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• Generate static gallery

  - by theomega

  Hy, I need a (linux/shell) script which does the following: It takes a folder full of jpg-files, generates thumbnails and previews (maybe using imagemagik's convert) and creates a html-page which includes all the thumbnails, opens a preview using something like LightBox and links to the original size. Does somebody know a script which does this? I could write one on my own, but it would save me some time.

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• What's the relationship between meta-circular interpreters, virtual machines and increased performance?

  - by Gomi

  I've read about meta-circular interpreters on the web (including SICP) and I've looked into the code of some implementations (such as PyPy and Narcissus). I've read quite a bit about two languages which made great use of metacircular evaluation, Lisp and Smalltalk. As far as I understood Lisp was the first self-hosting compiler and Smalltalk had the first "true" JIT implementation. One thing I've not fully understood is how can those interpreters/compilers achieve so good performance or, in other words, why is PyPy faster than CPython? Is it because of reflection? And also, my Smalltalk research led me to believe that there's a relationship between JIT, virtual machines and reflection. Virtual Machines such as the JVM and CLR allow a great deal of type introspection and I believe they make great use it in Just-in-Time (and AOT, I suppose?) compilation. But as far as I know, Virtual Machines are kind of like CPUs, in that they have a basic instruction set. Are Virtual Machines efficient because they include type and reference information, which would allow language-agnostic reflection? I ask this because many both interpreted and compiled languages are now using bytecode as a target (LLVM, Parrot, YARV, CPython) and traditional VMs like JVM and CLR have gained incredible boosts in performance. I've been told that it's about JIT, but as far as I know JIT is nothing new since Smalltalk and Sun's own Self have been doing it before Java. I don't remember VMs performing particularly well in the past, there weren't many non-academic ones outside of JVM and .NET and their performance was definitely not as good as it is now (I wish I could source this claim but I speak from personal experience). Then all of a sudden, in the late 2000s something changed and a lot of VMs started to pop up even for established languages, and with very good performance. Was something discovered about the JIT implementation that allowed pretty much every modern VM to skyrocket in performance? A paper or a book maybe?

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• What is the general feeling about reflection extensions in std::type_info?

  - by Evan Teran

  I've noticed that reflection is one feature that developers from other languages find very lacking in c++. For certain applications I can really see why! It is so much easier to write things like an IDE's auto-complete if you had reflection. And certainly serialization APIs would be a world easier if we had it. On the other side, one of the main tenets of c++ is don't pay for what you don't use. Which makes complete sense. That's something I love about c++. But it occurred to me there could be a compromise. Why don't compilers add extensions to the std::type_info structure? There would be no runtime overhead. The binary could end up being larger, but this could be a simple compiler switch to enable/disable and to be honest, if you are really concerned about the space savings, you'll likely disable exceptions and RTTI anyway. Some people cite issues with templates, but the compiler happily generates std::type_info structures for template types already. I can imagine a g++ switch like -fenable-typeinfo-reflection which could become very popular (and mainstream libs like boost/Qt/etc could easily have a check to generate code which uses it if there, in which case the end user would benefit with no more cost than flipping a switch). I don't find this unreasonable since large portable libraries like this already depend on compiler extensions. So why isn't this more common? I imagine that I'm missing something, what are the technical issues with this?

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• VB .Net - Reflection: Reflected Method from a loaded Assembly executes before calling method. Why?

  - by pu.griffin

  When I am loading an Assembly dynamically, then calling a method from it, I appear to be getting the method from Assembly executing before the code in the method that is calling it. It does not appear to be executing in a Serial manner as I would expect. Can anyone shine some light on why this might be happening. Below is some code to illustrate what I am seeing, the code from the some.dll assembly calls a method named PerformLookup. For testing I put a similar MessageBox type output with "PerformLookup Time: " as the text. What I end up seeing is: First: "PerformLookup Time: 40:842" Second: "initIndex Time: 45:873" Imports System Imports System.Data Imports System.IO Imports Microsoft.VisualBasic.Strings Imports System.Reflection Public Class Class1 Public Function initIndex(indexTable as System.Collections.Hashtable) As System.Data.DataSet Dim writeCode As String MessageBox.Show("initIndex Time: " & Date.Now.Second.ToString() & ":" & Date.Now.Millisecond.ToString()) System.Threading.Thread.Sleep(5000) writeCode = RefreshList() End Function Public Function RefreshList() As String Dim asm As System.Reflection.Assembly Dim t As Type() Dim ty As Type Dim m As MethodInfo() Dim mm As MethodInfo Dim retString as String retString = "" Try asm = System.Reflection.Assembly.LoadFrom("C:\Program Files\some.dll") t = asm.GetTypes() ty = asm.GetType(t(28).FullName) 'known class location m = ty.GetMethods() mm = ty.GetMethod("PerformLookup") Dim o as Object o = Activator.CreateInstance(ty) Dim oo as Object() retString = mm.Invoke(o,Nothing).ToString() Catch Ex As Exception End Try return retString End Function End Class

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• Why are static classes considered “classes” and “reference types”?

  - by Timwi

  I’ve been pondering about the C# and CIL type system today and I’ve started to wonder why static classes are considered classes. There are many ways in which they are not really classes: A “normal” class can contain non-static members, a static class can’t. In this respect, a class is more similar to a struct than it is to a static class, and yet structs have a separate name. You can have a reference to an instance of a “normal” class, but not a static class (despite it being considered a “reference type”). In this respect, a class is more similar to an interface than it is to a static class, and yet interfaces have a separate name. The name of a static class can never be used in any place where a type name would normally fit: you can’t declare a variable of this type, you can’t use it as a base type, and you can’t use it as a generic type parameter. In this respect, static classes are somewhat more like namespaces. A “normal” class can implement interfaces. Once again, that makes classes more similar to structs than to static classes. A “normal” class can inherit from another class. It is also bizarre that static classes are considered to derive from System.Object. Although this allows them to “inherit” the static methods Equals and ReferenceEquals, the purpose of that inheritance is questionable as you would call those methods on object anyway. C# even allows you to specify that useless inheritance explicitly on static classes, but not on interfaces or structs, where the implicit derivation from object and System.ValueType, respectively, actually has a purpose. Regarding the subset-of-features argument: Static classes have a subset of the features of classes, but they also have a subset of the features of structs. All of the things that make a class distinct from the other kinds of type, do not seem to apply to static classes. Regarding the typeof argument: Making a static class into a new and different kind of type does not preclude it from being used in typeof. Given the sheer oddity of static classes, and the scarcity of similarities between them and “normal” classes, shouldn’t they have been made into a separate kind of type instead of a special kind of class?

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• Variables in static library are never initialized. Why?

  - by Coyote

  I have a bunch of variables that should be initialized then my game launches, but must of them are never initialized. Here is an example of the code: MyClass.h class MyClass : public BaseObject { DECLARE_CLASS_RTTI(MyClass, BaseObject); ... }; MyClass.cpp REGISTER_CLASS(MyClass) Where REGISTER_CLASS is a macro defined as follow #define REGISTER_CLASS(className)\ class __registryItem##className : public __registryItemBase {\ virtual className* Alloc(){ return NEW className(); }\ virtual BaseObject::RTTI& GetRTTI(){ return className::RTTI; }\ }\ \ const __registryItem##className __registeredItem##className(#className); and __registryItemBase looks like this: class __registryItemBase { __registryItemBase(const _string name):mName(name){ ClassRegistry::Register(this); } const _string mName; virtual BaseObject* Alloc() = 0; virtual BaseObject::RTTI& GetRTTI() = 0; } Now the code is similar to what I currently have and what I have works flawlessly, all the registered classes are registered to a ClassManager before main(...) is called. I'm able to instantiate and configure components from scripts and auto-register them to the right system etc... The problem arrises when I create a static library (currently for the iPhone, but I fear it will happen with android as well). In that case the code in the .cpp files is never registered. Why is the resulting code not executed when it is in the library while the same code in the program's binary is always executed? Bonus questions: For this to work in the static library, what should I do? Is there something I am missing? Do I need to pass a flag when building the lib? Should I create another structure and init all the __registeredItem##className using that structure?

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• Static method not called

  - by Smile

  I'm trying to call a static method (printABC()) in this class but it's not working. If I uncomment both of the lines marked T_T (1 and 2), it works! Why does it fail with only one of the lines? import java.util.Scanner; class pro0009 { static Scanner in = new Scanner(System.in); static int A,B,C; static void printABC(){ String ABC = in.nextLine(); ABC=ABC.replace("A"," "+A+" "); ABC=ABC.replace("B"," "+B+" "); ABC=ABC.replace("C"," "+C+" "); //System.out.print(ABC.substring(1)); System.out.print(ABC); } public static void main(String[] args){ int x = in.nextInt(); //1 int y = in.nextInt(); //2 int z = in.nextInt(); //3 if(x<y){//1<2 if(x<z){ //1<3 if(y<z){//x<y<z 2<3 //1<2<3 A=x; B=y; C=z; printABC();//T_T 1 System.out.println("Here"); //pro0009.printABC();//T_T 2 //System.out.println("Here2"); }else{ //x<z<y A=x; B=z; C=y; } }else{//z<x<y A=z; B=x; C=y; } }else{//y<x if(y<z){ if(x<z){//y<x<z A=y; B=x; C=z; }else{//y<z<x A=y; B=z; C=x; } }else{//z<y<x A=z; B=y; C=x; } } } }

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• Accessing Static Methods on a Generic class in c#

  - by mrlane

  Hello, I have the following situation in code, which I suspect may be a bit dodgey: I have a class: abstract class DataAccessBase<T> : IDataAccess where T : AnotherAbstractClass This class DataAccessBase also has a static factory method which creates instances of derived classes of itself using an enum value in a which statement to decide which derived type to create: static IDataAccess CreateInstance(TypeToCreateEnum) Now, the types derived from DataAccessBase<T> are themselves NOT generic, they specify a type for T: class PoLcZoneData : DataAccessBase<PoLcZone> // PoLcZone is derived from AnotherAbstractClass So far I am not sure if this is pushing the limits of good use of generics, but what I am really concerned about is how to access the static CreateInstance() method in the first place: The way I am doing this at the moment is to simply pass any type T where T : AnotherAbstractClass. In particular I am passing AnotherAbstractClass itself. This allows compilation just fine, but it does seem to me that passing any type to a generic class just to get at the statics is a bit dodgey. I have actually simplified the situation somewhat as DataAccessBase<T> is the lower level in the inheritance chain, but the static factory methods exists in a middle tier with classes such as PoLcZoneData being the most derived on the only level that is not generic. What are peoples thoughts on this arrangement?

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• Thread-safe initialization of function-local static const objects

  - by sbi

  This question made me question a practice I had been following for years. For thread-safe initialization of function-local static const objects I protect the actual construction of the object, but not the initialization of the function-local reference referring to it. Something like this: namspace { const some_type& create_const_thingy() { lock my_lock(some_mutex); static const some_type the_const_thingy; return the_const_thingy; } } void use_const_thingy() { static const some_type& the_const_thingy = create_const_thingy(); // use the_const_thingy } The idea is that locking takes time, and if the reference is overwritten by several threads, it won't matter. I'd be interested if this is safe enough in practice? safe according to The Rules? (I know, the current standard doesn't even know what "concurrency" is, but what about trampling over an already initialized reference? And do other standards, like POSIX, have something to say that's relevant to this?) For the inquiring minds: Many such function-local static const objects I used are maps which are initialized from const arrays upon first use and used for lookup. For example, I have a few XML parsers where tag name strings are mapped to enum values, so I could later switch over the tags enum values.

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• Categories in static library for iPhone device 3.0

  - by Nick

  I have categories in my static library. Any application developer should set -ObjC flag to "Other Linker Flags" to use my static library properly. It works fine for iPhone device/iPhone Simulator 2.x and iPhone Simulator 3.0. But it crashes for iPhone device 3.0. As written in this article it is new linker bug. They suggest to use one more linker flag: -all_load. But when I add this flag, build fails too, because there are duplicate symbols. How to use categories in static libraries for iPhone device 3.0? Any suggestions?

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• .NET: will Random.Random operate differently inside a static method

  - by Craig Johnston

  I am having difficulty with the following code which is inside a static method of a non-static class. int iRand; int rand; rand = new Random((int)DateTime.Now.Ticks); iRand = rand.Next(50000); The iRand number, along with some other values, are being inserted into a new row of an Access MDB table via OLEDB. The iRand number is being inserted into a field that is part of the primary key, and the insert attempt is throwing the following exception even though the iRand number is supposed to be random: System.Data.OleDb.OleDbException: The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again. Could the fact the method is static be making the iRand number stay the same, for some reason?

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• DLL export of a static function

  - by Begbie00

  Hi all - I have the following static function: static inline HandVal StdDeck_StdRules_EVAL_N( StdDeck_CardMask cards, int n_cards ) Can I export this function in a DLL? If so, how? Thanks, Mike Background information: I'm doing this because the original source code came with a VS project designed to compile as a static (.lib) library. In order to use ctypes/Python, I'm converting the project to a DLL. I started a VS project as a DLL and imported the original source code. The project builds into a DLL, but none of the functions (including functions such as the one listed above) are exported (as confirmed by both the absence of dllexport in the source code and tools such as DLL Export Viewer). I tried to follow the general advice here (create an exportable wrapper function within the header) to no avail...functions still don't appear to be exported.

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• accessing a static property via COM

  - by joreg

  is it possible to access a static property of a COM object without creating an instance of the object? my situation is this: i have an unmanaged application (written in delphi). this application exposes a COM-based plugininterface. until now i only wrote managed plugins in c#. plugins provide their info (name, author, ..) via a static property that returns an instance of PluginInfo (which implements IPluginInfo). this static property i can access on the managed plugins using http://managedvcl.com. now i want to write unmanaged plugins on the same interface. i can load them using: plug := CreateComObject(TGuid) as IMyPlugInterface; and they run, but i don't know how to read out their PluginInfo. so the question again is: is there another way than implementing IPluginInfo in the plugin-class and only accessing the info after i have created an instance of the plugin?

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• Java: startingPath as "public static final" exception

  - by HH

  [Updated] Thanks to polygenelubricants's reply, the real problem is the exception from the method getCanonicalPath() because I cannot include try-catch-loop there. $ cat StartingPath.java import java.util.*; import java.io.*; public class StartingPath { public static final String startingPath = (new File(".")).getCanonicalPath(); public static void main(String[] args){ System.out.println(startingPath); } } $ javac StartingPath.java StartingPath.java:5: unreported exception java.io.IOException; must be caught or declared to be thrown public static final String startingPath = (new File(".")).getCanonicalPath(); ^ 1 error

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• Returning in a static initializer

  - by Martijn Courteaux

  Hello, This isn't valid code: public class MyClass { private static boolean yesNo = false; static { if (yesNo) { System.out.println("Yes"); return; // The return statement is the problem } System.exit(0); } } This is a stupid example, but in a static class constructor we can't return;. Why? Are there good reasons for this? Does someone know something more about this? So the reason why I should do return is to end constructing there. Thanks

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• Finding C++ static initialization order problems

  - by Fred Larson

  We've run into some problems with the static initialization order fiasco, and I'm looking for ways to comb through a whole lot of code to find possible occurrences. Any suggestions on how to do this efficiently? Edit: I'm getting some good answers on how to SOLVE the static initialization order problem, but that's not really my question. I'd like to know how to FIND objects that are subject to this problem. Evan's answer seems to be the best so far in this regard; I don't think we can use valgrind, but we may have memory analysis tools that could perform a similar function. That would catch problems only where the initialization order is wrong for a given build, and the order can change with each build. Perhaps there's a static analysis tool that would catch this. Our platform is IBM XLC/C++ compiler running on AIX.

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• Exposing headers on iPhone static library

  - by leolobato

  Hello guys, I've followed this tutorial for setting up a static library with common classes from 3 projects we are working on. It's pretty simple, create a new static library project on xcode, add the code there, a change some headers role from project to public. The tutorial says I should add my library folder to the header search paths recursively. Is this the right way to go? I mean, on my library project, I have files separated in folders like Global/, InfoScreen/, Additions/. I was trying to setup one LOKit.h file on the root folder, and inside that file #import everything I need to expose. So on my host project I don't need to add the folder recursively to the header search path, and would just #import "LOKit.h". But I couldn't get this to work, the host project won't build complaining about all the classes I didn't add to LOKit.h, even though the library project builds. So, my question is, what is the right way of exposing header files when I setup a Cocoa Touch Static Library project on xCode?

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• Returning in a static class constructor

  - by Martijn Courteaux

  Hello, This isn't valid code: public class MyClass { private static boolean yesNo = false; static { if (yesNo) { System.out.println("Yes"); return; // The return statement is the problem } System.exit(0); } } This is a stupid example, but in a static class constructor we can't return;. Why? Are there good reasons for this? Does someone know something more about this? So the reason why I should do return is to end constructing there. Thanks

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• Why is this static routing not working ?

  - by geeko

  Greeting gurus, I'm trying to develop a DHCP enforcement extension like Microsoft NAP. My trick to block dynamic-IP requesting machines (that don't meet certain policy) is to strip the default gateway (no default gateway) stated in the IP lease and set the lease subnet mask to 255.255.255.255. Now I need the blocked machines to be able to reach some specific locations (IPs) on the network. To allow for this, I'm including some static routes in the lease. For example, I'm including 10.10.10.11 via router 10.10.10.254 (the one to which the blocked machine that needs to access 10.10.10.11 is connected). Unfortunately, as soon as I set the default gateway to nothing, blocked machines cannot reach any of the added static routes. I also tried classless static routes. Any ideas ? any one knows how MS NAP actually do it ? Geeko

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• Static struct in C++

  - by pingvinus

  Hi, I want to define an structure, where some math constants would be stored. Here what I've got now: struct consts { //salt density kg/m3 static const double gamma; }; const double consts::gamma = 2350; It works fine, but there would be more than 10 floating point constants, so I doesn't want to wrote 'static const' before each of them. And define something like that: static const struct consts { //salt density kg/m3 double gamma; }; const double consts::gamma = 2350; It look fine, but I got these errors: 1. member function redeclaration not allowed 2. a nonstatic data member may not be defined outside its class I wondering if there any C++ way to do it?

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• c++ defining a static member of a template class with type inner class pointer

  - by Jack

  I have a template class like here (in a header) with a inner class and a static member of type pointer to inner class template <class t> class outer { class inner { int a; }; static inner *m; }; template <class t> outer <t>::inner *outer <t>::m; when i want to define that static member i says "error: expected constructor, destructor, or type conversion before '*' token" on the last line (mingw32-g++ 3.4.5)

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• C++ Class Static variable problem - C programmer new to C++

  - by Microkernel

  Hi guys, I am a C programmer, but had learnt C++ @school longtime back. Now I am trying to write code in C++ but getting compiler error. Please check and tell me whats wrong with my code. typedef class _filter_session { private: static int session_count; /* Number of sessions count -- Static */ public: _filter_session(); /* Constructor */ ~_filter_session(); /* Destructor */ }FILTER_SESSION; _filter_session::_filter_session(void) { (this->session_count)++; return; } _filter_session::~_filter_session(void) { (this->session_count)--; return; } The error that I am getting is "error LNK2001: unresolved external symbol "private: static int _filter_session::session_count" (?session_count@_filter_session@@0HA)" I am using Visual Studio 2005 by the way. Plz plz help me. Regards, Microkernel

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• static setter method injection in Spring

  - by vishnu

  Hi, I have following requirement I wanted to pass http:\\localhost:9080\testws.cls value as setter injection through spring configuration file. How can i do this static variable setter injection for WSDL_LOCATION public class Code1 extends javax.xml.ws.Service { private final static URL CODE1_WSDL_LOCATION; static { URL url = null; try { url = new URL("http:\\localhost:9080\testws.cls"); } catch (MalformedURLException e) { e.printStackTrace(); } CODE1_WSDL_LOCATION = url; } public Code1(URL wsdlLocation, QName serviceName) { super(wsdlLocation, serviceName); } public Code1() { super(CODE1_WSDL_LOCATION, new QName("http://tempuri.org", "Code1")); } /** * * @return * returns Code1Soap */ @WebEndpoint(name = "Code1Soap") public Code1Soap getCode1Soap() { return (Code1Soap)super.getPort(new QName("http://tempuri.org", "Code1Soap"), Code1Soap.class); } } Please help me out.

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• Difference between static const char* and const char*.

  - by Will MacDonagh

  Could someone please explain the difference in how the 2 snippets of code are handled below? They definitely compile to different assembly code, but I'm trying to understand how the code might act differently. I understand that string literals are thrown into read only memory and are effectively static, but how does that differ from the explicit static below? struct Obj1 { void Foo() { const char* str( "hello" ); } }; and struct Obj2 { void Bar() { static const char* str( "hello" ); } };

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• default value for a static property

  - by Blitzz

  I like c#, but why can I do : public static bool Initialized { private set; get; } or this : public static bool Initialized = false; but not a mix of both in one line ? I just need to set access level to my variable (private set), and I need it set at false on startup. I wouldn't like to make that boring private _Initialized variable, which would be returned by the getter of the public Initialized var. I like my code to be beautiful. (NB: my variable is static, it can't be initialized in the constructor). Thanks

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