue. Can anyone shed some light on how you get basic debugging setup using Pydev/Eclipse with App Engine? Alternatively, if there's an easier way to debug App Engine than using Pydev/Eclipse, I'd love to hear about it. Thanks in advance.

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• Array Recursion

  - by GeeYouAreYou

  I've got an assignment I can't figure out, any pointers will be much appreciated, it goes like so: There's a series of light bulbs represented as an array of true/false, there's a switch for every light bulb, by clicking it for any light bulb, you toggle it as well as 2 adjacent ones (1 from left & another 1 from right; if clicked switch's bulb on edge -- only 1 adjacent toggled of course). What is needed to accomplish is a method that accepts an array of a series of turned on/off light bulbs and another one representing another state of supposedly the 1st array after some switches have been clicked..! So recursion must be used to find out whether there's a combination of switch clicks that will transform array 1 to array 2. Here's the signature of the method: public static boolean disco(boolean[] init, boolean[] target) Will return true if array init can be transformed to target, false otherwise. Method must be static and not use any other static and global variables, only local. Example: boolean[] init = {true, false, true, false, true, false}; boolean[] target = {false, true, false, true, false, true}; For above 2 arrays, disco(init, target) will return true because toggling the 1st and 4th bulbs would yield the target state (remember adjacent bulbs being toggled as well). Any help much appreciated..!!

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• PHP: How to store XML data in an array?

  - by tommy

  Below is the XML I am working with - there are more items - this is the first set. How can I get these elements in to an array? I have been trying with PHP's SimpleXML etc. but I just cant do it. <response xmlns:lf="http://api.lemonfree.com/ns/1.0"> <lf:request_type>listing</lf:request_type> <lf:response_code>0</lf:response_code> <lf:result type="listing" count="10"> <lf:item id="56832429"> <lf:attr name="title">Used 2005 Ford Mustang V6 Deluxe</lf:attr> <lf:attr name="year">2005</lf:attr> <lf:attr name="make">FORD</lf:attr> <lf:attr name="model">MUSTANG</lf:attr> <lf:attr name="vin">1ZVFT80N555169501</lf:attr> <lf:attr name="price">12987</lf:attr> <lf:attr name="mileage">42242</lf:attr> <lf:attr name="auction">no</lf:attr> <lf:attr name="city">Grand Rapids</lf:attr> <lf:attr name="state">Michigan</lf:attr> <lf:attr name="image">http://www.lemonfree.com/images/stock_images/thumbnails/2005_38_557_80.jpg</lf:attr> <lf:attr name="link">http://www.lemonfree.com/56832429.html</lf:attr> </lf:item> <!-- more items --> </lf:result> </response> Thanks guys EDIT: I want the first items data in easy to access variables, I've been struggling for a couple of days to get SimpleXML to work as I am new to PHP, so I thought manipulating an array is easier to do.

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• Are Parameters really enough to prevent Sql injections?

  - by Rune Grimstad

  I've been preaching both to my colleagues and here on SO about the goodness of using parameters in SQL queries, especially in .NET applications. I've even gone so far as to promise them as giving immunity against SQL injection attacks. But I'm starting to wonder if this really is true. Are there any known SQL injection attacks that will be successfull against a parameterized query? Can you for example send a string that causes a buffer overflow on the server? There are of course other considerations to make to ensure that a web application is safe (like sanitizing user input and all that stuff) but now I am thinking of SQL injections. I'm especially interested in attacks against MsSQL 2005 and 2008 since they are my primary databases, but all databases are interesting. Edit: To clarify what I mean by parameters and parameterized queries. By using parameters I mean using "variables" instead of building the sql query in a string. So instead of doing this: SELECT * FROM Table WHERE Name = 'a name' We do this: SELECT * FROM Table WHERE Name = @Name and then set the value of the @Name parameter on the query / command object.

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• PHP $_SERVER['HTTP_HOST'] vs. $_SERVER['SERVER_NAME'], am I understanding the man pages correctly?

  - by Jeff

  I did a lot of searching and also read the PHP $_SERVER man page. Do I have this right regarding which to use for my PHP scripts for simple link definitions used throughout my site? $_SERVER['SERVER_NAME'] is based on your web servers' config file (Apache2 in my case), and varies depending on a few directives: (1) VirtualHost, (2) ServerName, (3) UseCanonicalName, etc. $_SERVER['HTTP_HOST'] is based on the request from the client. Therefore, it would seem to me that the proper one to use in order to make my scripts as compatible as possible would be $_SERVER['HTTP_HOST']. Is this assumption correct? Followup comments: I guess I got a little paranoid after reading this article and noting that someone said "they wouldn't trust any of the $_SERVER vars": http://markjaquith.wordpress.com/2009/09/21/php-server-vars-not-safe-in-forms-or-links/ and also: http://www.php.net/manual/en/reserved.variables.server.php (comment: Vladimir Kornea 14-Mar-2009 01:06) Apparently the discussion is mainly about $_SERVER['PHP_SELF'] and why you shouldn't use it in the form action attribute without proper escaping to prevent XSS attacks. My conclusion about my original question above is that it is "safe" to use $_SERVER['HTTP_HOST'] for all links on a site without having to worry about XSS attacks, even when used in forms. Please correct me if I'm wrong.

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• How do I repass a function pointer in C++

  - by fneep

  Firstly, I am very new to function pointers and their horrible syntax so play nice. I am writing a method to filter all pixels in my bitmap based on a function that I pass in. I have written the method to dereference it and call it in the pixel buffer but I also need a wrapper method in my bitmap class that takes the function pointer and passes it on. How do I do it? What is the syntax? I'm a little stumped. Here is my code with all the irrelevant bits stripped out and files combined (read all variables initialized filled etc.). struct sColour { unsigned char r, g, b, a; }; class cPixelBuffer { private: sColour* _pixels; int _width; int _height; int _buffersize; public: void FilterAll(sColour (*FilterFunc)(sColour)); }; void cPixelBuffer::FilterAll(sColour (*FilterFunc)(sColour)) { // fast fast fast hacky FAST for (int i = 0; i < _buffersize; i++) { _pixels[i] = (*FilterFunc)(_pixels[i]); } } class cBitmap { private: cPixelBuffer* _pixels; public: inline void cBitmap::Filter(sColour (*FilterFunc)(sColour)) { //HERE!! } };

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• PHP str_replace and preg_replace work on one server but not another

  - by retailevolved

  I have a simple function on a php page that takes a url such as: http://myurl.com/mypage.html?param1=value1 and converts it to: http://myurl.com/searchpage.html?param1=value1 All it does it swap out the page.html portion. To do this, I use the following: $currentUrl = $this-getCurrentUrl(); // Grabs the current url, i.e 'http://myurl.com/mypage.html?param1=value1' // Derive a search pattern from the current url $pattern = "/" . str_replace(array("/", ".", "-"), array("\\/", "\\.", "\\-"), $currentUrl) . "/"; // get rid of the 'mypage.html' $newUrl = preg_replace($pattern, 'http://myurl.com/', $currentUrl); // replace the question mark with the correct page $newUrl = str_replace("/?", "/searchpage.html?", $newUrl); The above code is not the exact code but is a good representation. It works beautifully on one server, but when I push to production, the preg_replace does not work. I originally attempted to use str_replace. It also works on my local development machine, but not on the production server. I have confirmed that the URL variables are coming in correctly. Any ideas?

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• NSPredicate as a constraint solver?

  - by Felixyz

  I'm working on a project which includes some slightly more complex dynamic layout of interface elements than what I'm used to. I always feel stupid writing complex code that checks if so-and-so is close to such-and-such and in that case move it x% in some direction, etc. That's just not how programming should be done. Programming should be as declarative as possible! Precisely because what I'm going to do is fairly simple, I thought it would be a good opportunity to try something new, and I thought of using NSPredicate as a simple constraints solver. I've only used NSPredicate for very simple tasks so far, but I know that it capable of much more. Are there any ideas, experiences, examples, warnings, insights that could be useful here? I'll give a very simple example so there will be something concrete to answer. How could I use NSPredicate to solve the following constraints: viewB.xmid = (viewB.leftEdge + viewB.width) / 2 viewB.xmid = max(300, viewA.rightEdge + 20 + viewB.width/2) ("viewB should be horizontally centered on coordinate 300, unless its left edge gets within 20 pixels of viewB's right edge, in which case viewA's left edge should stay fixed at 20 pixels to the right of viewB's right edge and viewA's horizontal center get pushed to the right.") viewA.rightEdge and viewB.width can vary, and those are the 'input variables'. EDIT: Any solution would probably have to use the NSExpression method -(id)expressionValueWithObject:(id)object context:(NSMutableDictionary *)context. This answer is relevant.

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• Can ElementTree be told to preserve the order of attributes?

  - by dmckee

  I've written a fairly simple filter in python using ElementTree to munge the contexts of some xml files. And it works, more or less. But it reorders the attributes of various tags, and I'd like it to not do that. Does anyone know a switch I can throw to make it keep them in specified order? Context for this I'm working with and on a particle physics tool that has a complex, but oddly limited configuration system based on xml files. Among the many things setup that way are the paths to various static data files. These paths are hardcoded into the existing xml and there are no facilities for setting or varying them based on environment variables, and in our local installation they are necessarily in a different place. This isn't a disaster because the combined source- and build-control tool we're using allows us to shadow certain files with local copies. But even thought the data fields are static the xml isn't, so I've written a script for fixing the paths, but with the attribute rearrangement diffs between the local and master versions are harder to read than necessary. This is my first time taking ElementTree for a spin (and only my fifth or sixth python project) so maybe I'm just doing it wrong. Abstracted for simplicity the code looks like this: tree = elementtree.ElementTree.parse(inputfile) i = tree.getiterator() for e in i: e.text = filter(e.text) tree.write(outputfile) Reasonable or dumb? Related links: How can I get the order of an element attribute list using Python xml.sax? Preserve order of attributes when modifying with minidom

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• Pass ng-model and place-holder value into directive

  - by Zen

  I have a segment of code needs to be reuse a lot, there for I want to just create a directive for it. <div class="btn-group"> <div class="input-group"> <div class="has-feedback"> <input type="text" class="form-control" placeholder="BLAH BLAH" ng-model="model"> <span class="times form-control-feedback" ng-click="model=''" ng-show="model.length > 0"></span> </div> </div> </div> I want to use this code as template in directive. Create a directive used as follow: <div search-Field ng-model="model" placeholder="STRING"></div> to replace to old html, ng-model and placeholder will be as variables. angular.module('searchField', []) .directive('searchField', [function () { return { scope: { placeholder: '@', ngModel: '=' }, templateUrl: 'Partials/_SearchInputGroup.html' } }]); Is it the way of doing it?

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• Calling PHP functions within HEREDOC strings

  - by Doug Kavendek

  In PHP, the HEREDOC string declarations are really useful for outputting a block of html. You can have it parse in variables just by prefixing them with $, but for more complicated syntax (like $var[2][3]), you have to put your expression inside {} braces. In PHP 5, it is possible to actually make function calls within {} braces inside a HEREDOC string, but you have to go through a bit of work. The function name itself has to be stored in a variable, and you have to call it like it is a dynamically-named function. For example: $fn = 'testfunction'; function testfunction() { return 'ok'; } $string = <<< heredoc plain text and now a function: {$fn()} heredoc; As you can see, this is a bit more messy than just: $string = <<< heredoc plain text and now a function: {testfunction()} heredoc; There are other ways besides the first code example, such as breaking out of the HEREDOC to call the function, or reversing the issue and doing something like: ?> <!-- directly outputting html and only breaking into php for the function --> plain text and now a function: <?PHP print testfunction(); ?> The latter has the disadvantage that the output is directly put into the output stream (unless I'm using output buffering), which might not be what I want. So, the essence of my question is: is there a more elegant way to approach this? Edit based on responses: It certainly does seem like some kind of template engine would make my life much easier, but it would require me basically invert my usual PHP style. Not that that's a bad thing, but it explains my inertia.. I'm up for figuring out ways to make life easier though, so I'm looking into templates now.

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• AJAX Submit to PHP still loading page after preventDefault()

  - by dannyburrows

  I have a webpage that I am using .ajax to send variables to a php script. The php page is loading into the browser as if I was navigating to it. The script is loading the data correctly, so my issue is stopping the navigation and keeping the user on the original page. The code for my form is here: echo "<form method='post' action='addTask.php' id='myform'>\n"; echo "<input name='addtask' id='addtask' maxlength='64'/><br/>\n"; echo "<input type='submit' name='submit' id='submit' value='Add Task'/>\n"; echo "</form>\n"; The code for my jquery is here: $(function(){ $('#myform').submit(function(e){ e.stopPropagation(); $.ajax({ url: 'addTask.php', type: 'POST', data: {}, success: alert("Success") }); }); }); I have tried: e.preventDefault(), e.stopPropagation() and return false. Any help is appreciated. $("#submit").click(function(e){ e.preventDefault(); $.ajax({ type: "POST", url: "addtask.php", data: { } }) .done(function() { alert( "success" ); }) .fail(function() { alert( "error" ); }); and $(function(){ $('#myform').submit(function(e){ e.preventDefault(); $.ajax({ url: 'addTask.php', type: 'POST', data: {}, success: function(){alert("Success")} }); }); });

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• How to allow users to define financial formulas in a C# app

  - by Peter Morris

  I need to allow my users to be able to define formulas which will calculate values based on data. For example //Example 1 return GetMonetaryAmountFromDatabase("Amount due") * 1.2; //Example 2 return GetMonetaryAmountFromDatabase("Amount due") * GetFactorFromDatabase("Discount"); I will need to allow / * + - operations, also to assign local variables and execute IF statements, like so var amountDue = GetMonetaryAmountFromDatabase("Amount due"); if (amountDue > 100000) return amountDue * 0.75; if (amountDue > 50000) return amountDue * 0.9; return amountDue; The scenario is complicated because I have the following structure.. Customer (a few hundred) Configuration (about 10 per customer) Item (about 10,000 per customer configuration) So I will perform a 3 level loop. At each "Configuration" level I will start a DB transaction and compile the forumlas, each "Item" will use the same transaction + compiled formulas (there are about 20 formulas per configuration, each item will use all of them). This further complicates things because I can't just use the compiler services as it would result in continued memory usage growth. I can't use a new AppDomain per each "Configuration" loop level because some of the references I need to pass cannot be marshalled. Any suggestions?

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• How to make a big switch control structure with variable check values?

  - by mystify

  For example, I have a huge switch control structure with a few hundred checks. They're an animation sequence, which is numbered from 0 to n. Someone said I can't use variables with switch. What I need is something like: NSInteger step = 0; NSInteger i = 0; switch (step) { case i++: // do stuff break; case i++: // do stuff break; case i++: // do stuff break; case i++: // do stuff break; } The point of this is, that the animation system calls a method with this big switch structure, giving it a step number. I want to be able to simply cut-copy-paste large blocks and put them in a different position inside the switch. for example, the first 50 blocks to the end. I could do that easily with a huge if-else structure, but it would look ugly and something tells me switch is much faster. How to?

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• How to prevent parallel builds per build configuration across multiple Build Agents

  - by vanslly

  I have many build configurations in TeamCity, each servicing a large project. In the past if a build is kicked off the Build Agent could be busy for up to 20min! In order to improve throughput I installed a second Build Agent on the same machine such that if a build run is kicked off by say Build Agent 1 and it is busy for 20min and someone from another project makes a change then Build Agent 2 can do the build for the other project without needing to wait on the current build run to finish. All was well until two successive check-ins resulted in both Build Agents running a build for a single build configuration in parallel. Since some resources are shared, IIS directories & databases, I don't want a single build configuration to run on both Build Agents in parallel. How can I ensure a build isn't triggered if a build is currently running for that build configuration on a different build agent? One way seems to involve environmental variables and ensuring a 50/50 split by Build Agent in terms of build configuration compatibility, but that seems a little clunky.

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• Whats wrong with my cookies?

  - by William

  For some reason This php script won't echo my cookie variable: <?php require 'connection.php'; require 'variables.php'; $name = $_POST['name']; $pass = $_POST['pass']; if(($name == $admin_name) && ($pass == $admin_pass)){ setcookie($forum_url."name",$name,time()+604800); setcookie($forum_url."pass",$pass,time()+604800); } else echo 'Failed'; ?> heres the html that gets sent to admin_login.php <form method=post action=admin_login.php> <div id="formdiv"> <div class="fieldtext1">Name</div> <div class="fieldtext1">Pass</div> <input type="text" name=name size=25 /> <input type="password" name=pass size=25 /> </div> <input type=submit value="Submit" id="submitbutton"> </form> here is the index, where I want the info echoed <?php echo $_COOKIE[$forum_url."name"]; ?> What am I doing wrong?

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• How to override the default init.tcl

  - by Sean Murphy

  I'm working on a project where I want to make use of TCL as the command interpreter. I have a working c library object which I can load from within the tcl shell but my problem is finding a way to automatically do this while starting a tclsh. Essentially my ultimate goal is to be able to run a script and have it load my library and run some initial startup tcl code before dropping me back to the tclsh command prompt in interactive mode. e.g. tclsh -f myscript.tcl --then-switch-to-interactive or EXPORT TCLINIT=myscript.tcl tclsh The basic goal is to avoid having to distribute tclsh but rather rely in local user installations of tcl. All I would like to distribute is my library, a startup script and a shell command to launch the tclsh with the library preloaded. I've tried using the environment variables TCLINIT and TCL_LIBRARY but they seem to have no effect. The only workable solutions I've found so far are to add "source myscript.tcl" to either the end of /usr/share/tcltk/tcl8.5.init.tcl or ~/.tclshrc However both of these "solutions" are non perfect as they require modification of the default users workspace. It strikes me that there must be a way to handle this in TCL, but my research so far hasn't yielded anything. Does anyone have any suggestions?

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• LINQDataSource and private columns

  - by fyjham

  Hey, I was trying to use a ListView bound to a LinqDataSource to insert to a table where I had a few columns private to the table class (Specifically password columns - only access I want to give outside the class is methods that generate the salt and encrypt the password to store it in 1 go). I gave this a few shots, but I didn't come up with anything I really liked... was wondering if anyone has a better way to do this. The methods I've found: Use the LinqDataSource inserting event and make the appropriate calls on e.NewObject. I don't really like this because it's so far removed from the actual input and there's no simple way to hold the password in the meantime other than a class variable set during the ListView's inserting event (Which works, but seems a little dodgy). Open up these properties and just ask everyone to use the appropriate static methods for encoding the passwords they pass in. I don't really like this cause I'd prefer that class to enforce data integrity rather than relying on all calling code doing it properly... I'm currently going with option #1, but I don't really like passing values between events using class variables like that (It just seems unstructured... even though I can guarantee the events will happen in the right order). Does anyone know a better way, or alternatively am I being too pedantic and one of the methods above is actually the right way to go? Thanks

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• Computing complex math equations in python

  - by dassouki

  Are there any libraries or techniques that simplify computing equations ? Take the following two examples: F = B * { [ a * b * sumOf (A / B ''' for all i ''' ) ] / [ sumOf(c * d * j) ] } where: F = cost from i to j B, a, b, c, d, j are all vectors in the format [ [zone_i, zone_j, cost_of_i_to_j], [..]] This should produce a vector F [ [1,2, F_1_2], ..., [i,j, F_i_j] ] T_ij = [ P_i * A_i * F_i_j] / [ SumOf [ Aj * F_i_j ] // j = 1 to j = n ] where: n is the number of zones T = vector [ [1, 2, A_1_2, P_1_2], ..., [i, j, A_i_j, P_i_j] ] F = vector [1, 2, F_1_2], ..., [i, j, F_i_j] so P_i would be the sum of all P_i_j for all j and Aj would be sum of all P_j for all i I'm not sure what I'm looking for, but perhaps a parser for these equations or methods to deal with multiple multiplications and products between vectors? To calculate some of the factors, for example A_j, this is what i use from collections import defaultdict A_j_dict = defaultdict(float) for A_item in TG: A_j_dict[A_item[1]] += A_item[3] Although this works fine, I really feel that it is a brute force / hacking method and unmaintainable in the case we want to add more variables or parameters. Are there any math equation parsers you'd recommend? Side Note: These equations are used to model travel. Currently I use excel to solve a lot of these equations; and I find that process to be daunting. I'd rather move to python where it pulls the data directly from our database (postgres) and outputs the results into the database. All that is figured out. I'm just struggling with evaluating the equations themselves. Thanks :)

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• How can I create a new Person object correctly in Javascript?

  - by TimDog

  I'm still struggling with this concept. I have two different Person objects, very simply: ;Person1 = (function() { function P (fname, lname) { P.FirstName = fname; P.LastName = lname; return P; } P.FirstName = ''; P.LastName = ''; var prName = 'private'; P.showPrivate = function() { alert(prName); }; return P; })(); ;Person2 = (function() { var prName = 'private'; this.FirstName = ''; this.LastName = ''; this.showPrivate = function() { alert(prName); }; return function(fname, lname) { this.FirstName = fname; this.LastName = lname; } })(); And let's say I invoke them like this: var s = new Array(); //Person1 s.push(new Person1("sal", "smith")); s.push(new Person1("bill", "wonk")); alert(s[0].FirstName); alert(s[1].FirstName); s[1].showPrivate(); //Person2 s.push(new Person2("sal", "smith")); s.push(new Person2("bill", "wonk")); alert(s[2].FirstName); alert(s[3].FirstName); s[3].showPrivate(); The Person1 set alerts "bill" twice, then alerts "private" once -- so it recognizes the showPrivate function, but the local FirstName variable gets overwritten. The second Person2 set alerts "sal", then "bill", but it fails when the showPrivate function is called. The new keyword here works as I'd expect, but showPrivate (which I thought was a publicly exposed function within the closure) is apparently not public. I want to get my object to have distinct copies of all local variables and also expose public methods -- I've been studying closures quite a bit, but I'm still confused on this one. Thanks for your help.

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• Please help us non-C++ developers understand what RAII is

  - by Charlie Flowers

  Another question I thought for sure would have been asked before, but I don't see it in the "Related Questions" list. Could you C++ developers please give us a good description of what RAII is, why it is important, and whether or not it might have any relevance to other languages? I do know a little bit. I believe it stands for "Resource Acquisition is Initialization". However, that name doesn't jive with my (possibly incorrect) understanding of what RAII is: I get the impression that RAII is a way of initializing objects on the stack such that, when those variables go out of scope, the destructors will automatically be called causing the resources to be cleaned up. So why isn't that called "using the stack to trigger cleanup" (UTSTTC:)? How do you get from there to "RAII"? And how can you make something on the stack that will cause the cleanup of something that lives on the heap? Also, are there cases where you can't use RAII? Do you ever find yourself wishing for garbage collection? At least a garbage collector you could use for some objects while letting others be managed? Thanks.

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• How to more effectively debug PHP code in the vein JavaScript with Firebug or XCode?

  - by racl101

  Hi everyone, I'm kind of a newbie with PHP so please bear with me. I would like to know if there was an effective way of debugging PHP code so that I don't have to have debugging messages display on the browser. For example, I find var_dump and print_r functions to be excellent for debugging variables, function calls and arrays respectively. The problem is I have been asked to debug code on a live site (no dev site, I know it is a horrible practice but this is not my project from the start.) So I would like to know what core function or php library or whatever else it is that I could use to log debugging calls in to log that I can check so I don't have to send debugging calls to the browser on a live site? I like the way you can use the console.log function in JavaScript code and check it in Firebug or the Webkit Console and I also like like the console window in Xcode and I was wondering if there was some similar tool for PHP debugging. Any extra info and pearls of wisdom would be greatly appreciated. Thanks, racl101.

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• Optimizing processing and management of large Java data arrays

  - by mikera

  I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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