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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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  • Can't get GetModuleFileNameA to work, keep getting error 'missing type specifier...'

    - by flavour404
    Hi, I am trying to use 'GetModuleFileNameA' but I keep getting the error 'c4430: missing type specifier - int assumed'. From reading the results from my google search I am guessing that it is from my use of NULL: char Filename[MAX_PATH]; //this is a char buffer GetModuleFileNameA(NULL, Filename, sizeof(Filename)); NULL is supposedly defined in #include stdio.h which I have included in my project, what am I doing wrong? Thanks.

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  • How to add the document library column named "Type (icon linked to document)" into list view?

    - by Sushant
    I am working with a list view. I want a column to have look similar to the document library column named "Type (icon linked to document)" column. I should also be able to set the path this hyperlinked icon should open. I tried a lot with existing site columns but could still not figure out how to do this. Has anyone implemented this earlier. Please share your expertise. Thanks in advance.

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  • Problem with C function of type char pointer, can someone explain?

    - by JJ
    Find the errors from following C function : char* f(int i) { int i; char buffer[20]; switch ( i ) { 1: strcpy( buffer, "string1"); 2: strcpy( buffer, "string2"); 3: strcpy( buffer, "string3"); default: strcpy(buffer, "defaultstring"); } return buffer; } this is c funtion not C++, I think it has to do with type conversion my compiler give warning that declaration of int i shadows a parameter.

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  • How to make OSX application that just runs opens some file type and runs arbitrary Ruby code?

    - by taw
    It's trivial to make a program executable from shell - just put #!/usr/bin/ruby on top, chmod +x it and done. Unfortunately OSX won't let me associate file type with such scripts - it requires its .apps instead. This sort of distinction doesn't seem to exist on other operating systems. What's the simplest way of making such .app, which would merely execute some arbitrary Ruby code?

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  • HTML / CSS How to add image icon to input type="button" ?

    - by Brett
    Hi, I'm using this css, but it puts an image in the center. Any way to left or right align an icon using an input type="button" html button, so that the text and the image fit on the button nicely? background: url('/common/assets/images/icons/16x16/add.png');background-position:center;background-repeat:no-repeat;

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  • How to display full documentation of a method as you type in VS?

    - by drasto
    The title is pretty descriptive... Is there any extension that let me see FULL documentation of the method I'm typing ? I would like to see the documentation as I can see it in Object Browser with description of parameters and everything not just some "summary". So what I'd like to see when I type String.Format is: Of cause with an option to see all overrides. It may be part of intelisence or I don't know what it does not really matter.

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  • How to find the class object of Java generic type?

    - by Samuel Yung
    Assume I have a generic type P which is an Enum, that is <P extends Enum<P>>, and I want to get the Enum value from a string, for example: String foo = "foo"; P fooEnum = Enum.valueOf(P.class, foo); This will get a compile error because P.class is invalid. So what can I do in order to make the above code work?

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  • How to create 2D jagged array

    - by Ram
    In my code an array is declared as follows private Object[,] cellInfos = new Object[20, 10]; I need to convert it into Jagged array so I wrote following code private Object[][] cellInfos = { new Object[20], new Object[10] }; But it gave me a array with 2 items each of type array. I need to create 2D array where new Object[20] would be first column and new Object[10] would be the second one. Thanks.

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