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• Using VLC to Unicast High Definition Webcam over local gigabit LAN with low/zero delay

  - by Robin Day

  We're setting up a webcam "window" between two offices in the same buildilng. The two PC's are connected to the same gigabit switch. We're using VLC to stream the webcam over HTTP using the following commands. vlc dshow:// :dshow-caching="0" :dshow-size="640x480" :sout=#transcode{vcodec=h264,vb=0,scale=0}:http{mux=ffmpeg{mux=flv},dst=:8080/} :no-sout-rtp-sap :no-sout-standard-sap :ttl=1 :sout-keep vlc http://192.168.0.1:8080 :http-caching="0" Even with the caching set to zero, the delay in the image is a good 2-3 seconds. The CPU usage of each pc is also maxed. I'm guessing it's the transcoding that's causing much of the delay. Can anyone give me some changes to these command lines that will reduce the transcoding power, or send the webcam over a different protocol, or anything that will reduce the delay of the cameras? Bandwidth is not an issue at all as the pc's can be connected to a dedicated switch/vlan if required.

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• nginx static file buffer

  - by Philip

  I have a nfs which several frontend-servers are connected to for making the files stored on the nfs available for http downloads. It looks like I have problems with the way apache is serving the files, there seems to be a very small buffer or no buffer at all which results in a lot disk seeks. I did some testing with loading the whole requested file into memory at once and serve it to the client from memory. With this technique I need less disk seeks for a download stream. Since I don't want to implement this by myself for production use I thought that I could maybe use nginx for that because the documentation says that it uses buffers for static file serving. Is it possible to increase the buffer size to a few mb, if so which config parameter do I have to change for this? Has anyone experience with large buffers for static file serving? Is there a better way to reduce disk seeks?

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• Lighttpd referer issue

  - by Chris

  I have a problem to block files from accessing from different domains as my one. I have added to my lighty config in the "virual host" following: $HTTP["referer"] !~ "^($|http://www\.my-site\.net)" { url.access-deny = ( "" ) } but anyway the site www.example.com can access http://player.my-site.net/player.swf, also it can be accessed directly without a referrer. any idea? //EDIT here is my old apache .htaccess with a rewrite rule thats works perfect, but i dont know how to convert it for lighty: RewriteEngine on RewriteBase / RewriteCond %{HTTP_REFERER} !^http://my-site\.net/ [NC] RewriteCond %{HTTP_REFERER} !^http://www\.my-site\.net/ [NC] RewriteCond %{HTTP_REFERER} !^http://player\.my-site\.net/ [NC] RewriteCond %{HTTP_REFERER} !^http://stream\.my-site\.net/ [NC] RewriteRule .* - [L,R=404]

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• how to append a string to next line in perl

  - by tprayush

  hi all , i have a requirement like this.. this just a sample script... $ cat test.sh #!/bin/bash perl -e ' open(IN,"addrss"); open(out,">>addrss"); @newval; while (<IN>) { @col_val=split(/:/); if ($.==1) { for($i=0;$i<=$#col_val;$i++) { print("Enter value for $col_val[$i] : "); chop($newval[$i]=<STDIN>); } $str=join(":"); $_="$str" print OUT; } else { exit 0; } } close(IN); close(OUT); ' when i run this scipt... $ ./test.sh Enter value for NAME : abc Enter value for ADDRESS : asff35 Enter value for STATE : XYZ Enter value for CITY : EIDHFF Enter value for CONTACT : 234656758 $ cat addrss NAME:ADDRESS:STATE:CITY:CONTACT abc:asff35:XYZ:EIDHFF:234656758 when ran it second time $ cat addrss NAME:ADDRESS:STATE:CITY:CONTACT abc:asff35:XYZ:EIDHFF:234656758ioret:56fgdh:ghdgh:afdfg:987643221 ## it is appended in the same line... i want it to be added to the next line..... NOTE: i want to do this by explitly using the filehandles in perl....and not with redirection operators in shell. please help me!!!

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• GroupLayout: JScrollPane in TextArea is not working

  - by Dozent

  i'm new in java and recently started to develop an simple application. For the moment i have a problem with JScrollPanne, it's not able to scroll down (or up) when the text in textarea more than size of area. I have looked to some solutions, but all of them were for FlowLayot (GridLayout and BoxLayout), but not for GroupLayout. Here is the code: JPanel conent_p = new JPanel(); conent_p.setBorder(new TitledBorder(null, "", TitledBorder.LEADING, TitledBorder.TOP, null, null)); JLabel lblItemName = new JLabel("Item name:"); itemField = new JTextField(); itemField.setColumns(10); JLabel lblMxPrice = new JLabel("Max price:"); mpriceField = new JTextField(); mpriceField.setColumns(10); JLabel lblQuantity = new JLabel("Quantity:"); quanField = new JTextField(); quanField.setColumns(10); JLabel lblDelivery = new JLabel("Delivery:"); delivField = new JTextField(); delivField.setColumns(10); JLabel lblLogcat = new JLabel("LogCat:"); final JTextArea txtConsole = new JTextArea(); txtConsole.setEditable(false); txtConsole.setLineWrap(true); txtConsole.setWrapStyleWord(true); sbrText = new JScrollPane(txtConsole); sbrText.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); // Now create a new TextAreaOutputStream to write to our JTextArea control and wrap a // PrintStream around it to support the println/printf methods. PrintStream out = new PrintStream(new TextAreaOutputStream(txtConsole)); // redirect standard output stream to the TextAreaOutputStream System.setOut(out); // redirect standard error stream to the TextAreaOutputStream System.setErr(out); GroupLayout gl_conent_p = new GroupLayout(conent_p); gl_conent_p.setHorizontalGroup( gl_conent_p.createParallelGroup(Alignment.LEADING) .addGroup(gl_conent_p.createSequentialGroup() .addContainerGap() .addGroup(gl_conent_p.createParallelGroup(Alignment.LEADING) .addComponent(lblMxPrice, Alignment.TRAILING) .addComponent(lblItemName, Alignment.TRAILING) .addComponent(lblLogcat, Alignment.TRAILING)) .addGap(18) .addGroup(gl_conent_p.createParallelGroup(Alignment.LEADING) .addGroup(gl_conent_p.createSequentialGroup() .addGroup(gl_conent_p.createParallelGroup(Alignment.LEADING, false) .addComponent(itemField, GroupLayout.PREFERRED_SIZE, 365, GroupLayout.PREFERRED_SIZE) .addGroup(gl_conent_p.createSequentialGroup() .addComponent(mpriceField, GroupLayout.PREFERRED_SIZE, 80, GroupLayout.PREFERRED_SIZE) .addGap(18) .addComponent(lblQuantity) .addPreferredGap(ComponentPlacement.RELATED) .addComponent(quanField, 0, 0, Short.MAX_VALUE) .addGap(18) .addComponent(lblDelivery) .addPreferredGap(ComponentPlacement.RELATED) .addComponent(delivField, GroupLayout.PREFERRED_SIZE, 80, GroupLayout.PREFERRED_SIZE) .addPreferredGap(ComponentPlacement.RELATED))) .addGap(100)) .addGroup(gl_conent_p.createSequentialGroup() .addComponent(txtConsole, GroupLayout.PREFERRED_SIZE, 345, GroupLayout.PREFERRED_SIZE) .addComponent(sbrText) .addContainerGap()))) ); gl_conent_p.setVerticalGroup( gl_conent_p.createParallelGroup(Alignment.LEADING) .addGroup(gl_conent_p.createSequentialGroup() .addContainerGap() .addGroup(gl_conent_p.createParallelGroup(Alignment.BASELINE) .addComponent(lblItemName) .addComponent(itemField, GroupLayout.PREFERRED_SIZE, 20, GroupLayout.PREFERRED_SIZE)) .addGap(20) .addGroup(gl_conent_p.createParallelGroup(Alignment.LEADING) .addGroup(gl_conent_p.createParallelGroup(Alignment.BASELINE) .addComponent(lblDelivery) .addComponent(delivField, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)) .addGroup(gl_conent_p.createParallelGroup(Alignment.BASELINE) .addComponent(lblMxPrice) .addComponent(mpriceField, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE) .addComponent(lblQuantity) .addComponent(quanField, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE))) .addGap(55) .addGroup(gl_conent_p.createParallelGroup(Alignment.BASELINE) .addComponent(lblLogcat) .addComponent(txtConsole, GroupLayout.PREFERRED_SIZE, 200, GroupLayout.PREFERRED_SIZE) .addComponent(sbrText)) .addContainerGap()) ); conent_p.setLayout(gl_conent_p); getContentPane().add(conent_p, BorderLayout.NORTH); JButton btnBuy = new JButton("Buy"); btnBuy.addActionListener( new ActionListener() { public void actionPerformed(ActionEvent ev) { try { String title = itemField.getText().trim(); String mprice = mpriceField.getText().trim(); String quantity = quanField.getText().trim(); String deliver = delivField.getText().trim(); Item_CONCEPT item = new Item_CONCEPT(); item.setName(title); item.setDelivery(Integer.parseInt(deliver)); item.setStartPrice(0); item.setMaxPrice(Integer.parseInt(mprice)); myAgent.existsSeller(item); Date date = new Date(); DateFormat df = new SimpleDateFormat("dd.MM.yy HH:mm"); System.out.println(df.format(date)+": Buyer orders an item: "+item.getName()); //Clearing all fields itemField.setText(""); quanField.setText(""); delivField.setText(""); //txtConsole.setText(""); mpriceField.setText(""); } catch (Exception e) { JOptionPane.showMessageDialog(BuyerGUI.this, "A field is filled incorrectly. "+e.getMessage()+" is invalid.", "Error", JOptionPane.ERROR_MESSAGE); } } } );![enter image description here][1]

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• Building a network at home, what cables to use (if any)?

  - by Faruz

  My house is currently in ruins and am building it. While doing so, I wanted to design a home network. My main objectives are surfing and HD streaming. The house is one-level, 100 sq/m (about 300 sq/ft), and one of the rooms is a safety room with Reinforced concrete walls. About a year ago, when I started planning, I thought about putting Cat 6 STP cables in the walls and create network points in the rooms. Should I use STP or FTP? I heard that STP is a problem regarding connectors and stuff. Is it really beneficial? Will it work OK if I transfer the wire together with the telephone line? Should I maybe go with WLan and count on 802.11n to enable me to stream HD across the house? is 802.11n that good?

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• Content delivery: Alternatives to SHOUTcast

  - by polemon

  I've been using Icecast and SHOUTcast for several years now, to deliver audio and Video content. I wonder what kind of alternatives do I have to those two, especially when streaming video. On the client side, what software can I choose from to stream to those servers live? Making the streams available with Flash would be great, but that's maybe another story. We're still using EdCast, which is kinda dead by now, Shoutcast DSP plugin is not an option, as this tends to crash, etc. Are there any alternatives to that, when livestreaming video? I'm using Liquidsoap for content generation, mixing, etc. It should work with Icecast, Liquidsoap and if possible SHOUTcast.

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• how use graphvis in C# application?

  - by ghasedak -

  i have a dot format file and i download graphvis for windows now how can i use graphvis to show a graph in my c# application? using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using VDS.RDF; using VDS.RDF.Parsing; using VDS.RDF.Query; using System.IO; using System.Windows; using System.Runtime.InteropServices; using VDS.RDF.Writing; using System.Diagnostics; namespace WindowsFormsApplication2 { public partial class first : Form { Graph g = new Graph(); string s1 = null; /**************************************DATA********************************************/ public first() { InitializeComponent(); } private void button1_Click(object sender, EventArgs e) { Stream myStream = null; var parser = new Notation3Parser(); var graph = new Graph(); OpenFileDialog openFileDialog1 = new OpenFileDialog(); openFileDialog1.Filter = "RDF files (*.n3)|*.n3"; openFileDialog1.FilterIndex = 1; openFileDialog1.RestoreDirectory = true; openFileDialog1.Multiselect = false; if (openFileDialog1.ShowDialog() == DialogResult.OK) { try { if ((myStream = openFileDialog1.OpenFile()) != null) { using (myStream) { string s = openFileDialog1.FileName.ToString(); string w= Directory.GetCurrentDirectory().ToString(); string Fname = openFileDialog1.SafeFileName.ToString(); File.Copy(s,Path.Combine(w,Fname),true); // Insert code to read the stream here. Win32.AllocConsole(); s1 = Path.Combine(w, Fname); insertNodeButton.Visible = true; delBut.Visible = true; simi.Visible = true; showNodes showNodes1 = new showNodes(s1); g = showNodes1.returngraph(); Console.Read(); Win32.FreeConsole(); // g.SaveToFile("firstfile.n3"); this.Show(); } } } catch (Exception ex) { MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message); } } GraphVizWriter hi = new GraphVizWriter(); hi.Save(g, "c:\\ahmad.dot"); } private void button2_Click(object sender, EventArgs e) { string strCmdLine = Application.StartupPath + "\\Tools\\rdfEditor.exe"; //string strCmdLine = "DIR"; MessageBox.Show(strCmdLine); System.Diagnostics.Process process1; process1 = new System.Diagnostics.Process(); //Do not receive an event when the process exits. process1.EnableRaisingEvents = false; //The "/C" Tells Windows to Run The Command then Terminate System.Diagnostics.Process.Start(strCmdLine); process1.Close(); } private void Form1_Load(object sender, EventArgs e) { } private void insertNodeButton_Click(object sender, EventArgs e) { //Graph parentvalue = this.g; //String parentvalueadress = this.s1; addTriple a1 = new addTriple(); a1.G = g; a1.BringToFront(); a1.ShowDialog(); g = a1.G; g.SaveToFile("c:\\Hi.n3"); } this is my code i want to visul saly dot file format to show a graph with graphvis

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• LINQ .Cast() extension method fails but (type)object works.

  - by Ben Robinson

  To convert between some LINQ to SQL objects and DTOs we have created explicit cast operators on the DTOs. That way we can do the following: DTOType MyDTO = (LinqToSQLType)MyLinq2SQLObj; This works well. However when you try to cast using the LINQ .Cast() extension method it trows an invalid cast exception saying cannot cast type Linq2SQLType to type DTOType. i.e. the below does not work List<DTO.Name> Names = dbContact.tNames.Cast<DTO.Name>() .ToList(); But the below works fine: DAL.tName MyDalName = new DAL.tName(); DTO.Name MyDTOName = (DTO.Name)MyDalName; and the below also works fine List<DTO.Name> Names = dbContact.tNames.Select(name => (DTO.Name)name) .ToList(); Why does the .Cast() extension method throw an invalid cast exception? I have used the .Cast() extension method in this way many times in the past and when you are casting something like a base type to a derived type it works fine, but falls over when the object has an explicit cast operator.

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• Is this overly clever or unsafe?

  - by Liberalkid

  I was working on some code recently and decided to work on my operator overloading in c++, because I've never really implemented it before. So I overloaded the comparison operators for my matrix class using a compare function that returned 0 if LHS was less than RHS, 1 if LHS was greater than RHS and 2 if they were equal. Then I exploited the properties of logical not in c++ on integers, to get all of my compares in one line: inline bool Matrix::operator<(Matrix &RHS){ return ! (compare(*this,RHS)); } inline bool Matrix::operator>(Matrix &RHS){ return ! (compare((*this),RHS)-1); } inline bool Matrix::operator>=(Matrix &RHS){ return compare((*this),RHS); } inline bool Matrix::operator<=(Matrix &RHS){ return compare((*this),RHS)-1; } inline bool Matrix::operator!=(Matrix &RHS){ return compare((*this),RHS)-2; } inline bool Matrix::operator==(Matrix &RHS){ return !(compare((*this),RHS)-2); } Obviously I should be passing RHS as a const, I'm just probably not going to use this matrix class again and I didn't feel like writing another function that wasn't a reference to get the array index values solely for the comparator operation.

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• nginx bad gateway 502 with mono fastcgi

  - by Bradley Lederholz Leatherwood

  Hello so I have been trying to get my website to run on mono (on ubuntu server) and I have followed these tutorials almost to the letter: However when my directory is not blank fastcgi logs reveal this: Notice Beginning to receive records on connection. Error Failed to process connection. Reason: Exception has been thrown by the target of an invocation. I am not really sure what this means, and depending on what I do I can get another error that tells me the resource cannot be found: The resource cannot be found. Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable. Please review the following URL and make sure that it is spelled correctly. Requested URL: /Default.aspx/ Version information: Mono Runtime Version: 2.10.8 (tarball Thu Aug 16 23:46:03 UTC 2012) ASP.NET Version: 4.0.30319.1 If I should provide some more information please let me know. Edit: I am now getting a nginx gateway error. My nginx configuration file looks like this: server { listen 2194; server_name localhost; access_log $HOME/WWW/nginx.log; location / { root $HOME/WWW/dev/; index index.html index.html default.aspx Default.aspx Index.cshtml; fastcgi_index Views/Home/; fastcgi_pass 127.0.0.1:8000; include /etc/nginx/fastcgi_params; } } Running the entire thing with xsp4 I have discovered what the "Exception has been thrown by the target of an invocation." Handling exception type TargetInvocationException Message is Exception has been thrown by the target of an invocation. IsTerminating is set to True System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. Server stack trace: at System.Reflection.MonoCMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in :0 at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in :0 at System.Runtime.Serialization.ObjectRecord.LoadData (System.Runtime.Serialization.ObjectManager manager, ISurrogateSelector selector, StreamingContext context) [0x00000] in :0 at System.Runtime.Serialization.ObjectManager.DoFixups () [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.ObjectReader.ReadNextObject (System.IO.BinaryReader reader) [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.ObjectReader.ReadObjectGraph (BinaryElement elem, System.IO.BinaryReader reader, Boolean readHeaders, System.Object& result, System.Runtime.Remoting.Messaging.Header[]& headers) [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.NoCheckDeserialize (System.IO.Stream serializationStream, System.Runtime.Remoting.Messaging.HeaderHandler handler) [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize (System.IO.Stream serializationStream) [0x00000] in :0 at System.Runtime.Remoting.RemotingServices.DeserializeCallData (System.Byte[] array) [0x00000] in :0 at (wrapper xdomain-dispatch) System.AppDomain:DoCallBack (object,byte[]&,byte[]&) Exception rethrown at [0]: --- System.ArgumentException: Couldn't bind to method 'SetHostingEnvironment'. at System.Delegate.GetCandidateMethod (System.Type type, System.Type target, System.String method, BindingFlags bflags, Boolean ignoreCase, Boolean throwOnBindFailure) [0x00000] in :0 at System.Delegate.CreateDelegate (System.Type type, System.Type target, System.String method, Boolean ignoreCase, Boolean throwOnBindFailure) [0x00000] in :0 at System.Delegate.CreateDelegate (System.Type type, System.Type target, System.String method) [0x00000] in :0 at System.DelegateSerializationHolder+DelegateEntry.DeserializeDelegate (System.Runtime.Serialization.SerializationInfo info) [0x00000] in :0 at System.DelegateSerializationHolder..ctor (System.Runtime.Serialization.SerializationInfo info, StreamingContext ctx) [0x00000] in :0 at (wrapper managed-to-native) System.Reflection.MonoCMethod:InternalInvoke (System.Reflection.MonoCMethod,object,object[],System.Exception&) at System.Reflection.MonoCMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in :0 --- End of inner exception stack trace --- at (wrapper xdomain-invoke) System.AppDomain:DoCallBack (System.CrossAppDomainDelegate) at (wrapper remoting-invoke-with-check) System.AppDomain:DoCallBack (System.CrossAppDomainDelegate) at System.Web.Hosting.ApplicationHost.CreateApplicationHost (System.Type hostType, System.String virtualDir, System.String physicalDir) [0x00000] in :0 at Mono.WebServer.VPathToHost.CreateHost (Mono.WebServer.ApplicationServer server, Mono.WebServer.WebSource webSource) [0x00000] in :0 at Mono.WebServer.XSP.Server.RealMain (System.String[] args, Boolean root, IApplicationHost ext_apphost, Boolean quiet) [0x00000] in :0 at Mono.WebServer.XSP.Server.Main (System.String[] args) [0x00000] in :0

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• Haskel dot (.) and dollar ($) composition: correct use.

  - by Robert Massaioli

  I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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• postgresql 9.1 Multiple Cluster on same host

  - by user1272305

  I have 2 cluster databases, running on the same host, Ubuntu. My fist database port is set to default but my second database port is set to 5433 in the postgresql.conf file. While everything is ok with local connections, I cannot connect using any of my tools to the second database with port 5433, including pgAdmin. Please help. Any parameter that I need to modify for the new database with port 5433? netstat -an | grep 5433 shows, tcp 0 0 0.0.0.0:5433 0.0.0.0:* LISTEN tcp6 0 0 :::5433 :::* LISTEN unix 2 [ ACC ] STREAM LISTENING 72842 /var/run/postgresql/.s.PGSQL.5433 iptables -L shows, Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination

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• file copy error from system to cifs mount

  - by dwpriest

  When coping a file greater than 64kB from an Ubuntu server to a CIFS mounted windows share, most of the data is copied, but it seems the last chunk doesn't get copied. The size doesn't match, and the md5 check sums don't match. I have plenty of file space, but then I use cp, I get the following... cp: closing `cloudBackup/asdf.txt': No space left on device Using rsync, I get the following... rsync: close failed on "/home/fluffy/cloudBackup/.asdf.txt.qrBWe6": No space left on device (28) rsync error: error in file IO (code 11) at receiver.c(752) [receiver=3.0.8] rsync: connection unexpectedly closed (29 bytes received so far) [sender] rsync error: error in rsync protocol data stream (code 12) at io.c(601) [sender=3.0.8] I have full read/write permissions on the mounted share. I can copy via SSH just fine. Any ideas? Thank you

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• Fastest way to clamp a real (fixed/floating point) value?

  - by Niklas

  Hi, Is there a more efficient way to clamp real numbers than using if statements or ternary operators? I want to do this both for doubles and for a 32-bit fixpoint implementation (16.16). I'm not asking for code that can handle both cases; they will be handled in separate functions. Obviously, I can do something like: double clampedA; double a = calculate(); clampedA = a > MY_MAX ? MY_MAX : a; clampedA = a < MY_MIN ? MY_MIN : a; or double a = calculate(); double clampedA = a; if(clampedA > MY_MAX) clampedA = MY_MAX; else if(clampedA < MY_MIN) clampedA = MY_MIN; The fixpoint version would use functions/macros for comparisons. This is done in a performance-critical part of the code, so I'm looking for an as efficient way to do it as possible (which I suspect would involve bit-manipulation) EDIT: It has to be standard/portable C, platform-specific functionality is not of any interest here. Also, MY_MIN and MY_MAX are the same type as the value I want clamped (doubles in the examples above).

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• What is the rationale to not allow overloading of C++ conversions operator with non-member function

  - by Vicente Botet Escriba

  C++0x has added explicit conversion operators, but they must always be defined as members of the Source class. The same applies to the assignment operator, it must be defined on the Target class. When the Source and Target classes of the needed conversion are independent of each other, neither the Source can define a conversion operator, neither the Target can define a constructor from a Source. Usually we get it by defining a specific function such as Target ConvertToTarget(Source& v); If C++0x allowed to overload conversion operator by non member functions we could for example define the conversion implicitly or explicitly between unrelated types. template < typename To, typename From > operator To(const From& val); For example we could specialize the conversion from chrono::time_point to posix_time::ptime as follows template < class Clock, class Duration> operator boost::posix_time::ptime( const boost::chrono::time_point<Clock, Duration>& from) { using namespace boost; typedef chrono::time_point<Clock, Duration> time_point_t; typedef chrono::nanoseconds duration_t; typedef duration_t::rep rep_t; rep_t d = chrono::duration_cast<duration_t>( from.time_since_epoch()).count(); rep_t sec = d/1000000000; rep_t nsec = d%1000000000; return posix_time::from_time_t(0)+ posix_time::seconds(static_cast<long>(sec))+ posix_time::nanoseconds(nsec); } And use the conversion as any other conversion. For a more complete description of the problem, see here or on my Boost.Conversion library.. So the question is: What is the rationale to non allow overloading of C++ conversions operator with non-member functions?

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• Linq-to-XML explicit casting in a generic method

  - by vlad

  I've looked for a similar question, but the only one that was close didn't help me in the end. I have an XML file that looks like this: <Fields> <Field name="abc" value="2011-01-01" /> <Field name="xyz" value="" /> <Field name="tuv" value="123.456" /> </Fields> I'm trying to use Linq-to-XML to get the values from these fields. The values can be of type Decimal, DateTime, String and Int32. I was able to get the fields one by one using a relatively simple query. For example, I'm getting the 'value' from the field with the name 'abc' using the following: private DateTime GetValueFromAttribute(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == "abc" select (DateTime)field.Attribute("value")).FirstOrDefault() } this is placed in a separate function that simply returns this value, and everything works fine (since I know that there is only one element with the name attribute set to 'abc'). however, since I have to do this for decimals and integers and dates, I was wondering if I can make a generic function that works in all cases. this is where I got stuck. here's what I have so far: private T GetValueFromAttribute<T>(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == attName select (T)field.Attribute("value").Value).FirstOrDefault(); } this doesn't compile because it doesn't know how to convert from String to T. I tried boxing and unboxing (i.e. select (T) (Object) field.Attribute("value").Value but that throws a runtime Specified cast is not valid exception as it's trying to convert the String to a DateTime, for instance. Is this possible in a generic function? can I put a constraint on the generic function to make it work? or do I have to have separate functions to take advantage of Linq-to-XML's explicit cast operators?

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• How to configure Linux to act as a Bluetooth RFCOMM SPP server?

  - by regulatre

  I'm writing a phone app for Android that connects to a bluetooth RFCOMM device in my car. My phone app talks AT commands with it. For development work, I often need to communicate with the device to try different commands and things. My neighbors are starting to think I'm weird because I sit in my car for hours on end with my laptop screen shining on my face, typing away like a script kiddie. I'd much rather configure one of my many Linux servers to act as a bluetooth RFCOMM device and allow me to connect to it (indoors, while I sit on my couch). I imagine I have to start with something like sdptool add SP But then what? I'm perfectly happy writing a perl app to handle the I/O, but I just don't know how to make the bluez stack accept connections and subsequently pipe that stream to a perl app.

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• ATI driver in Fedora linux 11

  - by unknown (google)

  I recently built a pc with an ATI Radeon HD 5750. I have installed Fedora 11 and installed the device driver for the Radeon 5700 series proprietary drivers. I wanted to see if there is graphics hardware acceleration. I typed in glxinfo at the terminal and I got: X Error of failed request: BadRequest (invalid request code or no such operation) Major opcode of failed request: 135 (GLX) Minor opcode of failed request: 19 (X_GLXQueryServerString) Serial number of failed request: 14 Current serial number in output stream: 14 I don't know how to fix this. I tried to go to the ATI Catalyst Control Center; that worked, but the ATI Catalyst Control Center (Administrator) doesn't work. If anyone knows how to fix this problem then please let me know. Thanks

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• Haskell function composition (.) and function application ($) idioms: correct use.

  - by Robert Massaioli

  I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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• Reflection and Operator Overloads in C#

  - by TenshiNoK

  Here's the deal. I've got a program that will load a given assembly, parse through all Types and their Members and compile a TreeView (very similar to old MSDN site) and then build HTML pages for each node in the TreeView. It basically takes a given assembly and allows the user to create their own MSDN-like library for it for documentation purposes. Here's the problem I've run into: whenever an operator overload is encounted in a defined class, reflection returns that as a "MethodInfo" with the name set to something like "op_Assign" or "op_Equality". I want to be able to capture these and list them properly, but I can't find anything in the MethodInfo object that is returned to accurately identify that I'm looking at an operator. I definitely don't want to just capture everything that starts with "op_", since that will most certainly (at some point) will pick up a method it's not supposed to. I know that other methods and properties that are "special cases" like this one have the "IsSpecialName" property set, but appearantly that's not the case with operators. I've been scouring the 'net and wracking my brain to two days trying to figure this one out, so any help will be greatly appreciated.

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• C++: defining maximum/minimum limits for a class

  - by Luis

  Basically what the title says... I have created a class that models time slots in a variable-granularity daily schedule (where for example the first time slot is 30 minutes, but the second time slot can be 40 minutes); the first available slot starts at (a value comparable to) 1. What I want to do now is to define somehow the maximum and minimum allowable values that this class takes and I have two practical questions in order to do so: 1.- does it make sense to define absolute minimum and maximum in such a way for a custom class? Or better, does it suffice that a value always compares as lower-than any other possible value of the type, given the class's defined relational operators, to be defined the min? (and analogusly for the max) 2.- assuming the previous question has an answer modeled after "yes" (or "yes but ..."), how do I define such max/min? I know that there is std::numeric_limits<> but from what I read it is intended for "numeric types". Do I interpret that as meaning "represented as a number" or can I make a broader assumption like "represented with numbers" or "having a correspondence to integers"? After all, it would make sense to define the minimum and maximum for a date class, and maybe for a dictionary class, but numeric_limits may not be intended for those uses (I don't have much experience with it). Plus, numeric_limits has a lot of extra members and information that I don't know what to make with. If I don't use numeric_limits, what other well-known / widely-used mechanism does C++ offer to indicate the available range of values for a class?

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• Sound card problem, no audio device detected

  - by Paul

  I bought a new sound card because my built in sound card did not function. When I open YouTube, Media Player or anything that can create a sound my computer will hang up and sometimes when I start my computer it will hang when the Windows XP sound will activate. Update: My computer has no audio. It says NO AUDIO DEVICE. I already installed Realtek AC97 and Realtek High Definition Audio Driver and I also pasted stream.dll to the Windows and system32 folders and I restarted my computer but it still says NO AUDIO DEVICE. Please help me. Thanks

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• missing table in SQLite with specific version of HTC DESIRE HD

  - by William

  My application has a SQLite database in the asset folder. When the user launches my application, the database is created and the tables too. This works fine with a lot of devices (Nexus One, Htc Magic, SGS, X10… and even Htc Desire HD v2.2). My application works with all versions of Android (tested on my device (1.6, 2.2, 2.2.1 Htc Magic) and on the emulator (v1,5 until v2.3). I have just a problem with HTC DESIRE HD v2.2.1 1.72.405.3. The logcat: android.database.sqlite.SQLiteException: no such table: LISTE: , while compiling: select _id from LISTE at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2833) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2854) at android.app.ActivityThread.access$2300(ActivityThread.java:136) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2179) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:143) at android.app.ActivityThread.main(ActivityThread.java:5068) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:521) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) at dalvik.system.NativeStart.main(Native Method) Caused by: android.database.sqlite.SQLiteException: no such table: LISTE: , while compiling: select _id from LISTE at android.database.sqlite.SQLiteCompiledSql.native_compile(Native Method) at android.database.sqlite.SQLiteCompiledSql.compile(SQLiteCompiledSql.java:91) at android.database.sqlite.SQLiteCompiledSql.(SQLiteCompiledSql.java:64) at android.database.sqlite.SQLiteProgram.(SQLiteProgram.java:80) at android.database.sqlite.SQLiteQuery.(SQLiteQuery.java:46) at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:53) at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1417) at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1387) ... 11 more My application create the database but it doesn’t copy the tables of the file of the asset folder in data\data\packagename\databases\mydatabase. My code: public void createDataBase() throws IOException{ boolean dbExist = checkDataBase(); if(dbExist){ //do nothing - database already exist }else{ //By calling this method and empty database will be created into the default system path //of your application so we are gonna be able to overwrite that database with our database. this.getReadableDatabase(); try { copyDataBase(); } catch (IOException e) { throw new Error("Error copying database"); } } } private void copyDataBase() throws IOException{ //Open your local db as the input stream InputStream myInput = myContext.getAssets().open(DB_NAME); // Path to the just created empty db String outFileName = DB_PATH + DB_NAME; //Open the empty db as the output stream OutputStream myOutput = new FileOutputStream(outFileName); //transfer bytes from the inputfile to the outputfile byte[] buffer = new byte[1024]; int length; while ((length = myInput.read(buffer))!= -1){ if (length > 0){ myOutput.write(buffer, 0, length); } } //Close the streams myOutput.flush(); myOutput.close(); myInput.close(); } I think that the copydatabase function has a problem but I don't see. This code works fine with all devices except the HTC DESIRE HD v2.2.1 1.72.405.3. What problems might exist here for the HTC Desire with the given version above? How can this be remedied?

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• hosting simple python scripts in a container to handle concurrency, configuration, caching, etc.

  - by Justin Grant

  My first real-world Python project is to write a simple framework (or re-use/adapt an existing one) which can wrap small python scripts (which are used to gather custom data for a monitoring tool) with a "container" to handle boilerplate tasks like: fetching a script's configuration from a file (and keeping that info up to date if the file changes and handle decryption of sensitive config data) running multiple instances of the same script in different threads instead of spinning up a new process for each one expose an API for caching expensive data and storing persistent state from one script invocation to the next Today, script authors must handle the issues above, which usually means that most script authors don't handle them correctly, causing bugs and performance problems. In addition to avoiding bugs, we want a solution which lowers the bar to create and maintain scripts, especially given that many script authors may not be trained programmers. Below are examples of the API I've been thinking of, and which I'm looking to get your feedback about. A scripter would need to build a single method which takes (as input) the configuration that the script needs to do its job, and either returns a python object or calls a method to stream back data in chunks. Optionally, a scripter could supply methods to handle startup and/or shutdown tasks. HTTP-fetching script example (in pseudocode, omitting the actual data-fetching details to focus on the container's API): def run (config, context, cache) : results = http_library_call (config.url, config.http_method, config.username, config.password, ...) return { html : results.html, status_code : results.status, headers : results.response_headers } def init(config, context, cache) : config.max_threads = 20 # up to 20 URLs at one time (per process) config.max_processes = 3 # launch up to 3 concurrent processes config.keepalive = 1200 # keep process alive for 10 mins without another call config.process_recycle.requests = 1000 # restart the process every 1000 requests (to avoid leaks) config.kill_timeout = 600 # kill the process if any call lasts longer than 10 minutes Database-data fetching script example might look like this (in pseudocode): def run (config, context, cache) : expensive = context.cache["something_expensive"] for record in db_library_call (expensive, context.checkpoint, config.connection_string) : context.log (record, "logDate") # log all properties, optionally specify name of timestamp property last_date = record["logDate"] context.checkpoint = last_date # persistent checkpoint, used next time through def init(config, context, cache) : cache["something_expensive"] = get_expensive_thing() def shutdown(config, context, cache) : expensive = cache["something_expensive"] expensive.release_me() Is this API appropriately "pythonic", or are there things I should do to make this more natural to the Python scripter? (I'm more familiar with building C++/C#/Java APIs so I suspect I'm missing useful Python idioms.) Specific questions: is it natural to pass a "config" object into a method and ask the callee to set various configuration options? Or is there another preferred way to do this? when a callee needs to stream data back to its caller, is a method like context.log() (see above) appropriate, or should I be using yield instead? (yeild seems natural, but I worry it'd be over the head of most scripters) My approach requires scripts to define functions with predefined names (e.g. "run", "init", "shutdown"). Is this a good way to do it? If not, what other mechanism would be more natural? I'm passing the same config, context, cache parameters into every method. Would it be better to use a single "context" parameter instead? Would it be better to use global variables instead? Finally, are there existing libraries you'd recommend to make this kind of simple "script-running container" easier to write?

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