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• When copying VM filesystem over netcat, dd copies double the disk size

  - by JivanAmara

  I'm attempting to copy the disk of a working headless virtualbox VM (VM1) on one server to a new VM (VM2) on a vCloud server. I don't have access to the host of VM2. The OS is Windows Server 2003 (32-bit) I start both VMs with a live Knoppix image. I run 'nc -l | dd of=/dev/sda bs=512' on VM2 I run 'dd if=/dev/sda bs=512 | nc ' on VM1 I previously did this with another windows VM and it worked fine. VM1 has a disk of size ~70GB (verified with fdisk); however, the amount of data dd reports read/written is ~139GB. Of course the target machine doesn't work properly. I get a Windows splash screen, then blue error screen with general 'system not working' information. I'm at a loss what could cause this. Any ideas?

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• Double try_files to solve the nginx's "No input file specified" issue

  - by Howard

  I am following the nginx's wiki (http://wiki.nginx.org/WordPress) to setup my wordpress location / { try_files $uri $uri/ /index.php?$args; } By using the above lines, when a static file which is not found it will redirect to index.php of wordpress, that is okay but.. Problem: When I request an non-existence php script, e.g. http://www.example.com/foo.php, nginx will give me No input file specified I want nginx to return 404 instead of the above message, so in the main fcgi config, I add the 2nd try_files location ~ \.php$ { try_files $uri =404; fastcgi_split_path_info ^(.+\.php)(/.+)$; include /etc/nginx/fastcgi_params; ... } And this worked, but I am looking if there are any better way to handle it?

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• Benefits of a RAID BBU in addition to a double UPS + PS system

  - by Wikser

  Today I roughly measured the benefits of enabling write-back on the RAID controller on a server at work. It got no RAID battery-backup-unit (BBU) so the write-cache is currently disabled. As the server is not used to capacity (by far), the results in most test were spectacular, e.g.: Database CRUD: before 35s, after 4s Saving a 1MB Excel file: before: 20s (!), after: 0.5s Of course having a BBU is always recommended, but what are the main benefits of installing a BBU to a system, which got redundant power supplies and is attached to UPSs? Does this depend on the type of the system (database, file, terminal)? What is a realistic fail scenario which could be prevented by a BBU? Thanks in advance!

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• SSH not working through Double NAT

  - by d_inevitable

  I am trying to setup port forwarding for ssh through 2 NATs The first Router translates my internet IP to my outer network (10.1.7.0). In the outer network there's a second Router that does NAT to my inner network (192.168.1.0). The target server is connected to both, the outer network and the inner network. I cannot change the port forwarding options for outer router. It is currently configured to forward the SSH and HTTP port to the router for the inner network. Internet + | v +-----------------+ +------------------+ | Outer Router | | Inner Router | |-----------------| |------------------| | | SSH HTTP | | +----+ +--------------------->| | | | | | | | | | | | | +-------+---------+ +------+---------+-+ | | | | | | | | | | | | | | +------------------+ | SSH | | | | Server | | | | | |------------------| | | | +-----------> |<-------+ | | | | |HTTP (testing) | +------------------+ | | | +------v------------------+ | | Outer Workstation | +-------------------+ | |-------------------------| | Inner Workstation| | | | |-------------------| | | | | |<----------------+ +-------------------------+ | | +-------------------+ When connecting from a outer workstation to the address of the inner router, then both SSH and HTTP work fine. When connecting from the internet to my public ip with HTTP, the connection works fine as well. However SSH just times out. Most likely because the reply is not routed back properly. I suspect its either because of the SSH itself, or because the server is connected to both, the inner and outer network. Any ideas how I could resolve this issue? The routes on the server are currently: ip route show default via 10.1.7.254 dev eth0 metric 100 10.1.7.0/24 dev eth0 proto kernel scope link src 10.1.7.1 192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.2 Do I have to change this? If so how?

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• Finding bluetooth link key in Win7, to double pair a device on dualboot computer

  - by Ilari Kajaste

  How can I dig up the bluetooth link key for a paired device in Win7? Is this something that is dependent on the bluetooth stack I'm using (Toshiba), or is there a generic place to store these in Win7? Note: I'm not talking about the six-digit code usually typed by the user during pairing - that is worthless since it's discarded after pairing process. What I mean is the 128-bit link key that the devices exchange during pairing, and use thereafter to encrypt all their bluetooth traffic. Background: I dualboot Win7 / Ubuntu on my laptop, and I would like to have my phone paired to both OS's. Since the dualbooting computer has only one bluetooth adapter and thus only one bluetooth address, I cannot do two pairings to the phone, since on the second pairing (windows) the phone just replaces the previous pairing (linux) to the same bluetooth address. A thread on Ubuntu forums pointed me to what I have to do - pair first on linux, then on windows, and then replace the link key on linux side with the one windows negotiated. I can find the linux side pairing key from /var/lib/bluetooth/[BD_ADDR]/linkkeys - no problems there. However, on windows side I can't find the key. According to the forum post, on windows side the key should be in SYSTEM\ControlSet002\services\BTHPORT\Parameters\Keys\[BD_ADDR] but while that registry key does exist, it has no subkeys. (And a similar registry path in ControlSet001 didn't have any subkeys either.) One thing I've been instructed to do is to capture all events during pairing with Sysinternals Process Monitor. I did this, but I haven't been able to find any useful information from the captured events, not even by exporting the data to a huge XML and grepping that with the BD_ADDRs (with or without colons). So how could I find the link key for a paired device in Win7? Some reference information: Wikipedia: Bluetooth, Security Now: Bluetooth security

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• SFTP over double server hop

  - by josh.trow

  I'm trying to work out a method to allow me to access files on an SFTP server than I cannot access from my local machine. Currently, I have to SSH to a remote server (it is in a certain IP block that the final SFTP server will accept from), then from there SFTP to the destination server. From there, I get the files I am interested in, thereby dropping them onto the middleman server, from which I can get the files either over a Samba share or with a direct scp. I also work in the reverse, where I drop the files onto the middleman, SSH to it then SFTP to the destination and put them into the appropriate folders. My goal is to shorten this. The unfortunate restrictions are that my machine is Windows (I use KiTTy and/or Cygwin) and I cannot modify the middleman server (or destination server) in any way. I am willing to use command line or GUI programs so long as it works and is free. Any ideas?

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• Double external monitors on a iMac

  - by Josh K

  Possible to use two externals? I know there is only one port in the back, but is there an adapter / way it can be done?

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• RSAT and double accounts

  - by Ryaner

  Since we are looking at migrating our domain admins to use non domain-admin accounts and runas for admin tasks a discussion has begun. How do others use RSAT with runas? I know you can Shift+RightClick run as other user to launch it with admin rights, but it looses the icon on the taskbar. The question also has been put, why do Microsoft release the RSAT tools if they recommend admins to run using non-domain accounts. Edit: Further to this, some of the initial testing with RSAT via the run as other user command hasn't worked out well. Few of the options don't function in the Hyper-V and Failover Cluster Manager.

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• Access remote server with Nautilus through double SSH tunnel

  - by D W

  I'm trying to access my work computer from home. We are supposed to SSH into a server, say ssh.company.com and from there ssh into an xhost to to work, say xhost04.company.com. xhost04 is not directly accessible. How can I browse files on xhost04 from my home computer using nautilus (in ubuntu). To access the SSH host I would use: sftp://ssh.company.com/

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• Adding click/double-click events to static group box controls

  - by omatai

  Having realised my own reasons were way too dubious, I've now gone about this a different way. But I'm still curious... For reasons of nostalgia, familiarity and laziness, I'm coding a UI with MFC. For dubious reasons (as if those were not enough), I wanted to add a (double-)click event to a group box. Naturally, the group box contains things - in fact, it contains another static item, to which I can successfully add a (double-)click event handler. Is there any reason I cannot get an event handler to work for clicks on my group box the same way I can do that for the simple text static item? No amount of clicking on, in or near the control fires the event. Note - I've read through http://www.codeproject.com/KB/static/staticctrl_tut.aspx and tried responding to both ON_STN_... events and ON_BN_... messages, setting the notify style (BS_NOTIFY appears in the rc file)... and still I'm missing something - what is it? Is it even possible? Most of what I've googled suggests it is... but without clear answers for C++/MFC. Since first posting this question, I've found reference to a WM_NCHITTEST message, and hints that you have to create a handler for this message to override the group box default behaviour of responding with HT_TRANSPARENT... despite having its transparent property in ClassWizard set to false. Hmmm. Can anyone confirm that this is indeed the key?

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• JOGL Double Buffering

  - by Bar

  What is eligible way to implement double buffering in JOGL (Java OpenGL)? I am trying to do that by the following code: ... /** Creating canvas. */ GLCapabilities capabilities = new GLCapabilities(); capabilities.setDoubleBuffered(true); GLCanvas canvas = new GLCanvas(capabilities); ... /** Function display(…), which draws a white Rectangle on a black background. */ public void display(GLAutoDrawable drawable) { drawable.swapBuffers(); gl = drawable.getGL(); gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT); gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f); gl.glColor3f(1.0f, 1.0f, 1.0f); gl.glBegin(GL.GL_POLYGON); gl.glVertex2f(-0.5f, -0.5f); gl.glVertex2f(-0.5f, 0.5f); gl.glVertex2f(0.5f, 0.5f); gl.glVertex2f(0.5f, -0.5f); gl.glEnd(); } ... /** Other functions are empty. */ Questions: — When I'm resizing the window, I usually get flickering. As I see it, I have a mistake in my double buffering implementation. — I have doubt, where I must place function swapBuffers — before or after (as many sources says) the drawing? As you noticed, I use function swapBuffers (drawable.swapBuffers()) before drawing a rectangle. Otherwise, I'm getting a noise after resize. So what is an appropriate way to do that? Including or omitting the line capabilities.setDoubleBuffered(true) does not make any effect.

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• Theme confusion in SpreadsheetML.

  - by dmaruca

  I've been fighting this all day. Inside my styles.xml file I have color information given like so: <fgColor theme="0" tint="-0.249977111117893" / ECMA 376 defines a theme color reference as: Index into the <clrScheme collection, referencing a particular <sysClr or <srgbClr value expressed in the Theme part. Ok, that sounds easy. Here is an excerpt from my clrScheme xml: <a:clrScheme name="Office" <a:dk1 <a:sysClr val="windowText" lastClr="000000" / </a:dk1 <a:lt1 <a:sysClr val="window" lastClr="FFFFFF" / </a:lt1 Index zero is black, and they are wanting to darken it? I can tell you that after the tint is applied, the color should be #F2F2F2. My confusion is what does theme="0" really mean? It can't possible mean to darken #000000. Checking MSDN only confuses me even more. From http://msdn.microsoft.com/en-us/library/dd560821.aspx note that the theme color integer begins counting from left to right in the palette starting with zero. Theme color 3 is the dark 2 text/background color. Actually, if you start counting at zero the third entry is Light 2. Dark 2 is the second one. Can anyone here shed some light on this subject for me? What does theme="0" really mean? Here is the VB6 code I have been working with to apply the tint. You can paste it into your vba editor and run the test sub. Public Type tRGB R As Byte G As Byte B As Byte End Type Public Type tHSL H As Double S As Double L As Double End Type Sub TestRgbTint() Dim c As tRGB RGB_Hex2Type "ffffff", c RGB_ApplyTint c, -0.249977111117893 Debug.Print Hex(c.R) & Hex(c.G) & Hex(c.B) End Sub Public Sub RGB_Hex2Type(ByVal HexString As String, RGB As tRGB) 'Remove the alpha channel if it exists If Len(HexString) = 8 Then HexString = mID(HexString, 3) End If RGB.R = CByte("&H" & Left(HexString, 2)) RGB.G = CByte("&H" & mID(HexString, 3, 2)) RGB.B = CByte("&H" & Right(HexString, 2)) End Sub Public Sub RGB_ApplyTint(RGB As tRGB, tint As Double) Const HLSMAX = 1# Dim HSL As tHSL If tint = 0 Then Exit Sub RGB2HSL RGB, HSL If tint < 0 Then HSL.L = HSL.L * (1# + tint) Else HSL.L = HSL.L * (1# - tint) + (HLSMAX - HLSMAX * (1# - tint)) End If HSL2RGB HSL, RGB End Sub Public Sub HSL2RGB(HSL As tHSL, RGB As tRGB) HSL2RGB_ByVal HSL.H, HSL.S, HSL.L, RGB End Sub Private Sub HSL2RGB_ByVal(ByVal H As Double, ByVal S As Double, ByVal L As Double, RGB As tRGB) Dim v As Double Dim R As Double, G As Double, B As Double 'Default color to gray R = L G = L B = L If L < 0.5 Then v = L * (1# + S) Else v = L + S - L * S End If If v > 0 Then Dim m As Double, sv As Double Dim sextant As Integer Dim fract As Double, vsf As Double, mid1 As Double, mid2 As Double m = L + L - v sv = (v - m) / v H = H * 6# sextant = Int(H) fract = H - sextant vsf = v * sv * fract mid1 = m + vsf mid2 = v - vsf Select Case sextant Case 0 R = v G = mid1 B = m Case 1 R = mid2 G = v B = m Case 2 R = m G = v B = mid1 Case 3 R = m G = mid2 B = v Case 4 R = mid1 G = m B = v Case 5 R = v G = m B = mid2 End Select End If RGB.R = R * 255# RGB.G = G * 255# RGB.B = B * 255# End Sub Public Sub RGB2HSL(RGB As tRGB, HSL As tHSL) Dim R As Double, G As Double, B As Double Dim v As Double, m As Double, vm As Double Dim r2 As Double, g2 As Double, b2 As Double R = RGB.R / 255# G = RGB.G / 255# B = RGB.B / 255# 'Default to black HSL.H = 0 HSL.S = 0 HSL.L = 0 v = IIf(R > G, R, G) v = IIf(v > B, v, B) m = IIf(R < G, R, G) m = IIf(m < B, m, B) HSL.L = (m + v) / 2# If HSL.L < 0 Then Exit Sub End If vm = v - m HSL.S = vm If HSL.S > 0 Then If HSL.L <= 0.5 Then HSL.S = HSL.S / (v + m) Else HSL.S = HSL.S / (2# - v - m) End If Else Exit Sub End If r2 = (v - R) / vm g2 = (v - G) / vm b2 = (v - B) / vm If R = v Then If G = m Then HSL.H = 5# + b2 Else HSL.H = 1# - g2 End If ElseIf G = v Then If B = m Then HSL.H = 1# + r2 Else HSL.H = 3# - b2 End If Else If R = m Then HSL.H = 3# + g2 Else HSL.H = 5# - r2 End If End If HSL.H = HSL.H / 6# End Sub

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• C# - InvalidCastException when fetching double from sqlite

  - by Irro

  I keep getting a InvalidCastException when I'm fetching any double from my SQLite database in C#. The exception says "Specified cast is not valid." I am able to see the value in a SQL manager so I know it exists. It is possible to fetch Strings (VARCHARS) and ints from the database. I'm also able to fetch the value as an object but then I get "66.0" when it's suppose to be "66,8558604947586" (latitude coordination). Any one who knows how to solve this? My code: using System.Data.SQLite; ... SQLiteConnection conn = new SQLiteConnection(@"Data Source=C:\\database.sqlite; Version=3;"); conn.Open(); SQLiteDataReader reader = getReader(conn, "SELECT * FROM table"); //These are working String name = reader.GetString(1); Int32 value = reader.GetInt32(2); //This is not working Double latitude = reader.getDouble(3); //This gives me wrong value Object o = reader[3]; //or reader["latitude"] or reader.getValue(3)

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• detecting double free object, release or not release ...

  - by mongeta

  Hello, If we have this code in our interface .h file: NSString *fieldNameToStoreModel; NSFetchedResultsController *fetchedResultsController; NSManagedObjectContext *managedObjectContext; DataEntered *dataEntered; In our implementation file .m we must have: - (void)dealloc { [fieldNameToStoreModel release]; [fetchedResultsController release]; [managedObjectContext release]; [dataEntered release]; [super dealloc]; } The 4 objects are assigned from a previous UIViewController, like this: UIViewController *detailViewController; detailViewController = [[CarModelSelectViewController alloc] initWithStyle:UITableViewStylePlain]; ((CarModelSelectViewController *)detailViewController).dataEntered = self.dataEntered; ((CarModelSelectViewController *)detailViewController).managedObjectContext = self.managedObjectContext; ((CarModelSelectViewController *)detailViewController).fieldNameToStoreModel = self.fieldNameToStoreModel; [self.navigationController pushViewController:detailViewController animated:YES]; [detailViewController release]; The objects that now live in the new UIViewController, are the same as the previous UIViewController, and I can't release them in the new UIViewController ? The problems is that sometimes, my app crashes when I leave the new UIViewController and go to the previous one, not always. Normally the error that I'm getting is a double free object. I've used the malloc_error_break but I'm still not sure wich object is. Sometimes I can go from the previous UIViewController to the next one and come back 4 or 5 times, and the double free object appears. If I don't release any object, all is working and Instruments says that there are no memory leaks ... So, the final question, should I release those objects here or not ? Thanks, m.

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• Double buffering C#

  - by LmSNe

  Hey, I'm trying to implement the following method: void Ball::DrawOn(Graphics g); The method should draw all previous locations(stored in a queue) of the ball and finally the current location. I don't know if that matters, but I print the previous locations using g.DrawEllipse(...) and the current location using g.FillEllipse(...). The question is, that as you could imagine there is a lot of drawing to be done and thus the display starts to flicker much. I had searched for a way to double buffer, but all I could find is these 2 ways: 1) System.Windows.Forms.Control.DoubleBuffered = true; 2) SetStyle(ControlStyles.DoubleBuffer | ControlStyles.UserPaint | ControlStyles.AllPaintingInWmPaint, true); while trying to use the first, I get the an error explaining that from in this method the Property DoubleBuffered is inaccessible due to its protection level. While I can't figure how to use the SetStyle method. Is it possible at all to double buffer while all the access I have is to the Graphics Object I get as input in the method? Thanks in Advance,

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• Php/Regex get the contents between a set of double quotes

  - by Davy Arnold

  Update to my question: My goal overall is to split the string into 4 parts that I can access later. value = " result of the html inside the first and last " " Here is an example of what i'm trying to do: // My string (this is dynamic and will change, this is just an example) $string = 'value="<p>Some text</p> <a href="#">linky</a>"'; // Run the match and spit out the results preg_match_all('/([^"]*)(?:\s*=\s*(\042|\047))([^"]*)/is', $string , $results); // Here is the array I want to end up with Array ( [0] => Array ( [0] => value="<p>Some text</p><a href="#">linky</a>" ) [1] => Array ( [0] => value ) [2] => Array ( [0] => " ) [3] => Array ( [0] => <p>Some text</p><a href="#">linky</a> ) ) Basically the double quotes on the link are causing me some trouble so my first though was to do [^"]$ or something to have it just run until the last double quote, but that isn't getting me anywhere. Another idea I had was maybe process the string in PHP to strip out any inner quotes, but i'm not sure ho to go about this either. Hopefully I'm being clear, it is pretty late and i've been at this far too long!

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• std::vector optimisation required

  - by marcp

  I've written a routine that uses std::vector<double> rather heavily. It runs rather slowly and AQTime seems to imply that I am constructing mountains of vectors but I'm not sure why I would be. For some context, my sample run iterates 10 times. Each iteration copies 3 c arrays of ~400 points into vectors and creates 3 new same sized vectors for output. Each output point might be the result of summing up to 20 points from 2 of the input vectors, which works out to a worst case of 10*400*3*2*20 = 480,000 dereferences. Incredibly the profiler indicates that some of the std:: methods are being called 46 MILLION times. I suspect I'm doing something wrong! Some code: vector<double>gdbChannel::GetVector() { if (fHaveDoubleData & (fLength > 0)) { double * pD = getDoublePointer(); vector<double>v(pD, pD + fLength); return v; } else { throw(Exception("attempt to retrieve vector on empty line")); ; } } void gdbChannel::SaveVector(GX_HANDLE _hLine, const vector<double> & V) { if (hLine != _hLine) { GetLine(_hLine, V.size(), true); } GX_DOUBLE * pData = getDoublePointer(); memcpy(pData, &V[0], V.size()*sizeof(V[0])); ReplaceData(); } ///This routine gets called 10 times bool SpecRatio::DoWork(GX_HANDLE_PTR pLine) { if (!(hKin.GetLine(*pLine, true) && hUin.GetLine(*pLine, true) && hTHin.GetLine(*pLine, true))) { return true; } vector<double>vK = hKin.GetVector(); vector<double>vU = hUin.GetVector(); vector<double>vTh = hTHin.GetVector(); if ((vK.size() == 0) || (vU.size() == 0) || (vTh.size() == 0)) { return true; } ///TODO: confirm all vectors the same lenghth len = vK.size(); vUK.clear(); // these 3 vectors are declared as private class members vUTh.clear(); vThK.clear(); vUK.reserve(len); vUTh.reserve(len); vThK.reserve(len); // TODO: ensure everything is same fidincr, fidstart and length for (int i = 0; i < len; i++) { if (vK.at(i) < MinK) { vUK.push_back(rDUMMY); vUTh.push_back(rDUMMY); vThK.push_back(rDUMMY); } else { vUK.push_back(RatioPoint(vU, vK, i, UMin, KMin)); vUTh.push_back(RatioPoint(vU, vTh, i, UMin, ThMin)); vThK.push_back(RatioPoint(vTh, vK, i, ThMin, KMin)); } } hUKout.setFidParams(hKin); hUKout.SaveVector(*pLine, vUK); hUTHout.setFidParams(hKin); hUTHout.SaveVector(*pLine, vUTh); hTHKout.setFidParams(hKin); hTHKout.SaveVector(*pLine, vThK); return TestError(); } double SpecRatio::VValue(vector<double>V, int Index) { double result; if ((Index < 0) || (Index >= len)) { result = 0; } else { try { result = V.at(Index); if (OasisUtils::isDummy(result)) { result = 0; } } catch (out_of_range) { result = 0; } } return result; } double SpecRatio::RatioPoint(vector<double>Num, vector<double>Denom, int Index, double NumMin, double DenomMin) { double num = VValue(Num, Index); double denom = VValue(Denom, Index); int s = 0; // Search equalled 10 in this case while (((num < NumMin) || (denom < DenomMin)) && (s < Search)) { num += VValue(Num, Index - s) + VValue(Num, Index + s); denom += VValue(Denom, Index - s) + VValue(Denom, Index + s); s++; } if ((num < NumMin) || (denom < DenomMin)) { return rDUMMY; } else { return num / denom; } } The top AQTime offenders are: std::_Uninit_copy , double *, std::allocator 3.65 secs and 115731 Hits std::_Construct 1.69 secs and 46450637 Hits std::_Vector_const_iterator ::operator !=1.66 secs and 46566395 Hits and so on... std::allocator<double>::construct, operator new, std::_Vector_const_iterator<double, std::allocator<double> >::operator ++, std::_Vector_const_iterator<double, std::allocator<double> >::operator * std::_Vector_const_iterator<double, std::allocator<double> >::operator == each get called over 46 million times. I'm obviously doing something wrong to cause all these objects to be created. Can anyone see my error(s)?

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• C# error casting from double to int32

  - by orfix

  using NUF = NUnit.Framework; [NUF.Test]public void DifferentCastingTest() { NUF.Assert.That((int)0.499999D, NUF.Is.EqualTo(0)); NUF.Assert.That((int)0.500000D, NUF.Is.EqualTo(0)); // !!! row 1 NUF.Assert.That((int)1.499999D, NUF.Is.EqualTo(1)); NUF.Assert.That((int)1.500000D, NUF.Is.EqualTo(1)); // !!! row 2 NUF.Assert.That(System.Convert.ToInt32(0.499999D), NUF.Is.EqualTo(0)); NUF.Assert.That(System.Convert.ToInt32(0.500000D), NUF.Is.EqualTo(0)); // !!! NUF.Assert.That(System.Convert.ToInt32(1.499999D), NUF.Is.EqualTo(1)); NUF.Assert.That(System.Convert.ToInt32(1.500000D), NUF.Is.EqualTo(2)); //!!! row 3 } The same double value (1.5D) is converted in different way by casting and Convert.ToInt32 (see row 2 and 3), and two double with same mantissa (0.5 and 1.5) is rounded in different mode (see row 1 and 2). Is it a bug?

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• Double join with habtm in ActiveRecord

  - by Daniel Huckstep

  I have a weird situation involving the need of a double inner join. I have tried the query I need, I just don't know how to make rails do it. The Data Account (has_many :sites) Site (habtm :users, belongs_to :account) User (habtm :sites) Ignore that they are habtm or whatever, I can make them habtm or has_many :through. I want to be able to do @user.accounts or @account.users Then of course I should be able to do @user.accounts < @some_other_account And then have @user.sites include all the sites from @some_other_account. I've fiddled with habtm and has_many :through but can't get it to do what I want. Basically I need to end up with a query like this (copied from phpmyadmin. Tested and works): SELECT accounts.* FROM accounts INNER JOIN sites ON sites.account_id = accounts.id INNER JOIN user_sites ON sites.id = user_sites.site_id WHERE user_sites.user_id = 2 Can I do this? Is it even a good idea to have this double join? I am assuming it would work better if users had the association with accounts to begin with, and then worry about getting @user.sites instead, but it works better for many other things if it is kept the way it is (users <- sites).

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• Official names for pointer operators

  - by FredOverflow

  What are the official names for the operators * and & in the context of pointers? They seem to be frequently called dereference operator and address-of operator respectively, but unfortunately, the section on unary operators in the standard does not name them. I really don't want to name & address-of anymore, because & returns a pointer, not an address. (A pointer is a language mechanism, while an address is an implementation detail. Addresses are untyped, while pointers aren't, except for void*.) The standard is very clear about this: The result of the unary & operator is a pointer to its operand. Symmetry suggests to name & reference operator which is a little unfortunate because of the collision with references in C++. The fact that & returns a pointer suggests pointer operator. Are there any official sources that would confirm these (or other) namings?

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• How to tell endianness from this output?

  - by Nick Rosencrantz

  I'm running this example program and I'm suppossed to be able to tell from the output what machine type it is. I'm certain it's from inspecting one or two values but how should I perform this inspection? /* pointers.c - Test pointers * Written 2012 by F Lundevall * Copyright abandoned. This file is in the public domain. * * To make this program work on as many systems as possible, * addresses are converted to unsigned long when printed. * The 'l' in formatting-codes %ld and %lx means a long operand. */ #include <stdio.h> #include <stdlib.h> int * ip; /* Declare a pointer to int, a.k.a. int pointer. */ char * cp; /* Pointer to char, a.k.a. char pointer. */ /* Declare fp as a pointer to function, where that function * has one parameter of type int and returns an int. * Use cdecl to get the syntax right, http://cdecl.org/ */ int ( *fp )( int ); int val1 = 111111; int val2 = 222222; int ia[ 17 ]; /* Declare an array of 17 ints, numbered 0 through 16. */ char ca[ 17 ]; /* Declare an array of 17 chars. */ int fun( int parm ) { printf( "Function fun called with parameter %d\n", parm ); return( parm + 1 ); } /* Main function. */ int main() { printf( "Message PT.01 from pointers.c: Hello, pointy World!\n" ); /* Do some assignments. */ ip = &val1; cp = &val2; /* The compiler should warn you about this. */ fp = fun; ia[ 0 ] = 11; /* First element. */ ia[ 1 ] = 17; ia[ 2 ] = 3; ia[ 16 ] = 58; /* Last element. */ ca[ 0 ] = 11; /* First element. */ ca[ 1 ] = 17; ca[ 2 ] = 3; ca[ 16 ] = 58; /* Last element. */ printf( "PT.02: val1: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &val1, val1, val1 ); printf( "PT.03: val2: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &val2, val2, val2 ); printf( "PT.04: ip: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &ip, (long) ip, (long) ip ); printf( "PT.05: Dereference pointer ip and we find: %d \n", *ip ); printf( "PT.06: cp: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &cp, (long) cp, (long) cp ); printf( "PT.07: Dereference pointer cp and we find: %d \n", *cp ); *ip = 1234; printf( "\nPT.08: Executed *ip = 1234; \n" ); printf( "PT.09: val1: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &val1, val1, val1 ); printf( "PT.10: ip: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &ip, (long) ip, (long) ip ); printf( "PT.11: Dereference pointer ip and we find: %d \n", *ip ); printf( "PT.12: val1: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &val1, val1, val1 ); *cp = 1234; /* The compiler should warn you about this. */ printf( "\nPT.13: Executed *cp = 1234; \n" ); printf( "PT.14: val2: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &val2, val2, val2 ); printf( "PT.15: cp: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &cp, (long) cp, (long) cp ); printf( "PT.16: Dereference pointer cp and we find: %d \n", *cp ); printf( "PT.17: val2: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &val2, val2, val2 ); ip = ia; printf( "\nPT.18: Executed ip = ia; \n" ); printf( "PT.19: ia[0]: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &ia[0], ia[0], ia[0] ); printf( "PT.20: ia[1]: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &ia[1], ia[1], ia[1] ); printf( "PT.21: ip: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &ip, (long) ip, (long) ip ); printf( "PT.22: Dereference pointer ip and we find: %d \n", *ip ); ip = ip + 1; /* add 1 to pointer */ printf( "\nPT.23: Executed ip = ip + 1; \n" ); printf( "PT.24: ip: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &ip, (long) ip, (long) ip ); printf( "PT.25: Dereference pointer ip and we find: %d \n", *ip ); cp = ca; printf( "\nPT.26: Executed cp = ca; \n" ); printf( "PT.27: ca[0]: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &ca[0], ca[0], ca[0] ); printf( "PT.28: ca[1]: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &ca[1], ca[1], ca[1] ); printf( "PT.29: cp: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &cp, (long) cp, (long) cp ); printf( "PT.30: Dereference pointer cp and we find: %d \n", *cp ); cp = cp + 1; /* add 1 to pointer */ printf( "\nPT.31: Executed cp = cp + 1; \n" ); printf( "PT.32: cp: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &cp, (long) cp, (long) cp ); printf( "PT.33: Dereference pointer cp and we find: %d \n", *cp ); ip = ca; /* The compiler should warn you about this. */ printf( "\nPT.34: Executed ip = ca; \n" ); printf( "PT.35: ca[0]: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &ca[0], ca[0], ca[0] ); printf( "PT.36: ca[1]: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &ca[1], ca[1], ca[1] ); printf( "PT.37: ip: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &ip, (long) ip, (long) ip ); printf( "PT.38: Dereference pointer ip and we find: %d \n", *ip ); cp = ia; /* The compiler should warn you about this. */ printf( "\nPT.39: Executed cp = ia; \n" ); printf( "PT.40: cp: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &cp, (long) cp, (long) cp ); printf( "PT.41: Dereference pointer cp and we find: %d \n", *cp ); printf( "\nPT.42: fp: stored at %lx (hex); value is %ld (dec), %lx (hex)\n", (long) &fp, (long) fp, (long) fp ); printf( "PT.43: Dereference fp and see what happens.\n" ); val1 = (*fp)(42); printf( "PT.44: Executed val1 = (*fp)(42); \n" ); printf( "PT.45: val1: stored at %lx (hex); value is %d (dec), %x (hex)\n", (long) &val1, val1, val1 ); return( 0 ); } Output Message PT.01 from pointers.c: Hello, pointy World! PT.02: val1: stored at 21e50 (hex); value is 111111 (dec), 1b207 (hex) PT.03: val2: stored at 21e54 (hex); value is 222222 (dec), 3640e (hex) PT.04: ip: stored at 21eb8 (hex); value is 138832 (dec), 21e50 (hex) PT.05: Dereference pointer ip and we find: 111111 PT.06: cp: stored at 21e6c (hex); value is 138836 (dec), 21e54 (hex) PT.07: Dereference pointer cp and we find: 0 PT.08: Executed *ip = 1234; PT.09: val1: stored at 21e50 (hex); value is 1234 (dec), 4d2 (hex) PT.10: ip: stored at 21eb8 (hex); value is 138832 (dec), 21e50 (hex) PT.11: Dereference pointer ip and we find: 1234 PT.12: val1: stored at 21e50 (hex); value is 1234 (dec), 4d2 (hex) PT.13: Executed *cp = 1234; PT.14: val2: stored at 21e54 (hex); value is -771529714 (dec), d203640e (hex) PT.15: cp: stored at 21e6c (hex); value is 138836 (dec), 21e54 (hex) PT.16: Dereference pointer cp and we find: -46 PT.17: val2: stored at 21e54 (hex); value is -771529714 (dec), d203640e (hex) PT.18: Executed ip = ia; PT.19: ia[0]: stored at 21e74 (hex); value is 11 (dec), b (hex) PT.20: ia[1]: stored at 21e78 (hex); value is 17 (dec), 11 (hex) PT.21: ip: stored at 21eb8 (hex); value is 138868 (dec), 21e74 (hex) PT.22: Dereference pointer ip and we find: 11 PT.23: Executed ip = ip + 1; PT.24: ip: stored at 21eb8 (hex); value is 138872 (dec), 21e78 (hex) PT.25: Dereference pointer ip and we find: 17 PT.26: Executed cp = ca; PT.27: ca[0]: stored at 21e58 (hex); value is 11 (dec), b (hex) PT.28: ca[1]: stored at 21e59 (hex); value is 17 (dec), 11 (hex) PT.29: cp: stored at 21e6c (hex); value is 138840 (dec), 21e58 (hex) PT.30: Dereference pointer cp and we find: 11 PT.31: Executed cp = cp + 1; PT.32: cp: stored at 21e6c (hex); value is 138841 (dec), 21e59 (hex) PT.33: Dereference pointer cp and we find: 17 PT.34: Executed ip = ca; PT.35: ca[0]: stored at 21e58 (hex); value is 11 (dec), b (hex) PT.36: ca[1]: stored at 21e59 (hex); value is 17 (dec), 11 (hex) PT.37: ip: stored at 21eb8 (hex); value is 138840 (dec), 21e58 (hex) PT.38: Dereference pointer ip and we find: 185664256 PT.39: Executed cp = ia; PT.40: cp: stored at 21e6c (hex); value is 138868 (dec), 21e74 (hex) PT.41: Dereference pointer cp and we find: 0 PT.42: fp: stored at 21e70 (hex); value is 69288 (dec), 10ea8 (hex) PT.43: Dereference fp and see what happens. Function fun called with parameter 42 PT.44: Executed val1 = (*fp)(42); PT.45: val1: stored at 21e50 (hex); value is 43 (dec), 2b (hex)

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• dynamically created arrays

  - by DevAno1

  My task consists of two parts. First I have to create globbal char array of 100 elements, and insert some text to it using cin. Afterwards calculate amount of chars, and create dedicated array with the length of the inputted text. I was thinking about following solution : char[100]inputData; int main() { cin >> inputData >> endl; int length=0; for(int i=0; i<100; i++) { while(inputData[i] == "\0") { ++count; } } char c = new char[count]; Am I thinking good ? Second part of the task is to introduce in the first program dynamically created array of pointers to all inserted words. Adding a new word should print all the previous words and if there is no space for next words, size of the inputData array should be increased twice. And to be honest this is a bit too much for me. How I can create pointers to words specifically ? And how can I increase the size of global array without loosing its content ? With some temporary array ?

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• Polymorphic Queue

  - by metdos

  Hello Everyone, I'm trying to implement a Polymorphic Queue. Here is my trial: QQueue <Request *> requests; while(...) { QString line = QString::fromUtf8(client->readLine()).trimmed(); if(...)){ Request *request=new Request(); request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); //this initialize variables in request using tcpMessage if(request->requestType==REQUEST_LOGIN){ LoginRequest loginRequest; request=&loginRequest; request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); requests.enqueue(request); } //Here pointers in "requests" do not point to objects I created above, and I noticed that their destructors are also called. LoginRequest *loginRequest2=dynamic_cast<LoginRequest *>(requests.dequeue()); loginRequest2->decodeFromTcpMessage(); } } Unfortunately, I could not manage to make work Polymorphic Queue with this code because of the reason I mentioned in second comment.I guess, I need to use smart-pointers, but how? I'm open to any improvement of my code or a new implementation of polymorphic queue. Thanks.

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• Does it exist: smart pointer, owned by one object allowing access.

  - by Noah Roberts

  I'm wondering if anyone's run across anything that exists which would fill this need. Object A contains an object B. It wants to provide access to that B to clients through a pointer (maybe there's the option it could be 0, or maybe the clients need to be copiable and yet hold references...whatever). Clients, lets call them object C, would normally, if we're perfect developers, be written carefully so as to not violate the lifetime semantics of any pointer to B they might have...but we're not perfect, in fact we're pretty dumb half the time. So what we want is for object C to have a pointer to object B that is not "shared" ownership but that is smart enough to recognize a situation in which the pointer is no longer valid, such as when object A is destroyed or it destroys object B. Accessing this pointer when it's no longer valid would cause an assertion/exception/whatever. In other words, I wish to share access to data in a safe, clear way but retain the original ownership semantics. Currently, because I've not been able to find any shared pointer in which one of the objects owns it, I've been using shared_ptr in place of having such a thing. But I want clear owneship and shared/weak pointer doesn't really provide that. Would be nice further if this smart pointer could be attached to member variables and not just hold pointers to dynamically allocated memory regions. If it doesn't exist I'm going to make it, so I first want to know if someone's already released something out there that does it. And, BTW, I do realize that things like references and pointers do provide this sort of thing...I'm looking for something smarter.

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• Isn't an Iterator in c++ a kind of a pointer?

  - by Bilthon

  Ok this time I decided to make a list using the STL. I need to create a dedicated TCP socket for each client. So everytime I've got a connection, I instantiate a socket and add a pointer to it on a list. list<MyTcp*> SocketList; //This is the list of pointers to sockets list<MyTcp*>::iterator it; //An iterator to the list of pointers to TCP sockets. Putting a new pointer to a socket was easy, but now every time the connection ends I should disconnect the socket and delete the pointer so I don't get a huge memory leak, right? well.. I thought I was doing ok by setting this: it=SocketList.begin(); while( it != SocketList.end() ){ if((*it)->getClientId() == id){ pSocket = it; // <-------------- compiler complains at this line SocketList.remove(pSocket); pSocket->Disconnect(); delete pSocket; break; } } But the compiler is saying this: error: invalid cast from type ‘std::_List_iterator<MyTcp*>’ to type ‘MyTcp*’ Can someone help me here? i thought I was doing things right, isn't an iterator at any given time just pointing to one of the elements of the set? how can I fix it?

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