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• Some general C questions.

  - by b-gen-jack-o-neill

  Hello. I am trying to fully understand the process pro writing code in some language to execution by OS. In my case, the language would be C and the OS would be Windows. So far, I read many different articles, but I am not sure, whether I understand the process right, and I would like to ask you if you know some good articles on some subjects I couldn´t find. So, what I think I know about C (and basically other languages): C compiler itself handles only data types, basic math operations, pointers operations, and work with functions. By work with functions I mean how to pass argument to it, and how to get output from function. During compilation, function call is replaced by passing arguments to stack, and than if function is not inline, its call is replaced by some symbol for linker. Linker than find the function definition, and replace the symbol to jump adress to that function (and of course than jump back to program). If the above is generally true and I get it right, where to final .exe file actually linker saves the functions? After the main() function? And what creates the .exe header? Compiler or Linker? Now, additional capabilities of C, today known as C standart library is set of functions and the declarations of them, that other programmers wrote to extend and simplify use of C language. But these functions like printf() were (or could be?) written in different language, or assembler. And there comes my next question, can be, for example printf() function be written in pure C without use of assembler? I know this is quite big question, but I just mostly want to know, wheather I am right or not. And trust me, I read a lots of articles on the web, and I would not ask you, If I could find these infromation together on one place, in one article. Insted I must piece by piece gather informations, so I am not sure if I am right. Thanks.

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• How do I pass a callback function to sqlite3_exec on iOS 5.1?

  - by John Doh

  I am new to both xcode/iOS/Objective-C and sqlite. I am trying to teach myself the basics - and I would like to use the sqlite3 wrapper "sqlite3_exec" for a select query. For some reason, I can't find a simple example anywhere of someone doing this. Basically, the method has a parameter (the third one) for a callback function: int sqlite3_exec( sqlite3*, /* An open database */ const char *sql, /* SQL to be evaluated */ int (*callback)(void*,int,char**,char**), /* Callback function */ void *, /* 1st argument to callback */ char **errmsg /* Error msg written here */ ); That's fine. I'm no stranger to callbacks. However, I just can't seem to get the syntax down right. I took over one of the view controllers in my iPad (iOS 5.1) xcode (4.3) project, and made the changes shown below: #import "SecondViewController.h" #import "sqlite3.h" #import "AppState.h" @interface SecondViewController () @end @implementation SecondViewController - (int)myCallback:(void *)a_parm argc:(int)argc argv:(char **)argv column:(char **)column { return 0; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. //grab questionnaire names char *sql = "select * from QST2Main order by [Name]"; char *err = nil; sqlite3 *db = [[AppState sharedManager] getgCn]; sqlite3_exec(db, sql, myCallback, nil, &err); } Essentially, I want to run a query when this view first loads, to store some data for later use. But, XCode doesn't like the "myCallback" usage at the bottom there. It says: Undeclared Use of Identifier 'myCallback.' That method is declared in the header file, and I've even tried making it static. Nothing seems to make this error go away. I know I must be doing something fundamentally wrong here, but for the life of me I can't figure out what - I can't even find other code samples in this area that could help me figure out what I'm missing. Many thanks!

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• How to set focus to a brand new TextBox which was created as a result of a databinding in WPF?

  - by Mike

  Hi everyone, I have a WPF ItemsControl that is bound to an ObservableCollection. The XAML: <ItemsControl Name="mItemsControl"> <ItemsControl.ItemTemplate> <DataTemplate> <TextBox Text="{Binding Mode=OneWay}"></TextBox> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> The codebehind: private ObservableCollection<string> mCollection = new ObservableCollection<string>(); public MainWindow() { InitializeComponent(); this.mCollection.Add("Test1"); this.mCollection.Add("Test2"); this.mItemsControl.ItemsSource = this.mCollection; } private void Button_Click(object sender, RoutedEventArgs e) { this.mCollection.Add("new item!"); } When I click a button, it adds a new string to the databound ObservableCollection which triggers a new TextBox to appear. I want to give this new textbox focus. I've tried this technique from a related StackOverflow question but it always sets focus to the textbox before the newly created one. private void Button_Click(object sender, RoutedEventArgs e) { this.mCollection.Add("new item!"); // MoveFocus takes a TraversalRequest as its argument. TraversalRequest request = new TraversalRequest(FocusNavigationDirection.Previous); // Gets the element with keyboard focus. UIElement elementWithFocus = Keyboard.FocusedElement as UIElement; // Change keyboard focus. if (elementWithFocus != null) { elementWithFocus.MoveFocus(request); } } My need seems simple enough, but it's almost like the new textbox doesn't really exist until a slight delay after something is added to the ObservableCollection. Any ideas of what would work? Thanks! -Mike

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• sed/awk or other: one-liner to increment a number by 1 keeping spacing characters

  - by WizardOfOdds

  EDIT: I don't know in advance at which "column" my digits are going to be and I'd like to have a one-liner. Apparently sed doesn't do arithmetic, so maybe a one-liner solution based on awk? I've got a string: (notice the spacing) eh oh 37 and I want it to become: eh oh 36 (so I want to keep the spacing) Using awk I don't find how to do it, so far I have: echo "eh oh 37" | awk '$3>=0&&$3<=99 {$3--} {print}' But this gives: eh oh 36 (the spacing characters where lost, because the field separator is ' ') Is there a way to ask awk something like "print the output using the exact same field separators as the input had"? Then I tried yet something else, using awk's sub(..,..) method: ' sub(/[0-9][0-9]/, ...) {print}' but no cigar yet: I don't know how to reference the regexp and do arithmetic on it in the second argument (which I left with '...' for now). Then I tried with sed, but got stuck after this: echo "eh oh 37" | sed -e 's/\([0-9][0-9]\)/.../' Can I do arithmetic from sed using a reference to the matching digits and have the output not modify the number of spacing characters? Note that it's related to my question concerning Emacs and how to apply this to some (big) Emacs region (using a replace region with Emacs's shell-command-on-region) but it's not an identical question: this one is specifically about how to "keep spaces" when working with awk/sed/etc.

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• AES Encryption Java Invalid Key length

  - by wuntee

  I am trying to create an AES encryption method, but for some reason I keep getting a 'java.security.InvalidKeyException: Key length not 128/192/256 bits'. Here is the code: public static SecretKey getSecretKey(char[] password, byte[] salt) throws NoSuchAlgorithmException, InvalidKeySpecException{ SecretKeyFactory factory = SecretKeyFactory.getInstance("PBEWithMD5AndDES"); // NOTE: last argument is the key length, and it is 256 KeySpec spec = new PBEKeySpec(password, salt, 1024, 256); SecretKey tmp = factory.generateSecret(spec); SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES"); return(secret); } public static byte[] encrypt(char[] password, byte[] salt, String text) throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, InvalidParameterSpecException, IllegalBlockSizeException, BadPaddingException, UnsupportedEncodingException{ SecretKey secret = getSecretKey(password, salt); Cipher cipher = Cipher.getInstance("AES"); // NOTE: This is where the Exception is being thrown cipher.init(Cipher.ENCRYPT_MODE, secret); byte[] ciphertext = cipher.doFinal(text.getBytes("UTF-8")); return(ciphertext); } Can anyone see what I am doing wrong? I am thinking it may have something to do with the SecretKeyFactory algorithm, but that is the only one I can find that is supported on the end system I am developing against. Any help would be appreciated. Thanks.

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• Makefile for DOS/Windows and Cygwin

  - by Thomas Matthews

  I need to have a makefile work under DOS (Windows) and Cygwin. I having problems with the makefile detecting the OS correctly and setting appropriate variables. The objective is to set variables for the following commands, then invoke the commands in rules using the variables: Delete file: rm in Cygwin, del in DOS. Remove directory: rmdir (different parameters in Cygwin and DOS) Copy file: cp in Cygwin, copy in DOS. Testing for file existance: test in Cygwin, IF EXIST in DOS. Listing contents of a file: cat in Cygwin, type in DOS. Here is my attempt, which always uses the else clause: OS_KIND = $(OSTYPE) #OSTYPE is an environment variable set by Cygwin. ifeq ($(OS_KIND), cygwin) ENV_OS = Cygwin RM = rm -f RMDIR = rmdir -r CP = cp REN = mv IF_EXIST = test -a IF_NOT_EXIST = ! test -a LIST_FILE = cat else ENV_OS = Win_Cmd RM = del -f -Q RMDIR = rmdir /S /Q IF_EXIST = if exist IF_NOT_EXIST = if not exist LIST_FILE = type endif I'm using the forward slash character, '/', as a directory separator. This is a problem with the DOS command, as it is interpreting it as program argument rather than a separator. Anybody know how to resolve this issue? Edit: I am using make with Mingw in both Windows Console (DOS) and Cygwin.

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• TableView Cells unresponsive

  - by John Donovan

  I have a TableView and I wish to be able to press several cells one after the other and have messages appear. At the moment the cells are often unresponsive. I found some coed for a similar problem someone was kind enough to post, however, although he claimed it worked 100% it doesn't work for me. The app won't even build. Here's the code: -(UIView*) hitTest:(CGPoint)point withEvent:(UIEvent*)event { // check to see if the hit is in this table view if ([self pointInside:point withEvent:event]) { UITableViewCell* newCell = nil; // hit is in this table view, find out // which cell it is in (if any) for (UITableViewCell* aCell in self.visibleCells) { if ([aCell pointInside:[self convertPoint:point toView:aCell] withEvent:nil]) { newCell = aCell; break; } } // if it touched a different cell, tell the previous cell to resign // this gives it a chance to hide the keyboard or date picker or whatever if (newCell != activeCell) { [activeCell resignFirstResponder]; self.activeCell = newCell; // may be nil } } // return the super's hitTest result return [super hitTest:point withEvent:event]; } With this code I get this warning: that my viewController may not respond to pointsInside:withEvent (it's a TableViewController). I also get some faults: request for member 'visibleCells' in something not a structure or a union. incompatible type for argument 1 of pointInsideWithEvent, expression does not have a valid object type and similar. I must admit I'm not so good at reading other people's code but I was wondering whether the problems here are obvious and if so if anyone could give me a pointer it would be greatly appreciated.

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• Error when trying to connect to Jacorb naming service

  - by Dopyiii

  I'm hoping to get some help with this weird problem. We're running the Jacorb name server and I have a simple client that I'm using to try to connect and do awesome CORBA voodoo. The name server is running, but when I try to start my java app, I get a "Connection failure" error (org.omg.CORBA.COMM_FAILURE, minor code 201, "caused by java.net.ConnectionException: Connection refused: connect"). Here's the weird part. The error reports that it's trying to connect using the default port 900, but I'm passing in an argument to try to override the port number of the name service to match the one being used by the name server. My java command is like this: java -classpath . HelloClient -Djava.endorsed.dirs="bla bla bla" -Dorg.omg.CORBA.ORBClass=org.jacorb.orb.ORB -Dorg.omg.CORBA.ORBSingletonClass=org.jacorb.orb.ORBSingleton -DORBInitRef.NameService=corbaloc::localhost:2809/StandardNS/NameServer-POA/_root I also tried the parameters without the first capital D (I've seen it both ways and I don't know the difference). Now, if I put in -ORBInitialPort 2809, then the client does appear to try to connect, but then I get a corba.OBJECT_NOT_EXIST error. I could use any help or advise anyone has.

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• Why does Java's invokevirtual need to resolve the called method's compile-time class?

  - by Chris

  Consider this simple Java class: class MyClass { public void bar(MyClass c) { c.foo(); } } I want to discuss what happens on the line c.foo(). At the bytecode level, the meat of c.foo() will be the invokevirtual opcode, and, according to the documentation for invokevirtual, more or less the following will happen: Look up the foo method defined in compile-time class MyClass. (This involves first resolving MyClass.) Do some checks, including: Verify that c is not an initialization method, and verify that calling MyClass.foo wouldn't violate any protected modifiers. Figure out which method to actually call. In particular, look up c's runtime type. If that type has foo(), call that method and return. If not, look up c's runtime type's superclass; if that type has foo, call that method and return. If not, look up c's runtime type's superclass's superclass; if that type has foo, call that method and return. Etc.. If no suitable method can be found, then error. Step #3 alone seems adequate for figuring out which method to call and verifying that said method has the correct argument/return types. So my question is why step #1 gets performed in the first place. Possible answers seem to be: You don't have enough information to perform step #3 until step #1 is complete. (This seems implausible at first glance, so please explain.) The linking or access modifier checks done in #1 and #2 are essential to prevent certain bad things from happening, and those checks must be performed based on the compile-time type, rather than the run-time type hierarchy. (Please explain.)

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• boost::binding that which is already bound

  - by PaulH

  I have a Visual Studio 2008 C++ application that does something like this: template< typename Fcn > inline void Bar( Fcn fcn ) // line 84 { fcn(); }; template< typename Fcn > inline void Foo( Fcn fcn ) { // this works fine Bar( fcn ); // this fails to compile boost::bind( Bar, fcn )(); }; void main() { SYSTEM_POWER_STATUS_EX status = { 0 }; Foo( boost::bind( ::GetSystemPowerStatusEx, &status, true ) ); // line 160 } *The call to GetSystemPowerStatusEx() is just for demonstration. Insert your favorite call there and the behavior is the same. When I go to compile this, I get 84 errors. I won't post them all unless asked, but they start with this: 1>.\MyApp.cpp(99) : error C2896: 'boost::_bi::bind_t<_bi::dm_result<MT::* ,A1>::type,boost::_mfi::dm<M,T>,_bi::list_av_1<A1>::type> boost::bind(M T::* ,A1)' : cannot use function template 'void Bar(Fcn)' as a function argument 1> .\MyApp.cpp(84) : see declaration of 'Bar' 1> .\MyApp.cpp(160) : see reference to function template instantiation 'void Foo<boost::_bi::bind_t<R,F,L>>(Fcn)' being compiled 1> with 1> [ 1> R=BOOL, 1> F=BOOL (__cdecl *)(PSYSTEM_POWER_STATUS_EX,BOOL), 1> L=boost::_bi::list2<boost::_bi::value<_SYSTEM_POWER_STATUS_EX *>,boost::_bi::value<bool>>, 1> Fcn=boost::_bi::bind_t<BOOL,BOOL (__cdecl *)(PSYSTEM_POWER_STATUS_EX,BOOL),boost::_bi::list2<boost::_bi::value<_SYSTEM_POWER_STATUS_EX *>,boost::_bi::value<bool>>> 1> ] If anybody can point out what I may be doing wrong, I would appreciate it. Thanks, PaulH

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• Why user control with code behind file doesn't want to compile under MVC2?

  - by kyrisu

  I have user control in my MVC2 app placed in the Content folder (it's not supposed to be a view, just reusable part of the app). UserControl1.ascx looks like: <@ Control AutoEventWireup="true" Language="C#" CodeFile="~/Content/UserControl1.ascx.cs" Inherits="MVCDrill.Content.UserControl1" %> <div runat="server" id="mydiv"> <asp:LinkButton id="lb_text" runat="server"></asp:LinkButton> </div> UserControl1.ascx.cs looks like: using System; using System.Web; using System.Web.UI; namespace MVCDrill.Content { public class UserControl1 : UserControl { public string Text { get { return this.lb_text.Text; } set { this.lb_text.Text = value; } } } } I'm pretty sure this kind of stuff compiled under webforms but I'm getting compilation error: 'MVCDrill.Content.UserControl1' does not contain a definition for 'lb_text' and no extension method 'lb_text' accepting a first argument of type 'MVCDrill.Content.UserControl1' could be found (are you missing a using directive or an assembly reference?) Am I missing something? How to change it (what is the alternative) in MVC2 ? p.s. Intellisense sees lb_text with no problem. I've tried with different controls with the same outcome.

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• PHP cURL JSON Decode (X-AUTH Header)

  - by TheCyX

  <?php // Show Profile $curl = curl_init(); curl_setopt ($curl, CURLOPT_URL, "https://example/api"); curl_setopt ($curl, CURLOPT_RETURNTRANSFER, true); curl_setopt ($curl, CURLOPT_HTTPAUTH, CURLAUTH_BASIC ) ; curl_setopt ($curl, CURLOPT_HTTPHEADER, array('X-AUTH: 123456789')); $projects = curl_exec($curl); // This is empty? echo $projects; //Decode $phpArray = json_decode($projects); print_r($phpArray); foreach ($phpArray as $key => $value) { // Line 17, sure its empty, but why? echo "<p>$key | $value</p>"; } ?> Warning: Invalid argument supplied for foreach() in /html/api.php on line 17 The API needs this authentification: $ curl -i -H "X-AUTH: 123456789" https://example/api JSON File: {"id":"123456","hostId":null,"Nickname":"thecyx","DisplayName":"thecyx","AppDisplayName":"thecyx","Score":"300","Account":"Full"} The $project variable is empty. If I'm posting the API Url in the Broswer its working. And, if possible, what's the correct way to get the JSON Data e.g. [Nickname],[Score]?

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• Can't operator == be applied to generic types in C#?

  - by Hosam Aly

  According to the documentation of the == operator in MSDN, For predefined value types, the equality operator (==) returns true if the values of its operands are equal, false otherwise. For reference types other than string, == returns true if its two operands refer to the same object. For the string type, == compares the values of the strings. User-defined value types can overload the == operator (see operator). So can user-defined reference types, although by default == behaves as described above for both predefined and user-defined reference types. So why does this code snippet fail to compile? void Compare<T>(T x, T y) { return x == y; } I get the error Operator '==' cannot be applied to operands of type 'T' and 'T'. I wonder why, since as far as I understand the == operator is predefined for all types? Edit: Thanks everybody. I didn't notice at first that the statement was about reference types only. I also thought that bit-by-bit comparison is provided for all value types, which I now know is not correct. But, in case I'm using a reference type, would the the == operator use the predefined reference comparison, or would it use the overloaded version of the operator if a type defined one? Edit 2: Through trial and error, we learned that the == operator will use the predefined reference comparison when using an unrestricted generic type. Actually, the compiler will use the best method it can find for the restricted type argument, but will look no further. For example, the code below will always print true, even when Test.test<B>(new B(), new B()) is called: class A { public static bool operator==(A x, A y) { return true; } } class B : A { public static bool operator==(B x, B y) { return false; } } class Test { void test<T>(T a, T b) where T : A { Console.WriteLine(a == b); } }

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• MVC View Model Intellisense / Compile error

  - by Marty Trenouth

  I have one Library with my ORM and am working with a MVC Application. I have a problem where the pages won't compile because the Views can't see the Model's properties (which are inherited from lower level base classes). They system throws a compile error saying that 'object' does not contain a definition for 'ID' and no extension method 'ID' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?) implying that the View is not seeing the model. In the Controller I have full access to the Model and have check the Inherits from portion of the view to validate the correct type is being passed. Controller: return View(new TeraViral_Blog()); View: <%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<com.models.TeraViral_Blog>" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server"> Index2 </asp:Content> <asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server"> <h2>Index2</h2> <fieldset> <legend>Fields</legend> <p> ID: <%= Html.Encode(Model.ID) %> </p> </fieldset> </asp:Content>

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• Instantiating class with custom allocator in shared memory

  - by recipriversexclusion

  I'm pulling my hair due to the following problem: I am following the example given in boost.interprocess documentation to instantiate a fixed-size ring buffer buffer class that I wrote in shared memory. The skeleton constructor for my class is: template<typename ItemType, class Allocator > SharedMemoryBuffer<ItemType, Allocator>::SharedMemoryBuffer( unsigned long capacity ){ m_capacity = capacity; // Create the buffer nodes. m_start_ptr = this->allocator->allocate(); // allocate first buffer node BufferNode* ptr = m_start_ptr; for( int i = 0 ; i < this->capacity()-1; i++ ) { BufferNode* p = this->allocator->allocate(); // allocate a buffer node } } My first question: Does this sort of allocation guarantee that the buffer nodes are allocated in contiguous memory locations, i.e. when I try to access the n'th node from address m_start_ptr + n*sizeof(BufferNode) in my Read() method would it work? If not, what's a better way to keep the nodes, creating a linked list? My test harness is the following: // Define an STL compatible allocator of ints that allocates from the managed_shared_memory. // This allocator will allow placing containers in the segment typedef allocator<int, managed_shared_memory::segment_manager> ShmemAllocator; //Alias a vector that uses the previous STL-like allocator so that allocates //its values from the segment typedef SharedMemoryBuffer<int, ShmemAllocator> MyBuf; int main(int argc, char *argv[]) { shared_memory_object::remove("MySharedMemory"); //Create a new segment with given name and size managed_shared_memory segment(create_only, "MySharedMemory", 65536); //Initialize shared memory STL-compatible allocator const ShmemAllocator alloc_inst (segment.get_segment_manager()); //Construct a buffer named "MyBuffer" in shared memory with argument alloc_inst MyBuf *pBuf = segment.construct<MyBuf>("MyBuffer")(100, alloc_inst); } This gives me all kinds of compilation errors related to templates for the last statement. What am I doing wrong?

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• Reference-type conversion operators: asking for trouble?

  - by Ben

  When I compile the following code using g++ class A {}; void foo(A&) {} int main() { foo(A()); return 0; } I get the following error messages: > g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:10: error: invalid initialization of non-const reference of type ‘A&’ from a temporary of type ‘A’ test.cpp:6: error: in passing argument 1 of ‘void foo(A&)’ After some reflection, these errors make plenty of sense to me. A() is just a temporary value, not an assignable location on the stack, so it wouldn't seem to have an address. If it doesn't have an address, then I can't hold a reference to it. Okay, fine. But wait! If I add the following conversion operator to the class A class A { public: operator A&() { return *this; } }; then all is well! My question is whether this even remotely safe. What exactly does this point to when A() is constructed as a temporary value? I am given some confidence by the fact that void foo(const A&) {} can accept temporary values according to g++ and all other compilers I've used. The const keyword can always be cast away, so it would surprise me if there were any actual semantic differences between a const A& parameter and an A& parameter. So I guess that's another way of asking my question: why is a const reference to a temporary value considered safe by the compiler whereas a non-const reference is not?

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• Dilemma of Sending a Byte Array from JavaScript to COM.

  - by Voulnet

  Hello there, I'm having a bit of a problem because neither Javascript nor ActiveX (written in C++) are behaving like good little children. All I'm asking them to do is for Javascript to send a byte array and for the ActiveX to receive the byte array correctly in order to do more computation. This is how I declared my byte array in JS, and I verified it inside JS: var arr = new Array(0x00, 0xA4, 0x04, 0x00, 0x10,0xA0, 0x00, 00, 00, 0x18, 0x30, 0x03, 0x01, 00, 00, 00, 00, 00, 00, 00, 00); Javascript sends this array as an argument to an ActiveX method. Here is the tricky part; I want the ActiveX method to receive the byte array as a SAFEARRAY or VARIANT, but I can't get it to work for the life of me. I tried debugging and seeing the contents received inside the ActiveX as both SAFEARRAY or VARIANT, but to no avail. Here is the IDL segment: [id(7), helpstring("NEW Sends APDU to Card and Reads the Response")] HRESULT NewSendAPDU( [in] VARIANT pAPDU, [out, retval]VARIANT* pAPDUResponse); Any help is greatly appreciated. Thanks in advance!

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• Autodetect Presence of CSV Headers in a File

  - by banzaimonkey

  Short question: How do I automatically detect whether a CSV file has headers in the first row? Details: I've written a small CSV parsing engine that places the data into an object that I can access as (approximately) an in-memory database. The original code was written to parse third-party CSV with a predictable format, but I'd like to be able to use this code more generally. I'm trying to figure out a reliable way to automatically detect the presence of CSV headers, so the script can decide whether to use the first row of the CSV file as keys / column names or start parsing data immediately. Since all I need is a boolean test, I could easily specify an argument after inspecting the CSV file myself, but I'd rather not have to (go go automation). I imagine I'd have to parse the first 3 to ? rows of the CSV file and look for a pattern of some sort to compare against the headers. I'm having nightmares of three particularly bad cases in which: The headers include numeric data for some reason The first few rows (or large portions of the CSV) are null There headers and data look too similar to tell them apart If I can get a "best guess" and have the parser fail with an error or spit out a warning if it can't decide, that's OK. If this is something that's going to be tremendously expensive in terms of time or computation (and take more time than it's supposed to save me) I'll happily scrap the idea and go back to working on "important things". I'm working with PHP, but this strikes me as more of an algorithmic / computational question than something that's implementation-specific. If there's a simple algorithm I can use, great. If you can point me to some relevant theory / discussion, that'd be great, too. If there's a giant library that does natural language processing or 300 different kinds of parsing, I'm not interested.

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• bash - how to filter java exception info

  - by Michael Mao

  Hi all: We've got a multi-agent Java environment where different agent would most likely produce all sorts of exceptions thrown to stderr. Here is a sample taken from the huge exception log **java.security.AccessControlException: access denied (java.io.FilePermission ..\tournament\Driver\HotelRoomAnalyser.class read)** at java.security.AccessControlContext.checkPermission(Unknown Source) at java.security.AccessController.checkPermission(Unknown Source) at java.lang.SecurityManager.checkPermission(Unknown Source) at java.lang.SecurityManager.checkRead(Unknown Source) at java.io.File.length(Unknown Source) at emarket.client.EmarketSandbox$SandboxFileLoader.loadClassData(EmarketSandbox.java:218) at emarket.client.EmarketSandbox$SandboxFileLoader.loadClass(EmarketSandbox.java:199) at java.lang.ClassLoader.loadClass(Unknown Source) **java.security.AccessControlException: access denied (java.io.FilePermission ..\tournament\Driver\HotelRoomAnalyser.class read)** at java.security.AccessControlContext.checkPermission(Unknown Source) at java.security.AccessController.checkPermission(Unknown Source) at java.lang.SecurityManager.checkPermission(Unknown Source) at java.lang.SecurityManager.checkRead(Unknown Source) at java.io.File.length(Unknown Source) at emarket.client.EmarketSandbox$SandboxFileLoader.loadClassData(EmarketSandbox.java:218) at emarket.client.EmarketSandbox$SandboxFileLoader.loadClass(EmarketSandbox.java:199) at java.lang.ClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClassInternal(Unknown Source) at MySmarterAgent.hotelRoomBookings(MySmarterAgent.java:108) fortunately all top-tier exceptions are denoted by no leading spaces, as wrapped by ** above. My concern is to get all of the top-tier exception name (delimited by colon :), together with the first line below which contains something like at emarket.client.EmarketSandbox$SandboxFileLoader.loadClassData(EmarketSandbox.java:218) Basically, something with padded style, starts with "at" and ends with ".java:108" So this info can be forwarded to the owner of that error-prone agent and let him/her fix it. My code in ~/.bashrc is incompleted now : alias startmatch='java -jar "emarket.jar" ../tournament 100'; function geterrors() { startmatch 2>"$1"; a=0; while read line do if true; then a=$(($a+1)); echo $a; fi; done } What it does now is to redirect all stderr to a text file specified by the first argument passed in, and after that, parse that text file line by line, if certain conditions returns true, echo only that line. And I am stuck with what to do inside the loop. Any suggestion is much appreciates, any hint is welcomed.

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• BitmapFrame in another thread

  - by Lasse Lindström

  Hi I am using a WPF BackgroundWorker to create thumbnails. My worker function looks like: private void work(object sender, DoWorkEventArgs e) { try { var paths = e.Argument as string[]; var boxList = new List(); foreach (string path in paths) { if (!string.IsNullOrEmpty(path)) { FileInfo info = new FileInfo(path); if (info.Exists && info.Length 0) { BitmapImage bi = new BitmapImage(); bi.BeginInit(); bi.DecodePixelWidth = 200; bi.CacheOption = BitmapCacheOption.OnLoad; bi.UriSource = new Uri(info.FullName); bi.EndInit(); var item = new BoxItem(); item.FilePath = path; MemoryStream ms = new MemoryStream(); PngBitmapEncoder encoder = new PngBitmapEncoder(); encoder.Frames.Add(BitmapFrame.Create(bi)); encoder.Save(ms); item.ThumbNail = ms.ToArray(); ms.Close(); boxList.Add(item); } } } e.Result = boxList; } catch (Exception ex) { //nerver comes here } } When this fuction is finnished and before the BackgroundWorker "Completed" function is started, I can see on the output window on Vs2008, that a exception is generated. It looks like: A first chance exception of type 'System.NotSupportedException' occurred in PresentationCore.dll The number of exceptions generates equals the number of thumbnails to be generated. Using "trial and error" I have isolated the problem to: BitmapFrame.Create(bi) Removing that line (makes my function useless) also removes the exception. I have not found any explanation to this,,, or a better method to create thumbnails i a background thread. Can anyone help me? //lasse

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• Are CMake GLOB and source_group compatible?

  - by jwfearn

  I'm using CMake 2.8.0 (on Windows) with the "Visual Studio 10 Win64" generator. GLOB and source_group don't seem to work together. Is there a way to get this to work? I use file( GLOB ... ) to create a list of .cpp files and then use source_group to create a filter in the generated Visual Studio project: # C:\Users\My Name\hello\CMakeLists.txt cmake_minimum_required( VERSION 2.8 ) project( hello_proj ) file( GLOB HELLO_SRCS *.cpp ) message( "HELLO_SRCS="${HELLO_SRCS} ) #source_group( hello_group ${HELLO_SRCS} ) #line 6: uncomment to get error add_executable( hello_exec ${HELLO_SRCS} ) with line 6 commented out, the project is generated fine: HELLO_SRCS=C:/Users/My Name/hello/hello.cppC:/Users/My Name/hello/print_line.cpp -- Configuring done -- Generating done -- Build files have been written to: C:/Users/My Name/hello with line 6 un-commented, I get an error: HELLO_SRCS=C:/Users/My Name/hello/hello.cppC:/Users/My Name/hello/print_line.cpp CMake Error at CMakeLists.txt:6 (source_group): source_group Unknown argument "C:/Users/My Name/hello/hello.cpp". Perhaps the FILES keyword is missing. -- Configuring incomplete, errors occurred! I notice that output value of ${HELLO_SRCS} does not seem to contain any delimiters between the file names, nor does it have quotes or other delimiters wrapping the file names which contain spaces. Does that have anything to do with my problem? Renaming all directories to avoid spaces is not really an option.

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• Why do the overloads of String.Format exist?

  - by GiddyUpHorsey

  I was using Reflector to look at the implementation of String.Format and had always been under the impression that the overloads of String.Format that took 1, 2 & 3 arguments were optimized versions of the method that takes an object array. However, what I found was that internally they create an object array and then call a method that takes an object array. 1 arg public static string Format(string format, object arg0) { if (format == null) { throw new ArgumentNullException("format"); } return Format(null, format, new object[] { arg0 }); } 2 args public static string Format(string format, object arg0, object arg1) { if (format == null) { throw new ArgumentNullException("format"); } return Format(null, format, new object[] { arg0, arg1 }); } 3 args public static string Format(string format, object arg0, object arg1, object arg2) { if (format == null) { throw new ArgumentNullException("format"); } return Format(null, format, new object[] { arg0, arg1, arg2 }); } Object array public static string Format(string format, params object[] args) { if ((format == null) || (args == null)) { throw new ArgumentNullException((format == null) ? "format" : "args"); } return Format(null, format, args); } Internally they all end up using the same code and so using the 1, 2 & 3 argument versions are no faster than the object array version. So my question is - why do they exist? When you use the object array version with a comma separated list of values, the compiler automatically converts the arguments into an object array because of the params/ParamArray keyword which is essentially what the 1, 2 & 3 versions do, so they seem redundant. Why did the BCL designers add these overloads?

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• Java design: too many getters

  - by dege

  After writing a few lesser programs when learning Java the way I've designed the programs is with Model-View-Control. With using MVC I have a plethora of getter methods in the model for the view to use. It feels that while I gain on using MVC, for every new value added I have to add two new methods in the model which quickly get all cluttered with getter & setters. So I was thinking, maybe I should use the notifyObserver method that takes an argument. But wouldn't feel very smart to send every value by itself either so I figured, maybe if I send a kind of container with all the values, preferably only those that actually changed. What this would accomplish would be that instead of having a whole lot of getter methods I could just have one method in the model which put all relevant values in the container. Then in the view I would have a method called from the update which extracted the values from the container and assigning them to the correct fields. I have two questions concerning this. First: is this actually a viable way to do this. Would you recommend me doing something along these lines? Secondly: if I do use this plan and I don't want to keep sending fields that didn't actually change. How would I handle that without having to have if statements to check if the value is not null for every single value?

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• Please explain JSONP

  - by Cheeso

  I don't understand jsonp. I understand JSON. I don't understand JSONP. Wikipedia is the top search result for JSONP. It says JSONP or "JSON with padding" is a JSON extension wherein a prefix is specified as an input argument of the call itself. Huh? What call? That doesn't make any sense to me. JSON is a data format. There's no call. The 2nd search result is from some guy named Remy, who writes JSONP is script tag injection, passing the response from the server in to a user specified function. I can sort of understand that, but it's still not making any sense. What is JSONP, why was it created (what problem does it solve), and why would I use it? Addendum: I've updated Wikipedia with a clearer and more thorough description of JSONP, based on jvenema's answer. Thanks, all.

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• What are the most interesting equivalences arising from the Curry-Howard Isomorphism?

  - by Tom

  I came upon the Curry-Howard Isomorphism relatively late in my programming life, and perhaps this contributes to my being utterly fascinated by it. It implies that for every programming concept there exists a precise analogue in formal logic, and vice versa. Here's an "obvious" list of such analogies, off the top of my head: program/definition | proof type/declaration | proposition inhabited type | theorem function | implication function argument | hypothesis/antecedent function result | conclusion/consequent function application | modus ponens recursion | induction identity function | tautology non-terminating function | absurdity tuple | conjunction (and) disjoint union | exclusive disjunction (xor) parametric polymorphism | universal quantification So, to my question: what are some of the more interesting/obscure implications of this isomorphism? I'm no logician so I'm sure I've only scratched the surface with this list. For example, here are some programming notions for which I'm unaware of pithy names in logic: currying | "((a & b) => c) iff (a => (b => c))" scope | "known theory + hypotheses" And here are some logical concepts which I haven't quite pinned down in programming terms: primitive type? | axiom set of valid programs? | theory ? | disjunction (or)

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