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• How to call C++ function from C?

  - by claws

  I know this. Calling C function from C++: If my application was in C++ and I had to call functions from a library written in C. Then I would have used //main.cpp extern "C" void C_library_function(int x, int y);//prototype C_library_function(2,4);// directly using it. This wouldn't mangle the name C_library_function and linker would find the same name in its input *.lib files and problem is solved. Calling C++ function from C??? But here I'm extending a large application which is written in C and I need to use a library which is written in C++. Name mangling of C++ is causing trouble here. Linker is complaining about the unresolved symbols. Well I cannot use C++ compiler over my C project because thats breaking lot of other stuff. What is the way out? By the way I'm using MSVC

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• How do you keep Cocoa controllers from getting too big?

  - by zoul

  Hello! Do you have some tricks or techniques to break Cocoa controller classes into smaller chunks? I find that whatever I do the controllers end up being one of the more complicated classes in my design. The basic stuff is simple, but once I have several pop-overs or action sheets running, things get uncomfortably complex. It's not that bad, but still I would like to refactor the code into several standalone chunks. I thought about categories, but the code is not that independent (a lot of times it needs to tap into viewWillAppear, for example) and I find that I spend a long time fighting the compiler. I also thought about adding functionality in layers using inheritance, but that feels like a hack.

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• boost variant static_visitor problem picking correct function

  - by Steve

  I'm sure I'm having a problem with template resolution here, but I'm not sure why I'm having the problem. I have a static visitor I'm passing to boost variant where i've had to do template specialization for certain cases. The case for everything except for MyClass should throw in the static_visitor below. Unfortunately, when the visitor is applied to pull a MyClass out, it selects the most generic case rather than the exact match. I would type each case explicitly, but that will be rather long. So, why is the compiler resolving the most generic case over the exact match, and is there anyway to fix it template<> class CastVisitor<MyClass>:public boost::static_visitor<MyClass> { public: template<typename U> MyClass operator()(const U & i) const { throw std::exception("Unable to cast"); } MyClass operator()(const MyClass& i) { return i; } };

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• How would one call std::forward on all arguments in a variadic function?

  - by Noah Roberts

  I was just writing a generic object factory and using the boost preprocessor meta-library to make a variadic template (using 2010 and it doesn't support them). My function uses rval references and std::forward to do perfect forwarding and it got me thinking...when C++0X comes out and I had a standard compiler I would do this with real variadic templates. How though, would I call std::forward on the arguments? template < typename ... Params void f(Params ... params) // how do I say these are rvalue reference? { y(std::forward(...params)); //? - I doubt this would work. } Only way I can think of would require manual unpacking of ...params and I'm not quite there yet either. Is there a quicker syntax that would work?

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• Why does C++ linking use virtually no CPU? (updated)

  - by John

  On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no? update: so the obvious follow-up is, can VC++ compiler and linker talk together better to streamline things and keep OBJ files in memory, similar to how Delphi does?

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• How to know record has been updated successfully in php

  - by Lisa Ray

  $sql = "UPDATE...."; if(mysql_query($sql)) { $_SESSION['Trans']="COMMIT"; header("location:result.php"); exit; } else { $_SESSION['Trans']="FAIL"; $_SESSION['errors'] = "Error: Sorry! We are unable to update your Profile, Please contact to PNP HelpDesk."; header("location:result.php"); exit; }//end IF data is getting updated then why compiler is not coming inside IF condition.

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• Whats the difference between a C++ and a Cocoa Project in Xcode?

  - by david

  I need to work with TagLib for my project. I've created a framework (and I tried using it as a lib) but the compiler cannot find #include < strings on compiling (No such file or Directory). I've created a test C++ project and it #includes < strings just fine. I've looked at the project settings and I cannot find a difference between them. But the standard cocoa projects obviously so not have the search path set to include C++ libraries (Or am I completely getting it wrong?). I've searched for a solution but no one else seems to have run into this problem.

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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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• Visual Studio 2010 Compiling C code

  - by Corsen2000

  I have the following code snippet. This is a c file in visual studio 2010. If i try to compile this with the line: int hello = 10; commented out it will compile just fine. If I comment that line in it will not compile. Am I missing something or should I not be using Visual Studio 2010 to compile C code. If this is a Visual Studio problem can anyone recommend a easy to use IDE / Compiler that I can for C. Thank You int* x = (int*) calloc(1, sizeof(int)); *x = 5; //int hello = 10; printf("Hello World! %i", *x); getchar();

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• Operator as and generic classes

  - by abatishchev

  I'm writing .NET On-the-Fly compiler for CLR scripting and want execution method make generic acceptable: object Execute() { return type.InvokeMember(..); } T Execute<T>() { return Execute() as T; /* doesn't work: The type parameter 'T' cannot be used with the 'as' operator because it does not have a class type constraint nor a 'class' constraint */ // also neither typeof(T) not T.GetType(), so on are possible return (T) Execute(); // ok } But I think operator as will be very useful: if result type isn't T method will return null, instead of an exception! Is it possible to do?

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• Pass an event into a constructor

  - by Vaccano

  I have a class that I want to be able the handle the mouse up event for a grid. I tried to create it with a static method call like this: MyDataBinding.BindObjectsToDataGrid(ListOfObjectsToBind, myGrid.MouseUp); The end goal being that in the method I would assign a delegate to the MouseUp PassedInMouseUp += myMethodThatWillHandleTheMouseUp; Looks good here (to me) but the compiler chokes on the first line. It says that I can only use MouseUp with a += or a -=. Clearly I am going about this the wrong way. How can I get a different class to handle the mouse up with out having to: Pass in the whole grid Expose the method that will be handling the mouse up as a public method. Or, is this just a limitation and I will have to do one of the above?

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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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• Are C++ Templates just Macros in disguise?

  - by Roddy

  I've been programming in C++ for a few years, and I've used STL quite a bit and have created my own template classes a few times to see how it's done. Now I'm trying to integrate templates deeper into my OO design, and a nagging thought keeps coming back to me: They're just a macros, really... You could implement (rather UGLY) auto_ptrs using #defines, if you really wanted to. This way of thinking about templates helps me understand how my code will actually work, but I feel that I must be missing the point somehow. Macros are meant evil incarnate, yet "template metaprogramming" is all the rage. So, what ARE the real distinctions? and how can templates avoid the dangers that #define leads you into, like Inscrutable compiler errors in places where you don't expect them? Code bloat? Difficulty in tracing code? Setting Debugger Breakpoints?

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• Cast vector<T> to vector<const T>

  - by user345386

  I have a member variable of type vector (where is T is a custom class, but it could be int as well.) I have a function from which I want to return a pointer to this vector, but I don't want the caller to be able to change the vector or it's items. So I want the return type to be const vector* None of the casting methods I tried worked. The compiler keeps complaining that T is not compatible with const T. Here's some code that demonstrates the gist of what I'm trying to do; vector<int> a; const vector<const int>* b = (const vector<const int>* ) (&a); This code doesn't compile for me. Thanks in advance!

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• Java generic Interface performance

  - by halfwarp

  Simple question, but tricky answer I guess. Does using Generic Interfaces hurts performance? Example: public interface Stuff<T> { void hello(T var); } vs public interface Stuff { void hello(Integer var); <---- Integer used just as an example } My first thought is that it doesn't. Generics are just part of the language and the compiler will optimize it as though there were no generics (at least in this particular case of generic interfaces). Is this correct?

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• Operators vs Functions in C/C++

  - by user356106

  Someone recently asked me the difference between a C++ standard operator (e.g. new,delete,sizeof) and function (e.g. tan,delete, malloc). By "standard" I mean those provided by default by the compiler suite, and not user defined. Below were the answers I gave, though neither seemed satisfactory. (1) An operator doesn't need any headers to be included to use it : E.g. you can have a call to new without including any headers. However, a function (say free() ) does need headers included, compulsorily. (2) An operator is defined as such (ie as a class operator) somewhere in the standard headers. A function isn't. Can you critique these answers and give me a better idea of the difference?

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• Best way to access nested data structures?

  - by Blackshark

  I would like to know what the best way (performance wise) to access a large data structure is. There are about hundred ways to do it but what is the most accessible for the compiler to optimize? One can access a value by foo[someindex].bar[indexlist[i].subelement[j]].baz[0] or create some pointer aliases like sometype_t* tmpfoo = &foo[someindex]; tmpfoo->bar[indexlist[i].subelement[j]].baz[0] or create reference aliases like sometype_t &tmpfoo = foo[someindex]; tmpfoo.bar[indexlist[i].subelement[j]].baz[0] and so forth...

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• Constant embedded for loop condition optimization in C++ with gcc

  - by solinent

  Will a compiler optimize tihs: bool someCondition = someVeryTimeConsumingTask(/* ... */); for (int i=0; i<HUGE_INNER_LOOP; ++i) { if (someCondition) doCondition(i); else bacon(i); } into: bool someCondition = someVeryTimeConsumingTask(/* ... */); if (someCondition) for (int i=0; i<HUGE_INNER_LOOP; ++i) doCondition(i); else for (int i=0; i<HUGE_INNER_LOOP; ++i) bacon(i); someCondition is trivially constant within the for loop. This may seem obvious and that I should do this myself, but if you have more than one condition then you are dealing with permuatations of for loops, so the code would get quite a bit longer. I am deciding on whether to do it (I am already optimizing) or whether it will be a waste of my time.

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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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• Why do I have to give an identifier?

  - by Knowing me knowing you

  In code: try { System.out.print(fromClient.readLine()); } catch(IOException )//LINE 1 { System.err.println("Error while trying to read from Client"); } In code line marked as LINE 1 compiler forces me to give an identifier even though I'm not using it. Why this unnatural constrain? And then if I type an identifier I'm getting warning that identifier isn't used. It just doesn't make sense to me, forcing a programmer to do something unnecesarry and surplus. And after me someone will revise this code and will be wondering if I didn't use this variable on purpouse or I just forgot. So in order to avoid that I have to write additional comment explaining why I do not use variable which is unnecessary in my code. Thanks

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• Class basic operators

  - by swan

  Hi, Is it necessary to have a copy constructor, destructor and operator= in a class that have only static data member, no pointer class myClass{ int dm; public: myClass(){ dm = 1; } ~myClass(){ } // Is this line usefull ? myClass(const myClass& myObj){ // and that operator? this->dm = myObj.dm; } myClass& operator=(const myClass& myObj){ // and that one? if(this != &myObj){ this->dm = myObj.dm; } return *this; } }; I read that the compiler build one for us, so it is better to not have one (when we add a data member we have to update the operators)

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• F# function calling syntax confusion

  - by Daniel

  I have a piece of code: links |> Seq.map (fun x -> x.GetAttributeValue ("href", "no url")) Which I wanted to rewrite to: links |> Seq.map (fun x -> (x.GetAttributeValue "href" "no url")) But the F# compiler doesn't seem to like that. I was under the impression that these two function calls were interchangeable: f (a, b) (f a b) The error that I get is: The member or object constructor 'GetAttributeValue' taking 2 arguments are not accessible from this code location. All accessible versions of method 'GetAttributeValue' take 2 arguments. Which seems amusing, as it seems to indicate that it needs what I'm giving it. What am I missing here?

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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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• Mysterious c debugging problem when trying to utilize printfs

  - by O_O

  Ok, folks. I've never encountered this before and it boggles the mind and is illogical. I have a somewhat complex loop and I want to try and see if everything is working by putting some printf statements. I look the intermediate products using printf and verify that the answer is ok. Then, when I comment out the printf to the intermediate products, the answer is WRONG. Has anyone ever encountered this? This is driving me insane and I don't see how the printfs could change an answer.... X_x If it helps, I am using a c/c++ compiler for a DSP. Thanks for any advice.. Here is a snippet... printf("splitBackground = %d, numWindowPoints = %d\n", splitBackground, numWindowPoints); splitBackground = splitBackground/numWindowPoints; printf("%d ", splitBackground); This is good but when I comment out the first line of code, it turns out to be hugely incorrect. :(

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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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