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  • Can an html element have multiple ids?

    - by webmat
    I understand that an id must be unique within an HTML/XHTML page. My question is, for a given element, can I assign multiple ids to it? <div id="nested_element_123 task_123"></div> I realize I have an easy solution with simply using a class. I'm just curious about using ids in this manner.

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  • Scope of the c++ using directive

    - by ThomasMcLeod
    From section 7.3.4.2 of the c++11 standard: A using-directive specifies that the names in the nominated namespace can be used in the scope in which the using-directive appears after the using-directive. During unqualified name lookup (3.4.1), the names appear as if they were declared in the nearest enclosing namespace which contains both the using-directive and the nominated namespace. [ Note: In this context, “contains” means “contains directly or indirectly”. —end note ] What do the second and third sentences mean exactly? Please give example. Here is the code I am attempting to understand: namespace A { int i = 7; } namespace B { using namespace A; int i = i + 11; } int main(int argc, char * argv[]) { std::cout << A::i << " " << B::i << std::endl; return 0; } It print "7 7" and not "7 18" as I would expect. Sorry for the typo, the program actually prints "7 11".

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  • Number of characters recommended for a statement

    - by liaK
    Hi, I have been using Qt 4.5 and so do C++. I have been told that it's a standard practice to maintain the length of each statement in the application to 80 characters. Even in Qt creator we can make a right border visible so that we can know whether we are crossing the 80 characters limit. But my question is, Is it really a standard being followed? Because in my application, I use indenting and all, so it's quite common that I cross the boundary. Other cases include, there might be a error statement which will be a bit explanatory one and which is in an inner block of code, so it too will cross the boundary. Usually my variable names look bit lengthier so as to make the names meaningful. When I call the functions of the variable names, again I will cross. Function names will not be in fewer characters either. I agree a horizontal scroll bar shows up and it's quite annoying to move back and forth. So, for function calls including multiple arguments, when the boundary is reached I will make the forth coming arguments in the new line. But besides that, for a single statement (for e.g a very long error message which is in double quotes " " or like longfun1()->longfun2()->...) if I use an \ and split into multiple lines, the readability becomes very poor. So is it a good practice to have those statement length restrictions? If this restriction in statement has to be followed? I don't think it depends on a specific language anyway. I added C++ and Qt tags since if it might. Any pointers regarding this are welcome.

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  • Why does C++ allow variable length arrays that aren't dynamically allocated?

    - by Maulrus
    I'm relatively new to C++, and from the beginning it's been drilled into me that you can't do something like int x; cin >> x; int array[x]; Instead, you must use dynamic memory. However, I recently discovered that the above will compile (though I get a -pedantic warning saying it's forbidden by ISO C++). I know that it's obviously a bad idea to do it if it's not allowed by the standard, but I previously didn't even know this was possible. My question is, why does g++ allow variable length arrays that aren't dynamically allocated if it's not allowed by the standard? Also, if it's possible for the compiler to do it, why isn't it in the standard?

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  • In C++, what happens when you return a variable?

    - by wowus
    What happens, step by step, when a variable is returned. I know that if it's a built-in and fits, it's thrown into rax/eax/ax. What happens when it doesn't fit, and/or isn't built-in? More importantly, is there a guaranteed copy constructor call? edit: What about the destructor? Is that called "sometimes", "always", or "never"?

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  • Is or Are to prefix boolean values

    - by Brian T
    When naming a boolean, or a function returning a boolean it's usual to prefix with 'is' e.g. isPointerNull isShapeSquare What about when refering to multiple items, should it be: arePointersNull or isPointersNull areShapesNull or isShapesNull I can see arguments for both; is offers consistency and perhaps slightly better readability, are makes the code read in a more natural way. Any opinions?

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  • Console Application Structure

    - by Paul Fox
    I've written several .Net Console Applications over the past 6 months and we have many more throughout different projects in our organization. I generally stick to the same standard format/structure for my Console Applications. Unfortunately, many of our console applications do not. I have been looking into ways of standardizing the structure of these Console Applications. I would also like to provide a framework for the basic structure of a Console Application and provide easy access to standard ways of handling things such as argument passing, logging, etc. Can anyone suggest Best Practices for addressing these concerns? I have been reading this MSDN article on Console Applications in .Net which suggests a Design Pattern for Console Apps. The example uses a Template Method pattern to handle some of the concerns I listed earlier. Two negatives of using this approach are listed in the article. Ending up with twice as many classes Having many simple, similar classes Can anyone suggest better, or more standard, ways of handling this? What about listing additional negatives with this approach?

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  • Is there any pros to duplicate browser/keyboard functionality?

    - by metal-gear-solid
    Is it good for user experience to duplicate browser/keyboard functionality? For example: to provide these links on a web-page. "Back to top" link "Print this page" link "Add to Favorite" link "Back" button/link "Text zoom" button Are they really create Site's usability and accessibility? How screen reader will behave these links, will these confuse to screen reader users?

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  • Template access of symbol in unnamed namespace

    - by Fred Larson
    We are upgrading our XL C/C++ compiler from V8.0 to V10.1 and found some code that is now giving us an error, even though it compiled under V8.0. Here's a minimal example: test.h: #include <iostream> #include <string> template <class T> void f() { std::cout << TEST << std::endl; } test.cpp: #include <string> #include "test.h" namespace { std::string TEST = "test"; } int main() { f<int>(); return 0; } Under V10.1, we get the following error: "test.h", line 7.16: 1540-0274 (S) The name lookup for "TEST" did not find a declaration. "test.cpp", line 6.15: 1540-1303 (I) "std::string TEST" is not visible. "test.h", line 5.6: 1540-0700 (I) The previous message was produced while processing "f<int>()". "test.cpp", line 11.3: 1540-0700 (I) The previous message was produced while processing "main()". We found a similar difference between g++ 3.3.2 and 4.3.2. I also found in g++, if I move the #include "test.h" to be after the unnamed namespace declaration, the compile error goes away. So here's my question: what does the Standard say about this? When a template is instantiated, is that instance considered to be declared at the point where the template itself was declared, or is the standard not that clear on this point? I did some looking though the n2461.pdf draft, but didn't really come up with anything definitive.

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  • Does (size_t)((char *)0) ever not evaluate to 0?

    - by Bruce Christensen
    According to the responses in "Why subtract null pointer in offsetof()?" (and my reading of K&R), the C standard doesn't require that (size_t)((char *)0) == 0. Still, I've never seen a situation where casting a null pointer to an integer type evaluates to anything else. If there is a compiler or scenario where (size_t)((char *)0) != 0, what is it?

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  • What are the default style property values in HTML?

    - by Emanuil
    Most HTML elements have style properties associated with them - such a "color", "font-size" and "padding". These style properties have default values. For example the "color" style property associated with the "a" (anchor) element seems to have a default value of "#000066". What are the default style properties values fo in HTML?

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  • Using the standard OBJECT tag, how can I display a java applet with automatic prompts to install Java and with fallback content?

    - by CB
    This is the code i'm currently using: (note - %s is replaced on the server side) <!--[if !IE]>--> <object type="application/x-java-applet" width="300" height="300" > <!--<![endif]--> <!--[if IE]> <object classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" codebase="http://java.sun.com/update/1.6.0/jinstall-6u22-windows-i586.cab" type="application/x-java-applet" width="300" height="300" > <!--><!-- <![endif]--> <param name="codebase" value="/media/vnc/" > <param name="archive" value="TightVncViewer.jar" /> <param name="code" value="com.tightvnc.vncviewer.VncViewer" /> <param name="port" value="%s" /> <param name="Open New Window" value="yes" /> </object> When Java is installed, this works perfectly in both IE and Firefox. When Java is not installed, IE and Firefox both correctly prompt for an autodownload of Java 1.6 from the codebase line. (IE via the activex url given firefox via the Plugin Finder Service) Now, suppose I want fallback content to be shown if the plugin isn't installed, say a simple message like "Get Java". From reading the specs, i'd assume this should not change the plugin finding prompt - that is, rendering the fallback should be seen as a failure to render the object tag. Thus, I should still get the plugin finder service prompting me to install Java. Instead, simply adding a single character to the innerHTML of the object element causes Firefox to no longer prompt. Test this by visiting data:text/html,<object type='application/x-java-applet'>Java failed to load</object>. How can I keep firefox prompting to install Java while providing fallback content? URL to test Firefox's Java Plugin Finder Service: data:text/html,<object type='application/x-java-applet'/>

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  • If I don't odr-use a variable, can I have multiple definitions of it across translation units?

    - by sftrabbit
    The standard seems to imply that there is no restriction on the number of definitions of a variable if it is not odr-used (§3.2/3): Every program shall contain exactly one definition of every non-inline function or variable that is odr-used in that program; no diagnostic required. It does say that any variable can't be defined multiple times within a translation unit (§3.2/1): No translation unit shall contain more than one definition of any variable, function, class type, enumeration type, or template. But I can't find a restriction for non-odr-used variables across the entire program. So why can't I compile something like the following: // other.cpp int x; // main.cpp int x; int main() {} Compiling and linking these files with g++ 4.6.3, I get a linker error for multiple definition of 'x'. To be honest, I expect this, but since x is not odr-used anywhere (as far as I can tell), I can't see how the standard restricts this. Or is it undefined behaviour?

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  • Why use C typedefs rather than #defines?

    - by me_and
    What advantage (if any) is there to using typedef in place of #define in C code? As an example, is there any advantage to using typedef unsigned char UBYTE over #define UBYTE unsigned char when both can be used as void func() { UBYTE byte_value = 0; /* Do some stuff */ return byte_value; } Obviously the pre-processor will try to expand a #define wherever it sees one, which wouldn't happen with a typedef, but that doesn't seem to me to be any particular advantage or disadvantage; I can't think of a situation where either use wouldn't result in a build error if there was a problem.

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