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• What is the fastest way to do division in C for 8bit MCUs?

  - by Jordan S

  I am working on the firmware for a device that uses an 8bit mcu (8051 architecture). I am using SDCC (Small Device C Compiler). I have a function that I use to set the speed of a stepper motor that my circuit is driving. The speed is set by loading a desired value into the reload register for a timer. I have a variable, MotorSpeed that is in the range of 0 to 1200 which represents pulses per second to the motor. My function to convert MotorSpeed to the correct 16bit reload value is shown below. I know that float point operations are pretty slow and I am wondering if there is a faster way of doing this... void SetSpeed() { float t = MotorSpeed; unsigned int j = 0; t = 1/t ; t = t / 0.000001; j = MaxInt - t; TMR3RL = j; // Set reload register for desired freq return; }

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• Would an immutable keyword in Java be a good idea?

  - by berry120

  Generally speaking, the more I use immutable objects in Java the more I'm thinking they're a great idea. They've got lots of advantages from automatically being thread-safe to not needing to worry about cloning or copy constructors. This has got me thinking, would an "immutable" keyword go amiss? Obviously there's the disadvantages with adding another reserved word to the language, and I doubt it will actually happen primarily for the above reason - but ignoring that I can't really see many disadvantages. At present great care has to be taken to make sure objects are immutable, and even then a dodgy javadoc comment claiming a component object is immutable when it's in fact not can wreck the whole thing. There's also the argument that even basic objects like string aren't truly immutable because they're easily vunerable to reflection attacks. If we had an immutable keyword the compiler could surely recursively check and give an iron clad guarantee that all instances of a class were immutable, something that can't presently be done. Especially with concurrency becoming more and more used, I personally think it'd be good to add a keyword to this effect. But are there any disadvantages or implementation details I'm missing that makes this a bad idea?

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• What's a good way to make a Flex component with placeholders in it?

  - by Daniel Brockman

  I want to create a component that has a couple of "holes" that are to be filled in differently on each use. Currently, I'm doing it like this (using the Flex 4 framework in this example --- it would look almost the same for Flex 3): public var fooComponent : IVisualElement; public var barComponent : IVisualElement; override protected function createChildren() : void { super.createChildren(); fooContainer.addElement(fooComponent); barContainer.addElement(barComponent); } <Group id="fooContainer"/> <!-- ... other components ... --> <Group id="barContainer"/> This works well, but it's kind of a lot of code to write for something so simple. What I'd like is something like this: [Bindable] public var fooComponent : IVisualElement; [Bindable] public var barComponent : IVisualElement; <Placeholder content="{fooComponent}"/> <!-- ... other components ... --> <Placeholder content="{barComponent}"/> Now, I could implement the Placeholder component myself, but I can't help wondering if there isn't a better way to do this using the existing tools in the Flex framework. Theoretically, with the proper compiler support, it could even be boiled down to something like this: <Placeholder id="fooComponent"/> <!-- ... other components ... --> <Placeholder id="barComponent"/>

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• Does C# allow method overloading, PHP style (__call)?

  - by mr.b

  In PHP, there is a special method named __call($calledMethodName, $arguments), which allows class to catch calls to non-existing methods, and do something about it. Since most of classic languages are strongly typed, compiler won't allow calling a method that does not exist, I'm clear with that part. What I want to accomplish (and I figured this is how I would do it in PHP, but C# is something else) is to proxy calls to a class methods and log each of these calls. Right now, I have code similar to this: class ProxyClass { static logger; public AnotherClass inner { get; private set; } public ProxyClass() { inner = new AnotherClass(); } } class AnotherClass { public void A() {} public void B() {} public void C() {} // ... } // meanwhile, in happyCodeLandia... ProxyClass pc = new ProxyClass(); pc.inner.A(); pc.inner.B(); // ... So, how can I proxy calls to an object instance in extensible way? Extensible, meaning that I don't have to modify ProxyClass whenever AnotherClass changes. In my case, AnotherClass can have any number of methods, so it wouldn't be appropriate to overload or wrap all methods to add logging. I am aware that this might not be the best approach for this kind of problem, so if anyone has idea what approach to use, shoot. Thanks!

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• multiple definition in header file

  - by Jérôme

  Here is a small code-example from which I'd like to ask a question : complex.h : #ifndef COMPLEX_H #define COMPLEX_H #include <iostream> class Complex { public: Complex(float Real, float Imaginary); float real() const { return m_Real; }; private: friend std::ostream& operator<<(std::ostream& o, const Complex& Cplx); float m_Real; float m_Imaginary; }; std::ostream& operator<<(std::ostream& o, const Complex& Cplx) { return o << Cplx.m_Real << " i" << Cplx.m_Imaginary; } #endif // COMPLEX_H complex.cpp : #include "complex.h" Complex::Complex(float Real, float Imaginary) { m_Real = Real; m_Imaginary = Imaginary; } main.cpp : #include "complex.h" #include <iostream> int main() { Complex Foo(3.4, 4.5); std::cout << Foo << "\n"; return 0; } When compiling this code, I get the following error : multiple definition of operator<<(std::ostream&, Complex const&) I've found that making this fonction inline solves the problem, but I don't understand why. Why does the compiler complain about multiple definition ? My header file is guarded (with #define COMPLEX_H). And, if complaining about the operator<< fonction, why not complain about the public real() fonction, which is defined in the header as well ? And is there another solution as using the inline keyword ?

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• How can I modified the value of a string defined in a struc?

  - by Eric

  Hi, I have the following code in c++: define TAM 4000 define NUMPAGS 512 struct pagina { bitset<12 direccion; char operacion; char permiso; string *dato; int numero; }; void crearPagina(pagina* pag[], int pos, int dir) { pagina * paginas = (pagina*)malloc(sizeof(char) * TAM); paginas - direccion = bitset<12 (dir); paginas - operacion = 'n'; paginas - permiso = 'n'; string **tempDato = &paginas - dato; char *temp = " "; **tempDato = temp; paginas - numero = 0; pag[pos] = paginas; } I want to modify the value of the variable called "string *dato" in the struct pagina but, everytime I want to assing a new value, the compiler throws a segmentation fault. In this case I'm using a pointer to string, but I have also tried with a string. In a few words I want to do the following: pagina - dato = "test"; Any idea? Thanks in advance!!!

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• What are the lengths/limits C preprocessor as a language creation tool? Where can I learn more about

  - by Weston C

  In his FAQ @ http://www2.research.att.com/~bs/bs_faq.html#bootstrapping, Bjarne Stroustrup says: To build [Cfront, the first C++ compiler], I first used C to write a "C with Classes"-to-C preprocessor. "C with Classes" was a C dialect that became the immediate ancestor to C++... I then wrote the first version of Cfront in "C with Classes". When I read this, it piqued my interest in the C preprocessor. I'd seen its macro capabilities as suitable for simplifying common expressions but hadn't thought about its ability to significantly add to syntax and semantics on the level that I imagine bringing classes to C took. So now I have a couple of questions on my mind: 1) Are there other examples of this approach to bootstrapping a language off of C? 2) Is the source to Stroustrup's original work available anywhere? 3) Where could I learn more about the specifics of utilizing this technique? 4) What are the lengths/limits of that approach? Could one, say, create a set of preprocessor macros that let someone write in something significantly Lisp/Scheme like?

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• Why is Func<T> ambiguous with Func<IEnumerable<T>>?

  - by Matt Hamilton

  This one's got me flummoxed, so I thought I'd ask here in the hope that a C# guru can explain it to me. Why does this code generate an error? class Program { static void Main(string[] args) { Foo(X); // the error is on this line } static String X() { return "Test"; } static void Foo(Func<IEnumerable<String>> x) { } static void Foo(Func<String> x) { } } The error in question: Error 1 The call is ambiguous between the following methods or properties: 'ConsoleApplication1.Program.Foo(System.Func<System.Collections.Generic.IEnumerable<string>>)' and 'ConsoleApplication1.Program.Foo(System.Func<string>)' C:\Users\mabster\AppData\Local\Temporary Projects\ConsoleApplication1\Program.cs 12 13 ConsoleApplication1 It doesn't matter what type I use - if you replace the "String" declarations with "int" in that code you'll get the same sort of error. It's like the compiler can't tell the difference between Func<T> and Func<IEnumerable<T>>. Can someone shed some light on this?

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• Run arbitrary subprocesses on Windows and still terminate cleanly?

  - by Weeble

  I have an application A that I would like to be able to invoke arbitrary other processes as specified by a user in a configuration file. Batch script B is one such process a user would like to be invoked by A. B sets up some environment variables, shows some messages and invokes a compiler C to do some work. Does Windows provide a standard way for arbitrary processes to be terminated cleanly? Suppose A is run in a console and receives a CTRL+C. Can it pass this on to B and C? Suppose A runs in a window and the user tries to close the window, can it cancel B and C? TerminateProcess is an option, but not a very good one. If A uses TerminateProcess on B, C keeps running. This could cause nasty problems if C is long-running, since we might start another instance of C to operate on the same files while the first instance of C is still secretly at work. In addition, TerminateProcess doesn't result in a clean exit. GenerateConsoleCtrlEvent sounds nice, and might work when everything's running in a console, but the documentation says that you can only send CTRL+C to your own console, and so wouldn't help if A were running in a window. Is there any equivalent to SIGINT on Windows? I would love to find an article like this one: http://www.cons.org/cracauer/sigint.html for Windows.

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• LuaEdit can't find module when Lua files all in the same folder

  - by joverboard

  I downloaded LuaEdit to use as an IDE and debug tool however I'm having trouble using it for even the simplest things. I've created a solution with 2 files in it, all of which are stored in the same folder. My files are as follows: --startup.lua require("foo") test("Testing", "testing", "one, two, three") --foo.lua foo = {} print("In foo.lua") function test(a,b,c) print(a,b,c) end This works fine when in my C++ compiler when accessed through some embed code, however when I attempt to use the same code in LuaEdit, it crashes on line 3 require("foo") with an error stating: module 'foo' not found: no field package.preload['foo'] no file 'C:\Program Files (x86)\LuaEdit 2010\lua\foo.lua' no file 'C:\Program Files (x86)\LuaEdit 2010\lua\foo\init.lua' no file 'C:\Program Files (x86)\LuaEdit 2010\foo.lua' no file 'C:\Program Files (x86)\LuaEdit 2010\foo\init.lua' no file '.\foo.lua' no file 'C:\Program Files (x86)\LuaEdit 2010\foo.dll' no file 'C:\Program Files (x86)\LuaEdit 2010\loadall.dll' no file '.\battle.dll' I have also tried creating these files prior to adding them to a solution and still get the same error. Is there some setting I'm missing? It would be great to have an IDE/debugger but it's useless to me if it can't run linked functions.

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• final transient fields and serialization

  - by doublep

  Is it possible to have final transient fields that are set to any non-default value after serialization in Java? My usecase is a cache variable — that's why it is transient. I also have a habit of making Map fields that won't be changed (i.e. contents of the map is changed, but object itself remains the same) final. However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but null after unserialization. I tried the following, without success: simple field initialization (shown in the example): this is what I normally do, but the initialization doesn't seem to happen after unserialization; initialization in constructor (I believe this is semantically the same as above though); assigning the field in readObject() — cannot be done since the field is final. In the example cache is public only for testing. import java.io.*; import java.util.*; public class test { public static void main (String[] args) throws Exception { X x = new X (); System.out.println (x + " " + x.cache); ByteArrayOutputStream buffer = new ByteArrayOutputStream (); new ObjectOutputStream (buffer).writeObject (x); x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject (); System.out.println (x + " " + x.cache); } public static class X implements Serializable { public final transient Map <Object, Object> cache = new HashMap <Object, Object> (); } } Output: test$X@1a46e30 {} test$X@190d11 null

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• Java Generics Class Type Parameter Inference

  - by Pindatjuh

  Given the interface: public interface BasedOnOther<T, U extends BasedList<T>> { public T getOther(); public void staticStatisfied(final U list); } The BasedOnOther<T, U extends BasedList<T>> looks very ugly in my use-cases. It is because the T type parameter is already defined in the BasedList<T> part, so the "uglyness" comes from that T needs to be typed twice. Problem: is it possible to let the Java compiler infer the generic T type from BasedList<T> in a generic class/interface definition? Ultimately, I'd like to use the interface like: class X extends BasedOnOther<BasedList<SomeType>> { public SomeType getOther() { ... } public void staticStatisfied(final BasedList<SomeType> list) { ... } } Instead: class X extends BasedOnOther<SomeType, BasedList<SomeType>> { public SomeType getOther() { ... } public void staticStatisfied(final BasedList<SomeType> list) { ... } }

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• not able to run c/cpp execs in eclipse cdt

  - by user1658323

  i installed eclipse and then cdt on an ubuntu system recently and was trying to make the first runnable c/c++ proj.. i installed g++ also, and then created the first executable cpp 'Hello World' project some files are created... then some issues... 1) even though Build Automatically is selected, I have to goto the project n do a Build Project to build it manually, and this i have to do everytime i make a change 2) After Building manually, there are some new folders created with Binaries and Debug files and i can see g++ commands in the console being executed. The project binary is output both to debug n binaries folder. But i am not able to run these through the Green Play Button or any other way in eclipse. Even Run configuration is not showing any option for c/C++ proj.. though i can goto terminal and run the binary myself through ./ But i want to be able to run n debug this through eclipse. plz help in fixing me this problem as i really love eclipse n have some c/cpp assignments coming soon.. Console info on doing a manual project build - Build of configuration Debug for project qwe ** make all Building file: ../src/qwe.cpp Invoking: GCC C++ Compiler g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/qwe.d" -MT"src/qwe.d" -o "src/qwe.o" "../src/qwe.cpp" Finished building: ../src/qwe.cpp Building target: qwe Invoking: GCC C++ Linker g++ -o "qwe" ./src/qwe.o Finished building target: qwe Build Finished **

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• Does it ever make sense to make a fundamental (non-pointer) parameter const?

  - by Scott Smith

  I recently had an exchange with another C++ developer about the following use of const: void Foo(const int bar); He felt that using const in this way was good practice. I argued that it does nothing for the caller of the function (since a copy of the argument was going to be passed, there is no additional guarantee of safety with regard to overwrite). In addition, doing this prevents the implementer of Foo from modifying their private copy of the argument. So, it both mandates and advertises an implementation detail. Not the end of the world, but certainly not something to be recommended as good practice. I'm curious as to what others think on this issue. Edit: OK, I didn't realize that const-ness of the arguments didn't factor into the signature of the function. So, it is possible to mark the arguments as const in the implementation (.cpp), and not in the header (.h) - and the compiler is fine with that. That being the case, I guess the policy should be the same for making local variables const. One could make the argument that having different looking signatures in the header and source file would confuse others (as it would have confused me). While I try to follow the Principle of Least Astonishment with whatever I write, I guess it's reasonable to expect developers to recognize this as legal and useful.

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• Why does GCC need extra declarations in templates when VS does not?

  - by Kyle

  template<typename T> class Base { protected: Base() {} T& get() { return t; } T t; }; template<typename T> class Derived : public Base<T> { public: Base<T>::get; // Line A Base<T>::t; // Line B void foo() { t = 4; get(); } }; int main() { return 0; } If I comment out lines A and B, this code compiles fine under Visual Studio 2008. Yet when I compile under GCC 4.1 with lines A and B commented, I get these errors: In member function ‘void TemplateDerived::foo()’: error: ‘t’ was not declared in this scope error: there are no arguments to ‘get’ that depend on a template parameter, so a declaration of ‘get’ must be available Why would one compiler require lines A and B while the other doesn't? Is there a way to simplify this? In other words, if derived classes use 20 things from the base class, I have to put 20 lines of declarations for every class deriving from Base! Is there a way around this that doesn't require so many declarations?

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• Extending the method pool of a concrete class which is derived by an interface

  - by CelGene

  Hello, I had created an interface to abstract a part of the source for a later extension. But what if I want to extend the derived classes with some special methods? So I have the interface here: class virtualFoo { public: virtual ~virtualFoo() { } virtual void create() = 0; virtual void initialize() = 0; }; and one derived class with an extra method: class concreteFoo : public virtualFoo { public: concreteFoo() { } ~concreteFoo() { } virtual void create() { } virtual void initialize() { } void ownMethod() { } }; So I try to create an Instance of concreteFoo and try to call ownMethod like this: void main() { virtualFoo* ptr = new concreteFoo(); concreteFoo* ptr2 = dynamic_cast(ptr); if(NULL != ptr2) ptr2->ownMethod(); } It works but is not really the elegant way. If I would try to use ptr-ownMethod(); directly the compiler complains that this method is not part of virtualFoo. Is there a chance to do this without using dynamic_cast? Thanks in advance!

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• User defined literal arguments are not constexpr?

  - by Pubby

  I'm testing out user defined literals. I want to make _fac return the factorial of the number. Having it call a constexpr function works, however it doesn't let me do it with templates as the compiler complains that the arguments are not and cannot be constexpr. I'm confused by this - aren't literals constant expressions? The 5 in 5_fac is always a literal that can be evaluated during compile time, so why can't I use it as such? First method: constexpr int factorial_function(int x) { return (x > 0) ? x * factorial_function(x - 1) : 1; } constexpr int operator "" _fac(unsigned long long x) { return factorial_function(x); // this works } Second method: template <int N> struct factorial { static const unsigned int value = N * factorial<N - 1>::value; }; template <> struct factorial<0> { static const unsigned int value = 1; }; constexpr int operator "" _fac(unsigned long long x) { return factorial_template<x>::value; // doesn't work - x is not a constexpr }

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• Native Endians and Auto Conversion

  - by KnickerKicker

  so the following converts big endians to little ones uint32_t ntoh32(uint32_t v) { return (v << 24) | ((v & 0x0000ff00) << 8) | ((v & 0x00ff0000) >> 8) | (v >> 24); } works. like a charm. I read 4 bytes from a big endian file into char v[4] and pass it into the above function as ntoh32 (* reinterpret_cast<uint32_t *> (v)) that doesn't work - because my compiler (VS 2005) automatically converts the big endian char[4] into a little endian uint32_t when I do the cast. AFAIK, this automatic conversion will not be portable, so I use uint32_t ntoh_4b(char v[]) { uint32_t a = 0; a |= (unsigned char)v[0]; a <<= 8; a |= (unsigned char)v[1]; a <<= 8; a |= (unsigned char)v[2]; a <<= 8; a |= (unsigned char)v[3]; return a; } yes the (unsigned char) is necessary. yes it is dog slow. there must be a better way. anyone ?

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• How do I implement configurations and settings?

  - by Malvolio

  I'm writing a system that is deployed in several places and each site needs its own configurations and settings. A "configuration" is a named value that is necessary to a particular site (e.g., the database URL, S3 bucket name); every configuration is necessary, there is not usually a default, and it's typically string-valued. A setting is a named value but it just tweaks the behavior of the system; it's often numeric or Boolean, and there's usually some default. So far, I've been using property files or thing like them, but it's a terrible solution. Several times, a developer has added a requirement for a configuration but not added the value to file for the live configuration, so the new release passed all the tests, then failed when released to live. Better, of course, for every file to be compiled — so if there's a missing configuration, or one of the wrong type, it won't get past the compiler — and inject the site-specific class into the build for each site. As a bones, a Scala file can easy model more complex values, especially lists, but also maps and tuples. The downside is, the files are sometimes maintained by people who aren't developers, so it has to be pretty self-explanatory, which was the advantage of property files. (Someone explain XML configurations to me: all the complexity of a compilable file but the run-time risk of a property file.) What I'm looking for is an easy pattern for defining a group required names and allowable values. Any suggestions?

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• Resources and techniques/methods for SCJP preparation ?

  - by BenoitParis

  I am passing the SCJP 6 exam in a month. I have the "SCJP Sun Certified Programmer for Java 6 Exam 310-065" book. It seems great for the exam. But I want your advice on this. Getting the closest possible to 100% would be great. I have found a site that answered some of the questions you ask yourself when you go trough the book. Here is it : http://www.janeg.ca/java2.html As you can see it was written for Java 2 :/ I have written another specific question here on StackOverflow about the usefulness of JVM specification and Java compiler code for the SCJP. Will Update the results here. Here it is. Please share the resources you used in preparing the exam. Please also specify any resources that you think might help. Any type of resource is welcome: books, code, specs, sites, wikies, papers, online tests, grandmas... Please also share on any method/technique that helped you prepare the exam. Please also comment on the return you got from the resource and the method (for the learning process and for points in the exam) I'll begin: Book : "SCJP Sun Certified Programmer for Java 6 Exam 310-065". Seems like the official book for the preparation. Technique : Writing code in a text editor and compiling it with javac to test a question. NO IDEs! It helps you get a a straight answer to a question you have. It helps you pay attention to every word in the code (and this is very important in the SCJP) EDIT: Added dimension: Are there good, up-to-date online tests?

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• Can C++ do something like an ML case expression?

  - by Nathan Andrew Mullenax

  So, I've run into this sort of thing a few times in C++ where I'd really like to write something like case (a,b,c,d) of (true, true, _, _ ) => expr | (false, true, _, false) => expr | ... But in C++, I invariably end up with something like this: bool c11 = color1.count(e.first)>0; bool c21 = color2.count(e.first)>0; bool c12 = color1.count(e.second)>0; bool c22 = color2.count(e.second)>0; // no vertex in this edge is colored // requeue if( !(c11||c21||c12||c22) ) { edges.push(e); } // endpoints already same color // failure condition else if( (c11&&c12)||(c21&&c22) ) { results.push_back("NOT BICOLORABLE."); return true; } // nothing to do: nodes are already // colored and different from one another else if( (c11&&c22)||(c21&&c12) ) { } // first is c1, second is not set else if( c11 && !(c12||c22) ) { color2.insert( e.second ); } // first is c2, second is not set else if( c21 && !(c12||c22) ) { color1.insert( e.second ); } // first is not set, second is c1 else if( !(c11||c21) && c12 ) { color2.insert( e.first ); } // first is not set, second is c2 else if( !(c11||c21) && c22 ) { color1.insert( e.first ); } else { std::cout << "Something went wrong.\n"; } I'm wondering if there's any way to clean all of those if's and else's up, as it seems especially error prone. It would be even better if it were possible to get the compiler complain like SML does when a case expression (or statement in C++) isn't exhaustive. I realize this question is a bit vague. Maybe, in sum, how would one represent an exhaustive truth table with an arbitrary number of variables in C++ succinctly? Thanks in advance.

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• How are two-dimensional arrays formatted in memory?

  - by Chris Cooper

  In C, I know I can dynamically allocate a two-dimensional array on the heap using the following code: int** someNumbers = malloc(arrayRows*sizeof(int*)); for (i = 0; i < arrayRows; i++) { someNumbers[i] = malloc(arrayColumns*sizeof(int)); } Clearly, this actually creates a one-dimensional array of pointers to a bunch of separate one-dimensional arrays of integers, and "The System" can figure you what I mean when I ask for: someNumbers[4][2]; But when I statically declare a 2D array, as in the following line...: int someNumbers[ARRAY_ROWS][ARRAY_COLUMNS]; ...does a similar structure get created on the stack, or is it of another form completely? (i.e. is it a 1D array of pointers? If not, what is it, and how do references to it get figured out?) Also, when I said, "The System," what is actually responsible for figuring that out? The kernel? Or does the C compiler sort it out while compiling?

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• Delphi: How to avoid EIntOverflow underflow when subtracting?

  - by Ian Boyd

  Microsoft already says, in the documentation for GetTickCount, that you could never compare tick counts to check if an interval has passed. e.g.: Incorrect (pseudo-code): DWORD endTime = GetTickCount + 10000; //10 s from now ... if (GetTickCount > endTime) break; The above code is bad because it is suceptable to rollover of the tick counter. For example, assume that the clock is near the end of it's range: endTime = 0xfffffe00 + 10000 = 0x00002510; //9,488 decimal Then you perform your check: if (GetTickCount > endTime) Which is satisfied immediatly, since GetTickCount is larger than endTime: if (0xfffffe01 > 0x00002510) The solution Instead you should always subtract the two time intervals: DWORD startTime = GetTickCount; ... if (GetTickCount - startTime) > 10000 //if it's been 10 seconds break; Looking at the same math: if (GetTickCount - startTime) > 10000 if (0xfffffe01 - 0xfffffe00) > 10000 if (1 > 10000) Which is all well and good in C/C++, where the compiler behaves a certain way. But what about Delphi? But when i perform the same math in Delphi, with overflow checking on ({Q+}, {$OVERFLOWCHECKS ON}), the subtraction of the two tick counts generates an EIntOverflow exception when the TickCount rolls over: if (0x00000100 - 0xffffff00) > 10000 0x00000100 - 0xffffff00 = 0x00000200 What is the intended solution for this problem? Edit: i've tried to temporarily turn off OVERFLOWCHECKS: {$OVERFLOWCHECKS OFF}] delta = GetTickCount - startTime; {$OVERFLOWCHECKS ON} But the subtraction still throws an EIntOverflow exception. Is there a better solution, involving casts and larger intermediate variable types?

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• Foreign key relationships in Entity Framework

  - by Anders Svensson

  I'm trying to add an object created from Entity Data Model classes. I have a table called Users, which has turned into a User EDM class. And I also have a table Pages, which has become a Page EDM class. These tables have a foreign key relationship, so that each page is associated with many users. Now I want to be able to add a page, but I can't get how to do it. I get a nullreference exception on Users below. I'm still rather confused by all this, so I'm sure it's a simple error, but I just can't see how to do it. Also, by the way, the compiler requires that I set PageID in the object initializer, even though this field is set to be an automatic id in the table. Am I doing it right just setting it to 0, expecting it to be updated automatically in the table when saved, or how should I do that? Any help appreciated! The method in question: private Page GetPage(User currentUser) { string url = _request.ServerVariables["url"].ToLower(); var userPages = from p in _context.PageSet where p.Users.UserID == currentUser.UserID select p; var existingPage = userPages.FirstOrDefault(e => e.Url == url); //Could be combined with above, but hard to read? if (existingPage != null) return existingPage; Page page = new Page() { Count = 0, Url = _request.ServerVariables["url"].ToLower(), PageID = 0, //Only initial value, changed later? }; _context.AddToPageSet(page); page.Users.UserID = currentUser.UserID; //Here's the problem... return page; }

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• Using child visitor in C#

  - by Thomas Matthews

  I am setting up a testing component and trying to keep it generic. I want to use a generic Visitor class, but not sure about using descendant classes. Example: public interface Interface_Test_Case { void execute(); void accept(Interface_Test_Visitor v); } public interface Interface_Test_Visitor { void visit(Interface_Test_Case tc); } public interface Interface_Read_Test_Case : Interface_Test_Case { uint read_value(); } public class USB_Read_Test : Interface_Read_Test_Case { void execute() { Console.WriteLine("Executing USB Read Test Case."); } void accept(Interface_Test_Visitor v) { Console.WriteLine("Accepting visitor."); } uint read_value() { Console.WriteLine("Reading value from USB"); return 0; } } public class USB_Read_Visitor : Interface_Test_Visitor { void visit(Interface_Test_Case tc) { Console.WriteLine("Not supported Test Case."); } void visit(Interface_Read_Test_Case rtc) { Console.WriteLine("Not supported Read Test Case."); } void visit(USB_Read_Test urt) { Console.WriteLine("Yay, visiting USB Read Test case."); } } // Code fragment USB_Read_Test test_case; USB_Read_Visitor visitor; test_case.accept(visitor); What are the rules the C# compiler uses to determine which of the methods in USB_Read_Visitor will be executed by the code fragment? I'm trying to factor out dependencies of my testing component. Unfortunately, my current Visitor class contains visit methods for classes not related to the testing component. Am I trying to achieve the impossible?

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