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  • Are licenses relevant for small code snippets?

    - by Martin
    When I'm about to write a short algorithm, I first check in the base class library I'm using whether the algorithm is implemented in it. If not, I often do a quick google search to see if someone has done it before (which is the case, 19 times out of 20). Most of the time, I find the exact code I need. Sometimes it's clear what license applies to the source code, sometimes not. It may be GPL, LGPL, BSD or whatever. Sometimes people have posted a code snippet on some random forum which solves my problem. It's clear to me that I can't reuse the code (copy/paste it into my code) without caring about the license if the code is in some way substantial. What is not clear to me is whether I can copy a code snippet containing 5 lines or so without doing a license violation. Can I copy/paste a 5-line code snippet without caring about the license? What about one-liner? What about 10 lines? Where do I draw the line (no pun intended)? My second problem is that if I have found a 10-line code snippet which does exactly what I need, but feel that I cannot copy it because it's GPL-licensed and my software isn't, I have already memorized how to implement it so when I go around implementing the same functionality, my code is almost identical to the GPL licensed code I saw a few minutes ago. (In other words, the code was copied to my brain and my brain after that copied it into my source code).

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  • Using sqldatareader in asp.net

    - by Phil
    I have this code to get data; s = "select documents.filename, documents.description, documents.filesize from documents, contentdocuments, content where contentdocuments.contentid = content.id and content.id = @contentid and contentdocuments.documentsid = documents.id ORDER BY documents.description" x = New SqlCommand(s, c) x.Parameters.Add("@contentid", SqlDbType.Int) x.Parameters("@contentid").Value = contentid c.Open() r = x.ExecuteReader If r.Read Then DownloadsRepeater.DataSource = r DownloadsRepeater.DataBind() **imagepath = "<img src='images/'" & getimage(r("filename")) & " border='0'** align='absmiddle'" End If c.Close() r.Close() The problem is on the line; imagepath = "<img src='images/'" & getimage(r("filename")) & " The error is; Invalid attempt to read when no data is present. How can I check to make sure data is present and get rid of this error? I thought the 'if r.read' did this? Thanks :EDIT: Function getimage(ByVal strin As String) As String If strin > "" Then dotpos = InStrRev(strin, ".") ext = Right(strin, Len(strin) - dotpos) getimage = ext & ".gif" End If Return getimage End Function

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  • How to validate presence of an uploaded file in rails?

    - by brad
    I'm playing around creating a rails file uploader and have struck a problem that should have an obvious solution. How do I check that a file has been selected in my form and uploaded? Here is my new.html.erb view <h2>Upload File</h2> <% form_for(@upload_file, :url => {:action => 'save'}, :html => {:multipart => true}) do |f| %> <%= f.error_messages %> <p> <%= f.label :file -%> <%= f.file_field :upload -%> </p> <p> <%= f.label :description %> <%= f.text_field :description %> </p> <p> <%= f.label :file_type %> <%= f.select :file_type, ["XML Data"] %> </p> <p><%= f.submit 'Upload File' %></p> <% end %> and here is my upload_file.rb model class UploadFile < ActiveRecord::Base validates_presence_of :description validates_presence_of :file_type validates_presence_of :upload def upload=(upload_file_field) self.name = "#{Time.now.strftime("%Y%m%d%H%M%S")}_#{upload_file_field.original_filename}" File.open("#{RAILS_ROOT}/public/upload/#{self.name}", "wb") { |f| f.write(upload_file_field.read) } end end If I use this as shown here, the validation validates_presence_of :upload always fails and I am returned to my form with an error message. I'd be very grateful if someone could explain how to do this validation correctly, and I'd be even more grateful if they could explain why it works. Thanks.

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  • MySQL GIS and Spatial Extensions - how to map regions and query against them

    - by chibineku
    I am trying to make a smartphone app which will return a list of users within a certain proximity, say 100m. It's easy to get the coordinates of my BlackBerry and write them to a database, but in order to return a list of other users within 100m, I need to pull every other record from the database and compare the distance between the two points, checking to see if it's within range, before outputting that user's information. This is going to be time consuming if there are many users involved. So I would like to map areas (countries, cities, I'm not yet sure of the resolution I'll need) so that I can first target a smaller subset of all users. This will save on processing time. I have read the basics of GIS and spatial querying on the mysql website but to be honest the query is over my head and I hate copying and pasting code without understanding it. Plus it only checks for proximity - I want to first check if a coordinate falls within a certain area. Does anyone have any experience of such matters and feel like giving me some pointers? Resources such as any preexisting databases of points describing countries as polygons would be really helpful too. Many thanks to anyone who takes the time :)

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  • ASP.net file operations delay

    - by mtranda
    Ok, so here's the problem: I'm reading the stream from a FileUpload control, reading in chunks of n bytes and writing the array in a loop until I reach the stream's end. Now the reason I do this is because I need to check several things while the upload is still going on (rather than doing a Save(); which does the whole thing in one go). Here's the problem: when doing this from the local machine, I can see the file just fine as it's uploading and its size increases (had to add a Sleep(); clause in the loop to actually get to see the file being written). However, when I upload the file from a remote machine, I don't get to see it until the the file has completed uploading. Also, I've added another call to write the progress to a text file as the progress is going on, and I get the same thing. Local: the file updates as the upload goes on, remote: the token file only appears after the upload's done (which is somewhat useless since I need it while the upload's still happening). Is there some sort of security setting in (or ASP.net) that maybe saves files in a temporary location for remote machines as opposed to the local machine and then moves them to the specified destination? I would liken this with ASP.net displaying error messages when browsing from the local machine (even on the public hostname) as opposed to the generic compilation error page/generic exception page that is shown when browsing from a remote machine (and customErrors are not off) Any clues on this? Thanks in advance.

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  • PInvokeStackImbalance -- C# with offreg.dll ( windows ddk7 )

    - by user301185
    I am trying to create an offline registry in memory using the offreg.dll provided in the windows ddk 7 package. You can find out more information on the offreg.dll here: MSDN Currently, while attempted to create the hive using ORCreateHive, I receive the following error: "Managed Debugging Assistant 'PInvokeStackImbalance' has detected a problem. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature." Here is the offreg.h file containing ORCreateHive: typedef PVOID ORHKEY; typedef ORHKEY *PORHKEY; VOID ORAPI ORGetVersion( __out PDWORD pdwMajorVersion, __out PDWORD pdwMinorVersion ); DWORD ORAPI OROpenHive ( __in PCWSTR lpHivePath, __out PORHKEY phkResult ); DWORD ORAPI ORCreateHive ( __out PORHKEY phkResult ); DWORD ORAPI ORCloseHive ( __in ORHKEY Handle ); The following is my C# code attempting to call the .dll and create the pointer for future use. using System.Runtime.InteropServices; namespace WindowsFormsApplication6 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } [DllImport("offreg.dll", CharSet = CharSet.Auto, EntryPoint = "ORCreateHive", SetLastError=true, CallingConvention = CallingConvention.StdCall)] public static extern IntPtr ORCreateHive2(); private void button1_Click(object sender, EventArgs e) { try { IntPtr myHandle = ORCreateHive2(); } catch (Exception r) { MessageBox.Show(r.ToString()); } } } } I have been able to create pointers in the past with no issue utilizing user32.dll, icmp.dll, etc. However, I am having no such luck with offreg.dll. Thank you.

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  • ASP.NET - I am generating an .XLS file with a DLL, how do I grant permissions for writing to file? (

    - by hamlin11
    I'm generating an .XLS file with a DLL (Excel Library http://code.google.com/p/excellibrary/) I've added this DLL as a reference to my project. The code to save the .XLS to disk is running, but it's encountering a permissions issue. I've attempted to set full access for IUSRS, Network Service, and Everyone just to see if I could get it working, and none of these seems to make a difference. Here's where I'm trying to write the file: c:/temp/test1.xls Here's the error: [SecurityException: Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.] System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet) +0 System.Security.CodeAccessPermission.Demand() +54 System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy) +2103 System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy) +138 System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share) +89 System.IO.File.Open(String path, FileMode mode, FileAccess access, FileShare share) +58 ExcelLibrary.Office.CompoundDocumentFormat.CompoundDocument.Create(String file) +88 ExcelLibrary.Office.Excel.Workbook.Save(String file) +73 CHC_Reports.LitAnalysis.CreateSpreadSheet_Click(Object sender, EventArgs e) in C:\Users\brian\Desktop\Enterprise Manager\CHC_Reports\LitAnalysis.aspx.vb:19 System.Web.UI.WebControls.Button.OnClick(EventArgs e) +115 System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +140 System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +29 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +11041511 System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +11041050 System.Web.UI.Page.ProcessRequest() +91 System.Web.UI.Page.ProcessRequest(HttpContext context) +240 ASP.litanalysis_aspx.ProcessRequest(HttpContext context) +52 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +599 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +171 Any idea what I need to do to diagnose the permissions issue and allow the file creation? Thanks.

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  • Why does only youtube embeds work on iPad?

    - by Nagaraj Hubli
    I am trying to find out as to why youtube embeds works just fine on iPad, and not the embeds of any other video site. Example of youtube embed: <object width="640" height="385"> <param name="movie" value="http://www.youtube.com/v/DlIU5TgwEFg&color1=0xb1b1b1&color2=0xcfcfcf&hl=en_US&feature=player_embedded&fs=1"></param> <param name="allowFullScreen" value="true"></param> <param name="allowScriptAccess" value="always"></param> <embed src="http://www.youtube.com/v/DlIU5TgwEFg&color1=0xb1b1b1&color2=0xcfcfcf&hl=en_US&feature=player_embedded&fs=1" type="application/x-shockwave-flash" allowfullscreen="true" allowScriptAccess="always" width="640" height="385"></embed> </object> is this because iPad has got a native youtube app which has special support for youtube embeds, or is this something that is handled by the script that's get executed by the youtube embed code, which might check for the user agent, and then load the HTML5 video player with a source pointing to the h.264 encoded version of the video (is something of this sort possible)?

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  • What is usefulness of W3C's Semantic Data Extractor in semantically correct XHTML CSS Development?

    - by metal-gear-solid
    What is the usefulness of W3C's Semantic Data Extractor? http://www.w3.org/2003/12/semantic-extractor.html This tool, geared by an XSLT stylesheet, tries to extract some information from a HTML semantic rich document. It only uses information available through a good usage of the semantics defined in HTML. The aim is to show that providing a semantically rich HTML gives much more value to your code: using a semantically rich HTML code allows a better use of CSS, makes your HTML intelligible to a wider range of user agents (especially search engines bots). As an aside, it can give clues to user agents developers on some hooks that could be interesting to add in their product. After checking validation for CSS and HTML. Should i go for Semantic Data Extractor tool. What it does. and how it can improved our coding.? Is anyone using it? And i check some site randomly with but with most of sites it gives error Using org.apache.xerces.parsers.SAXParser Exception net.sf.saxon.trans.XPathException: org.xml.sax.SAXParseException: The element type "input" must be terminated by the matching end-tag "`</input>`". org.xml.sax.SAXParseException: The element type "input" must be terminated by the matching end-tag "`</input>`".

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  • What is usefulness of W3C's "Semantic Data Extractor" in semantically correct XHTML CSS Development?

    - by metal-gear-solid
    What is the usefulness of W3C's Semantic Data Extractor? http://www.w3.org/2003/12/semantic-extractor.html This tool, geared by an XSLT stylesheet, tries to extract some information from a HTML semantic rich document. It only uses information available through a good usage of the semantics defined in HTML. The aim is to show that providing a semantically rich HTML gives much more value to your code: using a semantically rich HTML code allows a better use of CSS, makes your HTML intelligible to a wider range of user agents (especially search engines bots). As an aside, it can give clues to user agents developers on some hooks that could be interesting to add in their product. After checking validation for CSS and HTML. Should i go for Semantic Data Extractor tool. What it does. and how it can improved our coding.? Is anyone using it? And i check some site randomly with but with most of sites it gives error Using org.apache.xerces.parsers.SAXParser Exception net.sf.saxon.trans.XPathException: org.xml.sax.SAXParseException: The element type "input" must be terminated by the matching end-tag "`</input>`". org.xml.sax.SAXParseException: The element type "input" must be terminated by the matching end-tag "`</input>`". Is it possible to get pass every site with this tool? on one site i got this error No top-level heading (h1) found, no outline extracted. Is it necessary to have at least a H1 in any webpage?

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  • How to MakeTable ReadOnly including contents like images

    - by GustlyWind
    I have a table which has two text boxes and a image beside it to click and open a popup. In read-only mode based on condition I am able to make text boxes read-only but images are not becoming read-only.One solution I had is the anchor tag associated with image calls for JavaScript where I can check for a dummy click when it is in read-only mode. The problem here is the function is common and effects everywhere. So is there a way to make the entire table read-only so that no extra workaround needs to done. Edited for code <table> <tr> <td class="lightbg" colspan='4'>&nbsp; Expires:<input type="TEXT" value="" id="element1" name="expireDate" size="10" maxlength="20" class="" onChange="javascript:validateDateEntry('element1',true);;"> Period:<input type="TEXT" value="" id="element2" name="refershDate" size="10" maxlength="20" class="" onChange="javascript:validateDateEntry('element2',true);;"> &nbsp; <a href="javascript:doCalendar('element1');"> <img src="/PWM/images/images_2006/calendarbtn.gif" border="0" alt="Click to select date from calendar" align="absmiddle"> </a> </td> </tr> <tr> <td colspan='4'><b>*</b>Times are in the WFM Server's Time Zone.</td></tr> </table> Thanks

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  • Python Regular Expressions: Capture lookahead value (capturing text without consuming it)

    - by Lattyware
    I wish to use regular expressions to split words into groups of (vowels, not_vowels, more_vowels), using a marker to ensure every word begins and ends with a vowel. import re MARKER = "~" VOWELS = {"a", "e", "i", "o", "u", MARKER} word = "dog" if word[0] not in VOWELS: word = MARKER+word if word[-1] not in VOWELS: word += MARKER re.findall("([%]+)([^%]+)([%]+)".replace("%", "".join(VOWELS)), word) In this example we get: [('~', 'd', 'o')] The issue is that I wish the matches to overlap - the last set of vowels should become the first set of the next match. This appears possible with lookaheads, if we replace the regex as follows: re.findall("([%]+)([^%]+)(?=[%]+)".replace("%", "".join(VOWELS)), word) We get: [('~', 'd'), ('o', 'g')] Which means we are matching what I want. However, it now doesn't return the last set of vowels. The output I want is: [('~', 'd', 'o'), ('o', 'g', '~')] I feel this should be possible (if the regex can check for the second set of vowels, I see no reason it can't return them), but I can't find any way of doing it beyond the brute force method, looping through the results after I have them and appending the first character of the next match to the last match, and the last character of the string to the last match. Is there a better way in which I can do this? The two things that would work would be capturing the lookahead value, or not consuming the text on a match, while capturing the value - I can't find any way of doing either.

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  • Verizon SongID - How is it programmed?

    - by CheeseConQueso
    For anyone not familiar with Verizon's SongID program, it is a free application downloadable through Verizon's VCast network. It listens to a song for 10 seconds at any point during the song and then sends this data to some all-knowing algorithmic beast that chews it up and sends you back all the ID3 tags (artist, album, song, etc...) The first two parts and last part are straightforward, but what goes on during the processing after the recorded sound is sent? I figure it must take the sound file (what format?), parse it (how? with what?) for some key identifiers (what are these? regular attributes of wave functions? phase/shift/amplitude/etc), and check it against a database. Everything I find online about how this works is something generic like what I typed above. From audiotag.info This service is based on a sophisticated audio recognition algorithm combining advanced audio fingerprinting technology and a large songs' database. When you upload an audio file, it is being analyzed by an audio engine. During the analysis its audio “fingerprint” is extracted and identified by comparing it to the music database. At the completion of this recognition process, information about songs with their matching probabilities are displayed on screen.

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  • Can a standalone ruby script (windows and mac) reload and restart itself?

    - by user30997
    I have a master-workers architecture where the number of workers is growing on a weekly basis. I can no longer be expected to ssh or remote console into each machine to kill the worker, do a source control sync, and restart. I would like to be able to have the master place a message out on the network that tells each machine to sync and restart. That's where I hit a roadblock. If I were using any sane platform, I could just do: exec('ruby', __FILE__) ...and be done. However, I did the following test: p Process.pid sleep 1 exec('ruby', __FILE__) ...and on Windows, I get one ruby instance for each call to exec. None of them die until I hit ^C on the window in question. On every platform I tried this on, it is executing the new version of the file each time, which I have verified this by making simple edits to the test script while the test marched along. The reason I'm printing the pid is to double-check the behavior I'm seeing. On windows, I am getting a different pid with each execution - which I would expect, considering that I am seeing a new process in the task manager for each run. The mac is behaving correctly: the pid is the same for every system call and I have verified with dtrace that each run is trigging a call to the execve syscall. So, in short, is there a way to get a windows ruby script to restart its execution so it will be running any code - including itself - that has changed during its execution? Please note that this is not a rails application, though it does use activerecord.

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  • Javascript for conditional URL append or redirect based on window.location.href

    - by Wintermute
    ::Hi all:: I am trying to make a bookmarklet that when clicked will check the URL of the current tab\window to see if it contains 'char1' and\or 'char2' (a given character). If both chars are present it redirects to another URL, for the other two it will append the current URL respectively. I believe there must be a more elegant way of stating this than the following (which has so far worked perfectly for me) but I don't have great knowledge of Javascript. My (unwieldy & repetitive) working code (apologies): if (window.location.href.indexOf('char1')!=-1 && window.location.href.indexOf('char2')!=-1) {window.location="https://website.com/";} else if (window.location.href.indexOf('char1')!=-1) {window.location.assign(window.location.href+='append1');} else if (window.location.href.indexOf('char2')!=-1) {window.location.assign(window.location.href+='append2');} Does exactly what I need it to but, well... not very graceful to say the least. Is there a simpler way to do this, perhaps with vars or a pseudo-object? Or better code :D

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  • Mobile safari - suppress Unsupported Protocol alert

    - by Juriy
    Hello guys, I'm creating a website for iPhone and i use the native app (cliqcliq Quickpick) to upload photos. I use the script like the following to check if the application is installed. The basic idea is to send user to a custom url, if application is there it is launched, if it is not there the url should be ignored and user is taken to App Store. Below is the script: window.launchQuickpic = function() { var start = new Date(); setTimeout(function() { if (new Date() - start > 2000) { return; } window.location = 'http://www.cliqcliq.com/quickpic/install/'; }, 1000); var getParams = [...]; window.location = 'vquickpic://?' + getParams.join('&'); }; If the native app is not installed I'm getting the alert box saying that Safari does not recognize the custom url. After user clicks "ok" it works as it is supposed to. But the alert is reeealy annoying. I've tried to surround the window.location= code with try/catch. Didn't help.

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  • python eval weirdness

    - by amadain
    Hi Folks I have the following code in one of my classes along with checks when the code does not eval: filterParam="self.recipientMSISDN==tmpBPSS.split('_')[3].split('#')[0] and self.recipientIMSI==tmpBPSS.split('_')[3].split('#')[1]" if eval(filterParam): print "Evalled" else: print "Not Evalled\nfilterParam\n'%s'\ntmpBPSS\n'%s'\nself.recipientMSISDN\n'%s'\nself.recipientIMSI\n'%s'" % (filterParam, tmpBPSS, self.recipientMSISDN, self.recipientIMSI) I am not getting anything to 'eval'. Here are the results: Not Evalled filterParam 'self.recipientMSISDN==tmpBPSS.split('_')[3].split('#')[0] and self.recipientIMSI==tmpBPSS.split('_')[3].split('#')[1]' tmpBPSS 'bprm_DAILY_MO_919844000039#892000000' self.recipientMSISDN '919844000039' self.recipientIMSI '892000000' So I used the outputs from the above to check the code in a python shell and as you can see the code evalled correctly: >>> filterParam="recipientMSISDN==tmpBPSS.split('_')[3].split('#')[0] and recipientIMSI==tmpBPSS.split('_')[3].split('#')[1]" >>> tmpBPSS='bprm_DAILY_MO_919844000039#892000000' >>> recipientMSISDN='919844000039' >>> recipientIMSI='892000000' >>> if eval(filterParam): ... print "Evalled" ... else: ... print "Not Evalled" ... Evalled Am I off my rocker or what am I missing? A

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  • Simulating O_NOFOLLOW (2): Is this other approach safe?

    - by Daniel Trebbien
    As a follow-up question to this one, I thought of another approach which builds off of @caf's answer for the case where I want to append to file name and create it if it does not exist. Here is what I came up with: Create a temporary directory with mode 0700 in a system temporary directory on the same filesystem as file name. Create an empty, temporary, regular file (temp_name) in the temporary directory (only serves as placeholder). Open file name for reading only, just to create it if it does not exist. The OS may follow name if it is a symbolic link; I don't care at this point. Make a hard link to name at temp_name (overwriting the placeholder file). If the link call fails, then exit. (Maybe someone has come along and removed the file at name, who knows?) Use lstat on temp_name (now a hard link). If S_ISLNK(lst.st_mode), then exit. open temp_name for writing, append (O_WRONLY | O_APPEND). Write everything out. Close the file descriptor. unlink the hard link. Remove the temporary directory. (All of this, by the way, is for an open source project that I am working on. You can view the source of my implementation of this approach here.) Is this procedure safe against symbolic link attacks? For example, is it possible for a malicious process to ensure that the inode for name represents a regular file for the duration of the lstat check, then make the inode a symbolic link with the temp_name hard link now pointing to the new, symbolic link? I am assuming that a malicious process cannot affect temp_name.

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  • Best practice - When to evaluate conditionals of function execution

    - by Tesserex
    If I have a function called from a few places, and it requires some condition to be met for anything it does to execute, where should that condition be checked? In my case, it's for drawing - if the mouse button is held down, then execute the drawing logic (this is being done in the mouse movement handler for when you drag.) Option one says put it in the function so that it's guaranteed to be checked. Abstracted, if you will. public function Foo() { DoThing(); } private function DoThing() { if (!condition) return; // do stuff } The problem I have with this is that when reading the code of Foo, which may be far away from DoThing, it looks like a bug. The first thought is that the condition isn't being checked. Option two, then, is to check before calling. public function Foo() { if (condition) DoThing(); } This reads better, but now you have to worry about checking from everywhere you call it. Option three is to rename the function to be more descriptive. public function Foo() { DoThingOnlyIfCondition(); } private function DoThingOnlyIfCondition() { if (!condition) return; // do stuff } Is this the "correct" solution? Or is this going a bit too far? I feel like if everything were like this function names would start to duplicate their code. About this being subjective: of course it is, and there may not be a right answer, but I think it's still perfectly at home here. Getting advice from better programmers than I is the second best way to learn. Subjective questions are exactly the kind of thing Google can't answer.

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  • How can I make a Maybe-Transformer MaybeT into an instance of MonadWriter?

    - by martingw
    I am trying to build a MaybeT-Transformer Monad, based on the example in the Real World Haskell, Chapter Monad Transformers: data MaybeT m a = MaybeT { runMT :: m (Maybe a) } instance (Monad m) => Monad (MaybeT m) where m >>= f = MaybeT $ do a <- runMT m case a of Just x -> runMT (f x) Nothing -> return Nothing return a = MaybeT $ return (Just a) instance MonadTrans MaybeT where lift m = MaybeT $ do a <- m return (Just a) This works fine, but now I want to make MaybeT an instance of MonadWriter: instance (MonadWriter w m) => MonadWriter w (MaybeT m) where tell = lift . tell listen m = MaybeT $ do unwrapped <- listen (runMT m) return (Just unwrapped) The tell is ok, but I can't get the listen function right. The best I could come up with after 1 1/2 days of constructor origami is the one you see above: unwrapped is supposed to be a tuple of (Maybe a, w), and that I want to wrap up in a Maybe-Type and put the whole thing in an empty MonadWriter. But the compiler complains with: Occurs check: cannot construct the infinite type: a = Maybe a When generalising the type(s) for `listen' In the instance declaration for `MonadWriter w (MaybeT m)' What am I missing?

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  • Compressibility Example

    - by user285726
    From my algorithms textbook: The annual county horse race is bringing in three thoroughbreds who have never competed against one another. Excited, you study their past 200 races and summarize these as prob- ability distributions over four outcomes: first (“first place”), second, third, and other. Outcome Aurora Whirlwind Phantasm 0.15 0.30 0.20 first 0.10 0.05 0.30 second 0.70 0.25 0.30 third 0.05 0.40 0.20 other Which horse is the most predictable? One quantitative approach to this question is to look at compressibility. Write down the history of each horse as a string of 200 values (first, second, third, other). The total number of bits needed to encode these track- record strings can then be computed using Huffman’s algorithm. This works out to 290 bits for Aurora, 380 for Whirlwind, and 420 for Phantasm (check it!). Aurora has the shortest encoding and is therefore in a strong sense the most predictable. How did they get 420 for Phantasm? I keep getting 400 bytes, as so: Combine first, other = 0.4, combine second, third = 0.6. End up with 2 bits encoding each position. Is there something I've misunderstood about the Huffman encoding algorithm? Textbook available here: http://www.cs.berkeley.edu/~vazirani/algorithms.html (page 156).

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  • Do you use an architectural framework for Flex/AIR development?

    - by Christophe Herreman
    Given that Flex is still a relatively young technology, there are already a bunch of architectural frameworks available for Flex/AIR (and Flash) development, the main ones being Cairngorm and PureMVC. The amount of architectural frameworks is remarkable compared to other technologies. I was wondering how many of you use an architectural framework for Flex development. If so, why, or why not if you don't use any? To share my own experience and point of view: I have used Cairngorm (and ARP for Flash development) on a variety of projects and found that at times, we needed to write extra code just to fit into the framework, which obviously didn't feel right. Although I haven't used PureMVC on many occasions, I have the same gut feeling after looking at the examples applications. Architectural frameworks equal religion in some way. Most followers are convinced that their framework is THE framework and are not open or very skeptical when it comes to using other frameworks. (I also find myself hesitant and skeptical to check out new frameworks, but that is mainly because I would rather wait until the hype is over.) In conclusion, I'm thinking that it is better to have a sound knowledge of patterns and practices that you can apply in your application instead of choosing a framework and sticking to it. There is simply no right or wrong and I don't believe that there will ever be a framework that is considered the holy grail.

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  • Enumerating a string

    - by JamesB
    I have a status which is stored as a string of a set length, either in a file or a database. I'm looking to enumerate the possible status' I have the following type to define the possible status' Type TStatus = (fsNormal = Ord('N'),fsEditedOnScreen = Ord('O'), fsMissing = Ord('M'),fsEstimated = Ord('E'),fsSuspect = Ord('s'), fsSuspectFromOnScreen = Ord('o'),fsSuspectMissing = Ord('m'), fsSuspectEstimated = Ord('e')); Firstly is this really a good idea? or should I have a seperate const array storing the char conversions? That would mean more than one place to update. Now convert a string to a status array I have the following, but how can I check if a char is valid without looping through the enumeration? Function StrToStatus(Value : String):TStatusArray; var i: Integer; begin if Trim(Value) = '' then begin SetLength(Result,0); Exit; end; SetLength(Result,Length(Value)); for i := 1 to Length(Value) do begin Result[i] := TStatus(Value[i]); // I don't think this line is safe. end; end; AFAIK this should be fine for converting back again. Function StatusToStr(Value : TStatusArray):String; var i: Integer; begin for i := 0 to Length(Value) - 1 do Result := Result + Chr(Ord(Value[i])) end; I'm using Delphi 2007

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  • How do I load an XML document, add and remove nodes, then apply it to a ASP DataGrid control?

    - by JFOX
    I have a pretty simple operation but am struggling with how to implement it. I am loading XML from an external data source using a DataSet.ReadXml(), the creating a new XMLDataDocument from that data set, then syncing the Dataset back to the XMLDataDocument like so: doc = new XmlDataDocument(dsDataSet); dsDataSet.EnforceConstraints = false; dsDataSet= doc.DataSet; Once loaded I do two things to the XmlDataDocument: Loop through and check if a purely meta node, count, exists right beneath the root node and if so remove it. a thumb node exists in a second level nodelist and if not, create and append it. This is all going a expected because the result of doc.save() looks correct. Where I'm having an issue is updating the Dataset, which is being applied as the data source for an ASP DataGrid. Once all the above XMLDoc manipaulation is done I do this: dsDataSet.Merge(doc.DataSet); dsDataSet.AcceptChanges(); I then apply the data set to the grid control: dgList.DataSource = dsDataSet; dgList.DataBind(); But, when I do this I get this error on the site: System.Web.HttpException: DataBinding: 'System.Data.DataRowView' does not contain a property with the name 'thumb'. What did I miss?

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  • Using a UITableViewController with a small-sized table?

    - by rpj
    When using a UITableViewController, the initWithStyle: method automatically creates the underlying UITableView with - according to the documentation - "the correct dimensions". My problem is that these "correct dimensions" seem 320x460 (the iPhone's screen size), but I'm pushing this TableView/Controller pair into a UINavigationController which is itself contained in a UIView, which itself is about half the height of the screen. No frame or bounds wrangling I can come up with seems to correctly reset the table's size, and as such it's "too long", meaning there are a collection of rows that are pushed off the bottom of the screen and are not visible nor reachable by scrolling. So my question comes down to: what is the proper way to tell a UITableViewController to resize its component UITableView to a specified rectangle? Thanks! Update I've tried all the techniques suggested here to no avail, but I did find one interesting thing: if I eschew the UINavigationController altogether (which I'm not yet willing to do for production, but as an experiment), and add the table view as a direct subview of the enclosing view I mentioned, the frame size given is respected. The very moment I re-introduce the UINavigationController into the mix, no matter if it is added as a subview before or after the table view, and no matter if alloc/init it before or after the table view is added as a subview, the result is the same as it was before. I'm beginning to suspect UINavigationController isn't much of a team player... Update 2 The suggestion to check frame size after the table view on screen was a good one: turns out that the navigation controller is in fact resizing it some time in between load and display. My solution, hacky at best, has been to cache the frame given on load and to reset it if changed at the beginning of tableView:cellForRowAtIndexPath:. Why there you ask? Because it's the one place I found that worked, that's why! I don't consider this a solution as it's obviously improper, but for the benefit of anyone else reading, it does seem to work.

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