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• Debugging unexpected error message - possible memory management problem?

  - by Ben Packard

  I am trying to debug an application that is throwing up strange (to my untutored eyed) errors. When I try to simply log the count of an array... NSLog(@"Array has %i items", [[self startingPlayers] count]); ...I sometimes get an error: -[NSCFString count]: unrecognized selector sent to instance 0x1002af600 or other times -[NSConcreteNotification count]: unrecognized selector sent to instance 0x1002af600 I am not sending 'count' to any NSString or NSNotification, and this line of code works fine normally. A Theory... Although the error varies, the crash happens at predictable times, immediately after I have run through some other code where I'm thinking I might have a memory management issue. Is it possible that the object reference is still pointing to something that is meant to be destroyed? Sorry if my terms are off, but perhaps it's expecting the array at the address it calls 'count' on, but finds another previous object that shouldn't still be there (eg an NSString)? Would this cause the problem? If so, what is the most efficient way to debug and find out what is that address? Most of my debugging up until now involves inserting NSLogs, so this would be a good opportunity to learn how to use the debugger.

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• Template class giving linker error ...

  - by Atul

  Hi, I am having a template class which is exposed, in which I added a method. This class is in namespace A. Now, I am calling this method in another namespace (say B). Initially, compiler gave me linker error saying "unresolved external symbol" for this particular method. However, if I call this method inside the same namespace (that is A), it links well. After that, it links well in namespace B as well. Why could this be happening ? Does this has something to do with the creating Template object of my class ? Atul

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• "Inherited" types using CRTP and typedef

  - by Ken Moynihan

  The following code does not compile. I get an error message: error C2039: 'Asub' : is not a member of 'C' Can someone help me to understand this? Tried VS2008 & 2010 compiler. template <class T> class B { typedef int Asub; public: void DoSomething(typename T::Asub it) { } }; class C : public B<C> { public: typedef int Asub; }; class A { public: typedef int Asub; }; int _tmain(int argc, _TCHAR* argv[]) { C theThing; theThing.DoSomething(C::Asub()); return 0; }

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• GCC ICE -- alternative function syntax, variadic templates and tuples

  - by Marc H.

  (Related to C++0x, How do I expand a tuple into variadic template function arguments?.) The following code (see below) is taken from this discussion. The objective is to apply a function to a tuple. I simplified the template parameters and modified the code to allow for a return value of generic type. While the original code compiles fine, when I try to compile the modified code with GCC 4.4.3, g++ -std=c++0x main.cc -o main GCC reports an internal compiler error (ICE) with the following message: main.cc: In function ‘int main()’: main.cc:53: internal compiler error: in tsubst_copy, at cp/pt.c:10077 Please submit a full bug report, with preprocessed source if appropriate. See <file:///usr/share/doc/gcc-4.4/README.Bugs> for instructions. Question: Is the code correct? or is the ICE triggered by illegal code? // file: main.cc #include <tuple> // Recursive case template<unsigned int N> struct Apply_aux { template<typename F, typename T, typename... X> static auto apply(F f, const T& t, X... x) -> decltype(Apply_aux<N-1>::apply(f, t, std::get<N-1>(t), x...)) { return Apply_aux<N-1>::apply(f, t, std::get<N-1>(t), x...); } }; // Terminal case template<> struct Apply_aux<0> { template<typename F, typename T, typename... X> static auto apply(F f, const T&, X... x) -> decltype(f(x...)) { return f(x...); } }; // Actual apply function template<typename F, typename T> auto apply(F f, const T& t) -> decltype(Apply_aux<std::tuple_size<T>::value>::apply(f, t)) { return Apply_aux<std::tuple_size<T>::value>::apply(f, t); } // Testing #include <string> #include <iostream> int f(int p1, double p2, std::string p3) { std::cout << "int=" << p1 << ", double=" << p2 << ", string=" << p3 << std::endl; return 1; } int g(int p1, std::string p2) { std::cout << "int=" << p1 << ", string=" << p2 << std::endl; return 2; } int main() { std::tuple<int, double, char const*> tup(1, 2.0, "xxx"); std::cout << apply(f, tup) << std::endl; std::cout << apply(g, std::make_tuple(4, "yyy")) << std::endl; } Remark: If I hardcode the return type in the recursive case (see code), then everything is fine. That is, substituting this snippet for the recursive case does not trigger the ICE: // Recursive case (hardcoded return type) template<unsigned int N> struct Apply_aux { template<typename F, typename T, typename... X> static int apply(F f, const T& t, X... x) { return Apply_aux<N-1>::apply(f, t, std::get<N-1>(t), x...); } }; Alas, this is an incomplete solution to the original problem.

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• How to make safe cast using generics in C#?

  - by TN

  I want to implement a generic method on a generic class which would allow to cast safely, see example: public class Foo<T> : IEnumerable<T> { ... public IEnumerable<R> SafeCast<R>() where T : R { return this.Select(item => (R)item); } } However, the compiler tells me that Foo<T>.SafeCast<R>() does not define parameter 'T'. I understand this message that I cannot specify a constraint on T in the method since it is not defined in the method. But how can I specify an inverse constraint?

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• How to restrain one's self from the overwhelming urge to rewrite everything?

  - by Scott Saad

  Setup Have you ever had the experience of going into a piece of code to make a seemingly simple change and then realizing that you've just stepped into a wasteland that deserves some serious attention? This usually gets followed up with an official FREAK OUT moment, where the overwhelming feeling of rewriting everything in sight starts to creep up. It's important to note that this bad code does not necessarily come from others as it may indeed be something we've written or contributed to in the past. Problem It's obvious that there is some serious code rot, horrible architecture, etc. that needs to be dealt with. The real problem, as it relates to this question, is that it's not the right time to rewrite the code. There could be many reasons for this: Currently in the middle of a release cycle, therefore any changes should be minimal. It's 2:00 AM in the morning, and the brain is starting to shut down. It could have seemingly adverse affects on the schedule. The rabbit hole could go much deeper than our eyes are able to see at this time. etc... Question So how should we balance the duty of continuously improving the code, while also being a responsible developer? How do we refrain from contributing to the broken window theory, while also being aware of actions and the potential recklessness they may cause? Update Great answers! For the most part, there seems to be two schools of thought: Don't resist the urge as it's a good one to have. Don't give in to the temptation as it will burn you to the ground. It would be interesting to know if more people feel any balance exists.

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• Using Library files in Linux

  - by paultop6

  Hi Guys, Im trying to use some of the functions that are in the /lib/libproc-3.2.6.so library in my Ubuntu Distribution. I have downloaded and installed the header files and they are defined in my source files. Currently this is all im trying to do, just for starters... proc_t **read_proc = readproctab(0); But i get the following compiler error: /tmp/cclqMImG.o: In function `Sysmon::initialise_sysmon()': sysmon.cpp:(.text+0x494): undefined reference to `readproctab' collect2: ld returned 1 exit status Im aware im probably doing some wrong with the command im using to compile it, but due to lack of experience im not sure what im doign wrong. This is the g++ command im using to compile my cpp file: g++ -o sysmon.o sysmon.cpp `pkg-config --libs --cflags gtk+-2.0` Can someone please give me some pointers as to where im going wrong Regards Paul

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• When using the getInstance() method of the abstract java.text.NumberFormat class, what is the actual

  - by iamchuckb

  This question expands upon the one at abstract-class-numberformat-very-confused-about-getinstance. I feel that this question is different enough to merit being asked on its own. In the answers to that question, it was stated that a code statement such as NumberFormat en = NumberFormat.getInstance(Locale.US); returns an object that is a subclass of the java.text.NumberFormat class. It makes sense to me why the return type can't be just an instance of NumberFormat since that is an abstract class. Rather, it was stated that the returned object is at least an instance of NumberFormat, but actually something else. My question is this: what specifically is the class of the object that is returned? In the Sun documentation the only subclasses I see are ChoicesFormat and DecimalFormat. Is there some sort of behind the scenes compiler voodoo going on here? Thanks in advance!

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• Boost Regex throwing an error

  - by Srinivasa Varadan

  Hi ALL, I have the following error when I try to compile my code in g+ compiler using eclipse In function `ZSt19__iterator_categoryIPKSsENSt15iterator_traitsIT_E17iterator_categoryERKS3_': C:/Program Files (x86)/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_algobase.h:(.text$_ZN5boost11basic_regexIcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEE6assignEPKcS7_j[boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::assign(char const*, char const*, unsigned int)]+0x22): undefined reference to `boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::do_assign(char const*, char const*, unsigned int)' collect2: ld returned 1 exit status Build error occurred, build is stopped All I have done is this statement boost::regex re("\s+"); along with the header #inlucde Could you kindly tell me how to proceed ?

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• FxCop giving a warning on private constructor CA1823 and CA1053

  - by Luis Sánchez

  I have a class that looks like the following: Public Class Utilities Public Shared Function blah(userCode As String) As String 'doing some stuff End Function End Class I'm running FxCop 10 on it and it says: "Because type 'Utilities' contains only 'static' ( 'Shared' in Visual Basic) members, add a default private constructor to prevent the compiler from adding a default public constructor." Ok, you're right Mr. FxCop, I'll add a private constructor: Private Utilities() Now I'm having: "It appears that field 'Utilities.Utilities' is never used or is only ever assigned to. Use this field or remove it." Any ideas of what should I do to get rid of both warnings?

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• Debugging a release version of a DLL (with PDB file)

  - by Martin

  If I have a DLL (that was built in release-mode) and the corresponding PDB file, is it possible to debug (step-into) classes/methods contained in that DLL? If so, what are the required steps/configuration (e.g. where to put the PDB file)? Edit: If have the PDB file in the same place as the DLL (in the bin/debug directory of a simple console test application). I can see that the symbols for the DLL are loaded (in the Output window and also in the Modules window), but still I cannot step into the methods of that DLL. Could this be the result of compiler optimizations (as described by Michael in his answer)?

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• C1083 : Permission denied on .sbr files

  - by speps

  Hello, I am using Visual Studio 2005 (with SP1) and I am getting weird errors concerning .sbr files. These files, as I read on MSDN, are intermediate files for BSCMAKE to generate a .bsc file. The errors I get are, for example (on different builds) : 11string.cpp : fatal error C1083: Impossible d'ouvrir le fichier généré(e) par le compilateur : '.\debug\String.sbr' : Permission denied 58type.cpp : fatal error C1083: Impossible d'ouvrir le fichier généré(e) par le compilateur : '.\Debug/Type.sbr' : Permission denied Translation : cannot open compiler intermediate file It seems to be consistent (I have at least 5 or 6 examples like this) with a .cpp file being compiled twice in the same project, respectively : 11String.cpp *some warnings, 2 lines* 11String.cpp 58Type.cpp *some warnings and other files compiled, a lot of lines* 58Type.cpp I already checked the .vcproj files for duplicate entries and it does not seem to be the problem. I would appreciate any help regarding this issue. Deactivating the build of .bsc files seems to be a workaround but maybe someone has better information than this. Thanks.

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• Flipping View transition becomes clunky when using UIPickerViews with a large number of elements

  - by user302246

  I have a very simple app created with the Utility Application project template on XCode. My MainView has two UIPickerView components and two buttons. The FlipSideView has another UIPickerView. The pickers on the main view each have 4 segments and each segment has 8 rows. The picker on the flip side has just 1 segment with 8 rows. All rows on all pickers are just text. With just this setup, pressing the button to flip the view back and forth displays a noticeable delay before the animation actually starts, and then the animation actually seems to go faster than what it should, like it's trying to make up for the lost time. I removed the pickers in interface builder and loaded the app on the phone and the animation now seems natural. I also tried just one picker (the flipside one) and things still seem normal. So my current theory is that the number of objects involved in the main view is the cause. The thing is that I don't think it's that many (4 x 8 x 2 = 64), but I could be completely wrong. This is pretty much my first app so maybe I'm just doing something grossly wrong, or maybe the phone is has a lot more limited processing than I thought. I am thinking of creating the picker views with pickerView:viewForRow:forComponent:reusingView: to see if this hopefully performs better, but I'm not sure if this is just a waste of time. Any suggestions? Thanks Ruy P.S.: Testing on a 3G phone on 3.1.2

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• msvcrt: memory usage goes wild, but not under debugger

  - by al_miro

  I have a C++ code compiled with Intel compiler, 32bit, in MS VC6 mode, so using either msvcrt.dll or msvcrtd.dll. The process makes heavy memory allocation and deallocation. I monitor the memory usage with WMI and look at VirtualSize and WorkingSetSize. with debug runtime (msvcrtd.dll): virtual constant 1.7GB, working constant 1.2GB with non-debug runtime (msvcrt.dll): virtual raising 1.7-- 2.1GB, working raising 1.2-1.4GB with non-debug runtime but under debugger (windbg): virtual constant 1.7GB, working constant At 2.1 GB virtual the process is crashing (as expected). But why would the virtual usage increase only with (non-debug) msvcrt.dll and only if not under debugger? In all cases compilation flags are identical, only runtime libs are different.

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• Using typedefs from a template class in a template (non-member) function

  - by atomicpirate

  The following fails to compile (with gcc 4.2.1 on Linux, anyway): template< typename T > class Foo { public: typedef int FooType; }; void ordinary() { Foo< int >::FooType bar = 0; } template< typename T > void templated() { Foo< T >::FooType bar = T( 0 ); } int main( int argc, char **argv ) { return 0; } The problem is with this line: Foo< T >::FooType bar = 0; ...and the compiler makes this complaint: foo.c: In function ‘void templated()’: foo.c:22: error: expected `;' before ‘bar’ Normally one sees this when a type hasn't been declared, but as far as I can tell, Foo< T ::FooType should be perfectly valid inside templated().

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• Why do my MIPS crosscompiler works like this for NOT operation?

  - by Mazicky

  Hello, I setup my crosscompiler for making MIPS instructions. And it compiles C code well. but I found a weird thing for NOT operations. if i make code like int a; func(!a); and i studied MIPS instructions with text book that says "MIPS converts NOT operation to 'nor with zero'" So i thought it would converted like nor a a $zero but my compiler converts xori a a 0x0 sltu a 1 /////////////////////////////////////// i compiled the code with 'myaccount mipsel-unknown-linux-gnu-gcc -S myfilename.c' and it makes myfilename.s file.. what am i missing??

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• "Cannot convert to IComparer"

  - by Odrade

  I have the following IComparer defined for boxed RegistryItem objects: public class BoxedRegistryItemComparer : IComparer<object> { public int Compare(object left, object right) { RegistryItem leftReg = (RegistryItem)left; RegistryItem rightReg = (RegistryItem)right; return string.Compare(leftReg.Name, rightReg.Name); } } I want to use this to sort an ArrayList of boxed RegistryItems (It really should be a List<RegistryItem, but that's out of my control). ArrayList regItems = new ArrayList(); // fill up the list ... BoxedRegistryItemComparer comparer = new BoxedRegistryItemComparer(); ArrayList.sort(comparer); However, the last line gives the compiler error: "Cannot convert from BoxedRegistryItemComparer to System.Collections.IComparer". I would appreciate it if someone could point out my mistake.

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• Best design for generating code from an AST?

  - by Sam Washburn

  I'm working on a pretty complex DSL that I want to compile down into a few high level languages. The whole process has been a learning experience. The compiler is written in java. I was wondering if anyone knew a best practice for the design of the code generator portion. I currently have everything parsed into an abstract syntax tree. I was thinking of using a template system, but I haven't researched that direction too far yet as I would like to hear some wisdom first from stack overflow. Thanks!

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• Documentation concerning platform-specific macros in Linux/POSIX

  - by Nubok

  When compiling a C/C++ program under Windows using Visual Studio (or a compiler that tries to be compatible) there is a predefined macro _WIN32 (Source: http://msdn.microsoft.com/en-us/library/b0084kay.aspx) that you can use for platform-specific #ifdef-s. What I am looking for is an analogon under Linux: a macro which tells me that I am compiling for Linux/an OS that claims to be (more or less) POSIX-compatible. So I looked into gcc documentation and found this: http://gcc.gnu.org/onlinedocs/cpp/System_002dspecific-Predefined-Macros.html Applied to my program, the following macros (gcc 4.4.5 - Ubuntu 10.10) looked promising (I hope that I didn't drop an important macro): #define __USE_BSD 1 #define __unix__ 1 #define __linux 1 #define __unix 1 #define __linux__ 1 #define _POSIX_SOURCE 1 #define __STDC_HOSTED__ 1 #define __STDC_IEC_559__ 1 #define __gnu_linux__ 1 #define __USE_SVID 1 #define __USE_XOPEN2K 1 #define __USE_POSIX199506 1 #define _G_USING_THUNKS 1 #define __USE_XOPEN2K8 1 #define _BSD_SOURCE 1 #define unix 1 #define linux 1 #define __USE_POSIX 1 #define __USE_POSIX199309 1 #define __SSP__ 1 #define _SVID_SOURCE 1 #define _G_HAVE_SYS_CDEFS 1 #define __USE_POSIX_IMPLICITLY 1 Where do I find a detailed documentation of them - as to the mentioned Windows-specific macros above? Additionally I'd be interested in macros normally defined for other POSIX-compliant operating systems as *BSD etc.

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• Ambiguous Generic restriction T:class vs T:struct

  - by Maslow

  This code generates a compiler error that the member is already defined with the same parameter types. private T GetProperty<T>(Func<Settings, T> GetFunc) where T:class { try { return GetFunc(Properties.Settings.Default); } catch (Exception exception) { SettingReadException(this,exception); return null; } } private TNullable? GetProperty<TNullable>(Func<Settings, TNullable> GetFunc) where TNullable : struct { try { return GetFunc(Properties.Settings.Default); } catch (Exception ex) { SettingReadException(this, ex); return new Nullable<TNullable>(); } } Is there a clean work around?

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• Error when using --static option with macrubyc

  - by Jakub Hampl

  I want to create a binary executable for a relatively simple script that would not require people to install macruby or HotCocoa. The script is here. I've understood that I want to use the --static option for the compiler and I'm using the following command: macrubyc -o postprocessor --static postprocessor.rb I get the following error: ld: library not found for -lLLVMBitWriter collect2: ld returned 1 exit status Error when executing `/usr/bin/g++ -o "postprocessor" -arch x86_64 -L/Library/Frameworks/MacRuby.framework/Versions/0.6/usr/lib -lmacruby-static -L/usr/local/lib -lpthread -lffi -lm -lLLVMBitWriter -lLLVMX86CodeGen -lLLVMX86Info -lLLVMSelectionDAG -lLLVMAsmPrinter -lLLVMJIT -lLLVMExecutionEngine -lLLVMCodeGen -lLLVMScalarOpts -lLLVMTransformUtils -lLLVMipa -lLLVMAnalysis -lLLVMTarget -lLLVMMC -lLLVMCore -lLLVMSupport -lLLVMSystem -lpthread -ldl -lxml2 -lobjc -lauto -licucore -framework Foundation "/var/folders/wU/wUGgoG1JGeKBgwalWLPMAU+++TI/-Tmp-/main-72203.o" "./postprocessor.o"' What should I do to get this running?

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• error C2440: '=' : cannot convert from 'std::string []' to 'std::string []'

  - by Bach

  now what is wrong with this code! Header: #pragma once #include <string> using namespace std; class Menu { public: Menu(string []); ~Menu(void); }; Implementation: #include "Menu.h" string _choices[]; Menu::Menu(string items[]) { _choices = items; } Menu::~Menu(void) { } compiler is complaining: error C2440: '=' : cannot convert from 'std::string []' to 'std::string []' There are no conversions to array types, although there are conversions to references or pointers to arrays there is no conversion! so what is it on about? please help, just need to pass a bloody array of strings and set it to Menu class _choices[] attribute. thanks

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• How can I validate/secure/authenticate a JavaScript-based POST request?

  - by Bungle

  A product I'm helping to develop will basically work like this: A Web publisher creates a new page on their site that includes a <script> from our server. When a visitor reaches that new page, that <script> gathers the text content of the page and sends it to our server via a POST request (cross-domain, using a <form> inside of an <iframe>). Our server processes the text content and returns a response (via JSONP) that includes an HTML fragment listing links to related content around the Web. This response is cached and served to subsequent visitors until we receive another POST request with text content from the same URL, at which point we regenerate a "fresh" response. These POSTs only happen when our cached TTL expires, at which point the server signifies that and prompts the <script> on the page to gather and POST the text content again. The problem is that this system seems inherently insecure. In theory, anyone could spoof the HTTP POST request (including the referer header, so we couldn't just check for that) that sends a page's content to our server. This could include any text content, which we would then use to generate the related content links for that page. The primary difficulty in making this secure is that our JavaScript is publicly visible. We can't use any kind of private key or other cryptic identifier or pattern because that won't be secret. Ideally, we need a method that somehow verifies that a POST request corresponding to a particular Web page is authentic. We can't just scrape the Web page and compare the content with what's been POSTed, since the purpose of having JavaScript submit the content is that it may be behind a login system. Any ideas? I hope I've explained the problem well enough. Thanks in advance for any suggestions.

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• Should boost library be dependent on structure member alignments?

  - by Sorin Sbarnea

  I found, the hard way, that at least boost::program_options is dependent of the compiler configured structure member alignment. If you build boost using default settings and link it with a project using 4 bytes alignment (/Zp4) it will fail at runtime (made a minimal test with program_options). Boost will generate an assert indicating a possible bad calling convention but the real reason is the structure member alignment. Is there any way to prevent this? If the alignment makes the code incompatible shouldn't this be included in library naming?

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• Looping login with Facebook JS SDK and Rails

  - by nafe

  I'm using the Facebook JS SDK for single-sign with my rails app. I translated the php code from the Facebook example (at the bottom of the page under "Single Sign-on with the JavaScript SDK") into ruby. This appeared to be working great but I've noticed one user that gets continual redirects when trying to login. The logs look like: Processing UsersController#login (for X.X.X.X at 2010-05-22 17:25:55) [GET] Redirected to http://myapp.com/ Completed in 0ms (DB: 0) | 302 Found [http://myapp.com/login] (times as many entries as my unfortunate user leaves the browser redirecting in a loop). My client side code includes a callback with the "auth.sessionChange": FB.Event.subscribe('auth.sessionChange', function(response) { if (response.session) { // A user has logged in, and a new cookie has been saved window.location = "/login"; } else { // The user has logged out, and the cookie has been cleared window.location = "/logout"; } }); So it seems to me like this event is continually firing. Although, I can't test this theory because I can't recreate this scenario locally. I don't think it's the rails controller. The code here is just: def login # if first time user create db entry # now redirect back to where the user came from begin redirect_to :back rescue ActionController::RedirectBackError redirect_to root_url end end Does anyone have any idea on what's going on?

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