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  • Is typeid of type name always evaluated at compile time in c++ ?

    - by cyril42e
    I wanted to check that typeid is evaluated at compile time when used with a type name (ie typeid(int), typeid(std::string)...). To do so, I repeated in a loop the comparison of two typeid calls, and compiled it with optimizations enabled, in order to see if the compiler simplified the loop (by looking at the execution time which is 1us when it simplifies instead of 160ms when it does not). And I get strange results, because sometimes the compiler simplifies the code, and sometimes it does not. I use g++ (I tried different 4.x versions), and here is the program: #include <iostream> #include <typeinfo> #include <time.h> class DisplayData {}; class RobotDisplay: public DisplayData {}; class SensorDisplay: public DisplayData {}; class RobotQt {}; class SensorQt {}; timespec tp1, tp2; const int n = 1000000000; int main() { int avg = 0; clock_gettime(CLOCK_REALTIME, &tp1); for(int i = 0; i < n; ++i) { // if (typeid(RobotQt) == typeid(RobotDisplay)) // (1) compile time // if (typeid(SensorQt) == typeid(SensorDisplay)) // (2) compile time if (typeid(RobotQt) == typeid(RobotDisplay) || typeid(SensorQt) == typeid(SensorDisplay)) // (3) not compile time ???!!! avg++; else avg--; } clock_gettime(CLOCK_REALTIME, &tp2); std::cout << "time (" << avg << "): " << (tp2.tv_sec-tp1.tv_sec)*1000000000+(tp2.tv_nsec-tp1.tv_nsec) << " ns" << std::endl; } The conditions in which this problem appear are not clear, but: - if there is no inheritance involved, no problem (always compile time) - if I do only one comparison, no problem - the problem only appears only with a disjunction of comparisons if all the terms are false So is there something I didn't get with how typeid works (is it always supposed to be evaluated at compilation time when used with type names?) or may this be a gcc bug in evaluation or optimization? About the context, I tracked down the problem to this very simplified example, but my goal is to use typeid with template types (as partial function template specialization is not possible). Thanks for your help!

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  • C struct memory layout?

    - by Eonil
    I have C# background. Very newbie to low level language like C. In C#, memory layout by compiler by default, and I have to specify some special attribute to override this behavior for exact layout. As I know, C does not re-align by default. But I heard there's a little re-aligning behavior which very hard to find. Can I know about C's memory layout behavior? (what should be re-aligned and not)

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  • [Visual C++]Forcing memory alignment of variables/data-structures

    - by John
    I'm looking at using SSE and I gather aligning data on 16byte boundaries is recommended. There are two cases to consider: float data[4]; struct myystruct { float x,y,z,w; }; I'm not sure the first case can be done explicitly, though there's perhaps a compiler option I could use? In the second case I remember being able to control packing in old versions of GCC several years back, is this still possible?

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  • Undefined reference to `xlCreateBookCA' C++

    - by Jake88
    Hey, I'm trying to use the Libxl library in my eclipse c/c++ project. Right now I'm using the minGW compiler in eclipse. With this following code: Book* book = xlCreateBook(); I get this error: /src/xls2csv.cpp:22: undefined reference to `xlCreateBookCA' Any help would be greatly appreciated :)

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  • Sun's JVM instruction speed table

    - by Pindatjuh
    Is there a benchmark available how much relative time each instruction costs in a single-thread, average-case scenario (either with or without JIT compiler), for the JVM (any version) by Sun? If there is not a benchmark already available, how can I get this information? E.g.: TIME iload_1 1 iadd 12 getfield 40 etc. Where getfield is equivalent to 40 iload_1 instructions.

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  • What does an object file contain

    - by benjamin button
    HI everyone, during the various stages of compilation in C or C++, i know that an object file gets generated. i.e., any_name.o file. what does thos .o file contain actually. i cant open it since its a binary file. Could anybody please help me? are the contents of the object file mainly Dependant on the compiler which we use on unix?

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  • Deriving a class from an abstract class (C++)

    - by cemregoksu
    I have an abstract class with a pure virtual function f() and i want to create a class inherited from that class, and also override function f(). I seperated the header file and the cpp file. I declared the function f(int) in the header file and the definition is in the cpp file. However, the compiler says the derived class is still abstract. How can i fix it?

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  • PowerBuilder 11.5 .NET DLL pbl

    - by RepDetec
    I have converted a PowerBuilder application to 11.5 .NET. When it builds, it compiles into a DLL, an EXE and a bunch of “netmodule” files. Are the netmodules necessary for deployment, or just part of some intermediate step? Is there any way to get the compiler to build me one DLL for each pbl (PowerBuilder library)?

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  • error prepareForSegue between a viewController and a tableViewController

    - by beta
    -(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender { if ([segue.identifier isEqualToString:@"My_TableView"]) { MyTableViewController *destViewController = segue.destinationViewController; destViewController.data = data; } } Hi, I have a problem doing a segue (modal) between a ViewController to a TableViewController. The name of the segue between the ViewController and the NavigationController is "My_TableView". Compiler gives me this error: unrecognized selector sent to instance 0x9275b50 what's the problem?

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  • What does "Contract can't be in try block" mean?

    - by MatthewMartin
    I'm using the 3.5 library for microsoft code contracts public object RetrieveById(int Id) { Contract.Ensures(newObject != null, "object must not be null"); return newProject; //No error message if I move the Contract.Ensures to here //But it isn't asserting/throwing a contract exception here either } I get the compiler message: "Error 18 Contract section within try block in method 'Controller.RetrieveById(System.Int32)'

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  • Is there a C# equivalent of typeof for properties/methods/members?

    - by David
    A classes Type metadata can be obtained in several ways. Two of them are: var typeInfo = Type.GetType("MyClass") and var typeInfo = typeof(MyClass) The advantage of the second way is that typos will be caught by the compiler, and the IDE can understand what I'm talking about (allowing features like refactoring to work without silently breaking the code) Does there exist an equivalent way of strongly referencing members/properties/methods for metadata and reflection? Can I replace: var propertyInfo = typeof(MyClass).GetProperty("MyProperty") with something like: var propertyInfo = property(MyClass.MyProperty)

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  • Compiling in g++ for gprof

    - by myahya
    I do not understand the documentation for gprof regarding how to compile your program for profiling with gprof. In g++, is it required to compile with the -g option (debugging information) in a addition to the -pg option or not. In each case I get different results, and I would like to see where the bottlenecks in my application are in release mode, not in debug mode, where many optimizations are left out by the compiler (e.g. inlining)

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  • How do i detect the deprecated methods in a program?

    - by manus91
    I've searched through the web and what I've found out is this: To make the compiler warn you of the details of which methods you used that were deprecated use the javac.exe -deprecation switch. Then look in the Javadoc for the deprecated methods to find out the recommended replacements. Sometimes you just have to rename. Sometimes the replacements work quite differently. But I'm not really understand how it works, can anybody help me with this?

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  • Design a mini script language

    - by radi
    hi , my project this year is to develop a text mining tool (with new features) so we need a mini script language in this tool to add annotation to texts this language should be simple and like lisp grammars (left and right side) . what i need is how to design this language ,i know how to constract the compiler , but how to write language grammars ? , and i want to use some mini open source language or any language bnf please advice me and if there is a language i can use and customize to meet my needs ? thanks

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  • Control is set to false, jQuery selector fails

    - by Damien Joe
    Hi I have some controls on an asp.net modal which I show manually via code behind. Now I am trying to attach a selector on one of the controls inside pageLoad(), problem being is that the modal container is initially set to visible=false. I tried checking for length but it still throws exception if ($('#<%= myControl.ClientId %>').length > 0) { $('#<%= myControl.ClientID %>').click(function() { // Do work }); } Compiler Error Message: CS0103: The name 'myControl' does not exist in the current context

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  • How to compile a Windows binary in Ubuntu?

    - by George Edison
    I have a Qt application that I can compile in Ubuntu 10.04 64-bit and on Windows. However, I would like to avoid switching to Windows every time I want to compile the Windows version. Is there a way I can compile a Windows Qt executable in Ubuntu with mingw32 or something? Further, is there a way to integrate that compiler into Qt Creator?

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  • Declare a Dictionary inside a static class

    - by Ngu Soon Hui
    How to declare a static dictionary object inside a static class? I tried public static class ErrorCode { public const IDictionary<string , string > ErrorCodeDic =new Dictionary<string, string>() { {"1","User name or password problem"} }; } But the compiler complains that "A const field of a reference type other than string can only be initialized with null".

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  • Is it OK to put a standard, pure C header #include directive inside a namespace?

    - by mic_e
    I've got a project with a class log in the global namespace (::log). So, naturally, after #include <cmath>, the compiler gives an error message each time I try to instantiate an object of my log class, because <cmath> pollutes the global namespace with lots of three-letter methods, one of them being the logarithm function log(). So there are three possible solutions, each having their unique ugly side-effects. Move the log class to it's own namespace and always access it with it's fully qualified name. I really want to avoid this because the logger should be as convenient as possible to use. Write a mathwrapper.cpp file which is the only file in the project that includes <cmath>, and makes all the required <cmath> functions available through wrappers in a namespace math. I don't want to use this approach because I have to write a wrapper for every single required math function, and it would add additional call penalty (cancelled out partially by the -flto compiler flag) The solution I'm currently considering: Replace #include <cmath> by namespace math { #include "math.h" } and then calculating the logarithm function via math::log(). I have tried it out and it does, indeed, compile, link and run as expected. It does, however, have multiple downsides: It's (obviously) impossible to use <cmath>, because the <cmath> code accesses the functions by their fully qualified names, and it's deprecated to use in C++. I've got a really, really bad feeling about it, like I'm gonna get attacked and eaten alive by raptors. So my question is: Is there any recommendation/convention/etc that forbid putting include directives in namespaces? Could anything go wrong with diferent C standard library implementations (I use glibc), different compilers (I use g++ 4.7, -std=c++11), linking? Have you ever tried doing this? Are there any alternate ways to banish the math functions from the global namespace? I've found several similar questions on stackoverflow, but most were about including other C++ headers, which obviously is a bad idea, and those that weren't made contradictory statements about linking behaviour for C libraries. Also, would it be beneficial to additionally put the #include <math.h> inside extern "C" {}?

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