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  • Delegate Example From C# In Depth Confusion

    - by ChloeRadshaw
    I am looking at this example: List<Product> products = Product. GetSampleProducts() ; products.Sort( (first, second) => first.Name.CompareTo(second. Name) ) ; foreach (Product product in products) { Console. WriteLine(product) ; } What function is actually called in the API when you do that? Does the compiler create a class which implemnents the IComparer interface? I thought delegates were anonymous methods - Here it seems to be an anonymous interface implementation which is casuing confusion

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  • Why can't I project ToString() in VB?

    - by Martinho Fernandes
    If you try to compile the query below in Visual Basic .NET, it fails. From x In {1, 2} Select x.ToString() The error given by the compiler is: Range variable name cannot match the name of a member of the 'Object' class. There is nothing wrong with the equivalent C# query, though: from x in new[]{1, 2} select x.ToString() This does not happen with the ToString overload that takes a format (it is a member of Int32, not Object). It does happen with other members of Object, as long as they don't take an argument: with GetType and GetHashCode it fails; with Equals(object) it compiles. Why is this restriction in place, and what alternatives can I use?

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  • C++ standard: dereferencing NULL pointer to get a reference?

    - by shoosh
    I'm wondering about what the C++ standard says about code like this: int* ptr = NULL; int& ref = *ptr; int* ptr2 = &ref; In practice the result is that ptr2 is NULL but I'm wondering, is this just an implementation detail or is this well defined in the standard? Under different circumstances a dereferencing of a NULL pointer should result in a crash but here I'm dereferencing it to get a reference which is implemented by the compiler as a pointer so there's really no actual dereferencing of NULL.

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  • Using an int as the numerical representation of a string in C#

    - by bluewall21
    I'm trying to use an integer as the numerical representation of a string, for example, storing "ABCD" as 0x41424344. However, when it comes to output, I've got to convert the integer back into 4 ASCII characters. Right now, I'm using bit shifts and masking, as follows: int value = 0x41424344; string s = new string ( new char [] { (char)(value >> 24), (char)(value >> 16 & 0xFF), (char)(value >> 8 & 0xFF), (char)(value & 0xFF) }); Is there a cleaner way to do this? I've tried various casts, but the compiler, as expected, complained about it.

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  • C++ rvalue temporaries in template

    - by aaa
    hello. Can you please explain me the difference between mechanism of the following: int function(); template<class T> void function2(T&); void main() { function2(function()); // compiler error, instantiated as int & const int& v = function(); function2(v); // okay, instantiated as const int& } is my reasoning correct with respect to instantiation? why is not first instantiated as const T&? Thank you

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  • Best environment to port C/C++ code from Linux to Windows.

    - by Simone Margaritelli
    I'd like to make a big project of mine buildable on Windows platforms. The project itself it's written in C/C++ following POSIX standards, with some library dependencies such as libxml2, libcurl and so on. I'm more a Linux developer rather than a Windows developer, so i have no idea of which compiler suite i should use to port the code. Which one offers more compatibility with gcc 4.4.3 i'm using right now? My project needs flex and bison, is there any "ready to use" environment to port such projects to windows platforms? Thanks.

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  • a macro question for c language (#define)

    - by Daniel
    I am reading source code of hoard memory allocator, and in the file of gnuwrapper.cpp, there are the following code #define CUSTOM_MALLOC(x) CUSTOM_PREFIX(malloc)(x) What's the meaning of CUSTOM_PREFIX(malloc)(x)? is CUSTOM_PREFIX a function? But as a function it didn't defined anywhere. If it's variable, then how can we use variable like var(malloc)(x)? more code: #ifndef __GNUC__ #error "This file requires the GNU compiler." #endif #include <string.h> #include <stdlib.h> #include <stdio.h> #include <malloc.h> #ifndef CUSTOM_PREFIX ==> here looks like it's a variable, so if it doesn't define, then define here. #define CUSTOM_PREFIX #endif #define CUSTOM_MALLOC(x) CUSTOM_PREFIX(malloc)(x) ===> what's the meaning of this? #define CUSTOM_FREE(x) CUSTOM_PREFIX(free)(x) #define CUSTOM_REALLOC(x,y) CUSTOM_PREFIX(realloc)(x,y) #define CUSTOM_MEMALIGN(x,y) CUSTOM_PREFIX(memalign)(x,y)

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  • How to strip debug code during compile time in C++?

    - by juvenis
    Say I have a C++ function debugPrint(int foo). How can I most conveniently strip that from release builds? I do not want to surround every call to debugPrint with #ifdefs as it would be really time consuming. On the other hand, I want to be 100% sure that the compiler strips all the calls to that function, and the function itself from release builds. The stripping should happen also, if it's called with a parameter that results from a function call. E.g., debugPrint(getFoo());. In that case I want also the getFoo() call to be stripped. I understand that function inlining could be an option, but inlining is not guaranteed to be supported.

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  • [VB.NET] Same name methods in different modules cause ambiguity.

    - by smwikipedia
    I have 2 modules. Each contains a Sub with the same name. See below: Module moduleA Public Sub f(ByVal arg1 As myType) Console.WriteLine("module A") End Sub End Module Module moduleB Public Sub f(ByVal arg1 As myType, ByVal arg2 As Boolean) Console.WriteLine("module B") End Sub End Module But the compiler complains that there's ambiguity between moduleA and moduleB. How could this be? I have totally different signatures. However, if I put the 2 methods into the same module, there's no ambiguity at all. Could someone tell me why? Many thanks.

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  • How to explain to a developer that adding extra if - else if conditions is not a good way to "improv

    - by Lilit
    Recently I've bumped into the following C++ code: if (a) { f(); } else if (b) { f(); } else if (c) { f(); } Where a, b and c are all different conditions, and they are not very short. I tried to change the code to: if (a || b || c) { f(); } But the author opposed saying that my change will decrease readability of the code. I had two arguments: 1) You should not increase readability by replacing one branching statement with three (though I really doubt that it's possible to make code more readable by using else if instead of ||). 2) It's not the fastest code, and no compiler will optimize this. But my arguments did not convince him. What would you tell a programmer writing such a code? Do you think complex condition is an excuse for using else if instead of OR?

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  • Why does a non-constant offsetof expression work?

    - by Chris J. Kiick
    Why does this work: #include <sys/types.h> #include <stdio.h> #include <stddef.h> typedef struct x { int a; int b[128]; } x_t; int function(int i) { size_t a; a = offsetof(x_t, b[i]); return a; } int main(int argc, char **argv) { printf("%d\n", function(atoi(argv[1]))); } If I remember the definition of offsetof correctly, it's a compile time construct. Using 'i' as the array index results in a non-constant expression. I don't understand how the compiler can evaluate the expression at compile time. Why isn't this flagged as an error?

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  • Why Does try ... catch Blocks Require Braces?

    - by Bidou
    Hello. While in other statements like if ... else you can avoid braces if there is only one instruction in a block, you cannot do that with try ... catch blocks: the compiler doesn't buy it. For instance: try do_something_risky(); catch (...) std::cerr << "Blast!" << std::endl; With the code above, g++ simply says it expects a '{' before do_something_risky(). Why this difference of behavior between try ... catch and, say, if ... else ? Thanks!

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  • Pattern matching against Scala Map type

    - by Tom Morris
    Imagine I have a Map[String, String] in Scala. I want to match against the full set of key–value pairings in the map. Something like this ought to be possible val record = Map("amenity" -> "restaurant", "cuisine" -> "chinese", "name" -> "Golden Palace") record match { case Map("amenity" -> "restaurant", "cuisine" -> "chinese") => "a Chinese restaurant" case Map("amenity" -> "restaurant", "cuisine" -> "italian") => "an Italian restaurant" case Map("amenity" -> "restaurant") => "some other restaurant" case _ => "something else entirely" } The compiler complains thulsy: error: value Map is not a case class constructor, nor does it have an unapply/unapplySeq method What currently is the best way to pattern match for key–value combinations in a Map?

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  • hook to save action in eclipse plugin

    - by 4485670
    I want to create a Google Closure Compiler plugin for eclipse. I already have a popup menu entry to compile a Javascript file to its minified version. But it would be more than helpful if every time you save a *.js that minified version would be generated automatically. I read/heard about natures and builders, extension points and IResourceChangeListener. But I did not manage to figure out what I should use and especially how to get it to work. Is there a working example of a plugin that does "the same kind of thing" so I can work from that or a tutorial to write such? With the answer below I searched for projects that use the IResourceChangeListener and came up with this code: manifest: http://codepaste.net/3yahwe plugin.xml: http://codepaste.net/qek3rw activator: http://codepaste.net/s7xowm DummyStartup: http://codepaste.net/rkub82 MinifiedJavascriptUpdater: http://codepaste.net/koweuh There in the MinifiedJavascriptUpdater.java which holds the code for the IResourceChangeListener the "resourceChanged" function is never reached.

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  • Is new int[10]() valid c++?

    - by Naveen
    While trying to answer this question I found that the code int* p = new int[10](); compiles fine with VC9 compiler and initializes the integers to 0. So my questions are: First of all is this valid C++ or is it a microsoft extension? Is it guaranteed to initialize all the elements of the array? Also, is there any difference if I do new int; or new int();? Does the latter guarantee to initialize the variable?

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  • Problem with non-copyable classes

    - by DeadMG
    I've got some non-copyable classes. I don't invoke any of the copy operators or constructor, and this code compiles fine. But then I upgraded to Visual Studio 2010 Ultimate instead of Professional. Now the compiler is calling the copy constructor- even when the move constructor should be invoked. For example, in the following snippet: inline D3D9Mesh CreateSphere(D3D9Render& render, float radius, float slices) { D3D9Mesh retval(render); /* ... */ return std::move(retval); } Error: Cannot create copy constructor, because the class is non-copyable. However, I quite explicitly moved it.

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  • Typecasting doesn't work. How to convert an object?

    - by Nastase Ion
    Hi everyone! I need to convert a custom object to a different object. How can I do that? I know that typecasting doesn't work (the only thing is does is "shuts the compiler warnings off", but nothing more). Here is a sample code: MyType* obj1; MyOtherType* obj2; obj1 = [MyType initWithData: 1]; obj2 = (MyOtherType*) obj1; if ([obj2 isMemberOfClass: [MyOtherType class]]) { NSLog(@"OK"); } else if ([obj2 isMemberOfClass: [MyType class]]) { NSLog(@"Nope"); } The result is: Nope What can I do??

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  • XCode Project Code Changes Not Updating 100% After Save-Build-Run

    - by Greg
    When I make code changes to my iPhone game project in XCode, and then do CMD-B + Enter, I expect the project to be saved, build and run on the simulator with the latest. What is happening though, sometimes, is that it doesn't pick up a small change I make unless I clean the project and then build. I'm a long time Java person and newish to C-based languages and it's compiler. Can someone explain to me what is cached after each build that does this and how to change my project settings to avoid having to clean everytime? Or tell me the bad news that this is part of C development? Not trying to bash it - I get compiled JSPs stuck in the working cache often in Java, too. :P

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  • Why Do try ... catch Blocks Require Braces?

    - by Bidou
    Hello. While in other statements like if ... else you can avoid braces if there is only one instruction in a block, you cannot do that with try ... catch blocks: the compiler doesn't buy it. For instance: try do_something_risky(); catch (...) std::cerr << "Blast!" << std::endl; With the code above, g++ simply says it expects a '{' before do_something_risky(). Why this difference of behavior between try ... catch and, say, if ... else ? Thanks!

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  • I want to make a wrapped acces type for certain internals of one of classes and I have some performa

    - by Alex
    I am writing an abstract matrix class (and some concrete subclasses) for use on very differing hardwares/architectures, etc. and I want to write a row and column type that provides a transparent reference to the rows and columns of the matrix. However, I want to tune for performance, so I'd like this class to be essentially a compiler construct. In other words, I'm willing to sacrifice some dev time to making the overhead of these classes as small as possible. I assume all (small) methods would want to be virtual? Keep the structure small? Any other suggestions?

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  • Strange macro declaration in C

    - by Andrey Atapin
    Exploring libusb-1.0.9 source code, I have found such line (./os/poll_windows.c:78): #define CHECK_INIT_POLLING do {if(!is_polling_set) init_polling();} while(0) As for me this is the same like: #define CHECK_INIT_POLLING if(!is_polling_set) init_polling(); Is there any reason to loop that expression? UPDATE: I couldn't still realize what'd be wrong after the answers, and the following example helped: #include <stdio.h> #define TEST if(test) foo(); #define TEST_DO do { if(test) foo(); } while(0) int test = 1; void foo() { printf("%s", "Foo called"); } int main(int argc, char** argv) { if(argc > 1) TEST_DO; /* LINE 12 */ else printf("%s", "skipping..."); return 0; } If you put TEST at line 12, a compiler will give an error "error: ‘else’ without a previous ‘if’". Hope, this will help someone.

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  • Should I use C(99) booleans ? ( also c++ booleans in c++ ?)

    - by Roman A. Taycher
    I haven't done much c programming but when I do when I need a false I put 0 when I want true I put 1, (ex. while(1)), in other cases I use things like "while(ptr)" or "if(x)". Should I try using C99 booleans, should I recommend them to others if I'm helping people new to programming learn c basics(thinking of cs 1?? students)? I'm pretty sure the Visual Studio compiler supports c99 bools, but do a lot of projects (open source and c apps in industry) compile for c89? If I don't use C bools should I at least do something like #define TRUE 1 #define FALSE 0? Also what about c++ Booleans (for c++)?

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  • int vs const int&

    - by Valdo
    I've noticed that I usually use constant references as return values or arguments. I think the reason is that it works almost the same as using non-reference in the code. But it definitely takes more space and function declarations become longer. I'm OK with such code but I think some people my find it a bad programming style. What do you think? Is it worth writing const int& over int? I think it's optimized by the compiler anyway, so maybe I'm just wasting my time coding it, a?

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  • What's the outcome if I use free with new or delete with malloc?

    - by skydoor
    It is a compiler error or runtime error? The code below can be compiled! class Base{ void g(); void h(); }; int main() { Base* p = new Base(); free(p); return 0; } However it can't be compiled with a virtual function if I declare the class Base like this class Base{ virtual void g(); void h(); }; The code below can be compiled all the time, no matter the function is virtual or not. class Base{ void g(); void h(); }; int main() { Base* p = (Base*)malloc(sizeof(Base)); delete p; return 0; }

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  • Isses using function with variadic arguments

    - by Sausages
    I'm trying to write a logging function and have tried several different attempts at dealing with the variadic arguments, but am having problems with all of them. Here's the latest: - (void) log:(NSString *)format, ... { if (self.loggingEnabled) { va_list vl; va_start(vl, format); NSString* str = [[NSString alloc] initWithFormat:format arguments:vl]; va_end(vl); NSLog(format); } } If I call this like this: [self log:@"I like: %@", @"sausages"]; Then I get an EXC_BAD_ACCESS at the NSLog line (there's also a compiler warning that the format string is not a string literal). However if in XCode's console I do "po str" it displays "I like: sausages" so str seems ok.

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