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  • How to reliably specialize template with intptr_t in 32 and 64 bit environments?

    - by vava
    I have a template I want to specialize with two int types, one of them plain old int and another one is intptr_t. On 64 bit platform they have different sizes and I can do that with ease but on 32 bit both types are the same and compiler throws an error about redefinition. What can I do to fix it except for disabling one of definitions off with preprocessor? Some code as an example: template<typename T> type * convert(); template<> type * convert<int>() { return getProperIntType(sizeof(int)); } template<> type * convert<intptr_t>() { return getProperIntType(sizeof(intptr_t)); } //this template can be specialized with non-integral types as well, // so I can't just use sizeof() as template parameter. template<> type * convert<void>() { return getProperVoidType(); }

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  • Strange difference between optimized/non optimized microsoft c++ code

    - by Anders Forsgren
    I have a c++ program with a method that looks something like this: int myMethod(int* arr1, int* arr2, int* index) { arr1--; arr2--; int val = arr1[*index]; int val2 = arr2[val]; doMoreThings(val); } With optimizations enabled (/O2) the first line where the first pointer is decremented is not executed. I assume the compiler believes that the arr1 array is not used since it thinks it can remove the decrement. Am I violating some convention in the above code? What could cause this behavior? It is a very old piece of f2c-translated code, the pointer decrement is due to the 1-based indexing of the original code.

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  • Linking Error: undefined reference to `MPI_Init' on Windows 7

    - by fatpipp
    I am using OpenMPI library to write a program to run on Windows 7. I compile and build with C Free 4.0, Mingw. Compiling is Ok but when the compiler links object, errors "undefined reference to ..." occurs. I have set the environment already: I added OpenMPI lib, include and bin folder into C Free Build Directories. I added them into Windows environment variables too. But the error still occurs. Can anyone tell me how to fix it? Thanks a lot.

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  • Dollar sign and/or Dash breaking Razor's parser

    - by justSteve
    the end-result i'm trying to render: <input type="radio" name="options" id="options_1" />$1 - A Not Very Expensive Chocolate <input type="radio" name="options" id="options_2" />$10 - A Kinda Expensive Chocolate <input type="radio" name="options" id="options_3" />$100 - A Really Expensive Chocolate From this code: @foreach (var o in Model.Options){ <input type="radio" name="options" id=@("options_" + @o.ID) />[email protected] - @o.Label } If i drop both the '$' and the '-' from what should be plain old text - stuff works. Adding either resulted in compiler warnings and runtime errors. I've tried the explicit syntax as described here but haven't found the right combination yet.

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  • doubt in Exceptions

    - by Ajay Singh
    class MyException extends Exception { MyException() {} MyException(String msg) { super(msg);} } public class NewException { static void f() throws MyException { System.out.println("throwing exception from f()"); throw new ClassCastException(); } static void g() throws MyException { System.out.println("throwing exception from g()"); throw new MyException("parametrized "); } public static void main(String ...strings ) { try { f(); } catch(MyException e) { e.printStackTrace(System.out); } try { g(); } catch(MyException e) { e.printStackTrace(System.out); } } } In the function f() iam specifying that "MyException " exception will be thrown and actually iam throwing some other exception which has no relation with MyException but still the compiler does not report any complain.Why is it so??

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  • C++ Translation Phase Confusion

    - by blakecl
    Can someone explain why the following doesn't work? int main() // Tried on several recent C++ '03 compilers. { #define FOO L const wchar_t* const foo = FOO"bar"; // Will error out with something like: "identifier 'L' is undefined." #undef FOO } I thought that preprocessing was done in an earlier translation phase than string literal operations and general token translation. Wouldn't the compiler be more or less seeing this: int main() { const wchar_t* const foo = L"bar"; } It would be great if someone could cite an explanation from the standard.

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  • Why is super.super.method(); not allowed in Java?

    - by Tim Büthe
    I read this question and thought that would easily be solved (not that it isn't solvable without) if one could write: @Override public String toString() { return super.super.toString(); } I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages. What do you guys think? EDIT: To clarify: yes I know, that's impossible to at to Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.

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  • Casting to specific asp.net page type

    - by DEH
    I have an asp.net page with a code-behind class definition as follows: public partial class examplepage : System.Web.UI.Page I'd like to set a public property within the page that I can reference from other classes. My understanding is that if I cast to examplepage then I should be able to get at the public property that is specific to example page, as in: string test=((examplepage)HttpContext.Current.Handler).propertyX; However, when I try casting as above the compiler does not recognise examplepage. Can anyone tell me how I can cast? I have no specific namespaces defined. Thanks

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  • Is it legal for a C++ reference to be NULL?

    - by BCS
    A while back I ran into a bug the looked something like this: void fn(int &i) { printf(&i == NULL ? "NULL\n" : "!NULL\n"); } int main() { int i; int *ip = NULL; fn(i); // prints !NULL fn(*ip); // prints NULL return 0; } More recently, I ran into this comment about C++ references: [References arguments make] it clear, unlike with pointers, that NULL is not a possible value. But, as show above, NULL is a possible value. So where is the error? In the language spec? (Unlikely.) Is the compiler in error for allowing that? Is that coding guide in error (or a little ambiguous)? Or am I just wandering into the minefield known as undefined behavior?

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  • Does C++ require a destructor call for each placement new?

    - by Josh Haberman
    I understand that placement new calls are usually matched with explicit calls to the destructor. My question is: if I have no need for a destructor (no code to put there, and no member variables that have destructors) can I safely skip the explicit destructor call? Here is my use case: I want to write C++ bindings for a C API. In the C API many objects are accessible only by pointer. Instead of creating a wrapper object that contains a single pointer (which is wasteful and semantically confusing). I want to use placement new to construct an object at the address of the C object. The C++ object will do nothing in its constructor or destructor, and its methods will do nothing but delegate to the C methods. The C++ object will contain no virtual methods. I have two parts to this question. Is there any reason why this idea will not work in practice on any production compiler? Does this technically violate the C++ language spec?

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  • C++ assignment - stylish or performance?

    - by joejax
    Having been writing Java code for many years, I was amazed when I see this C++ statement: int a,b; int c = (a=1, b=a+2, b*3); My question is: Is this a choice of coding style, or it has real benefit? (looking for a practicle use case) I think the compiler will see it the same as following: int a=1, b=a+2; int c = b*3; (What's the offical name for this? I assume it's a standard C/C++ syntax.)

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  • C++0x implementation guesstimates?

    - by dsimcha
    The C++0x standard is on its way to being complete. Until now, I've dabbled in C++, but avoided learning it thoroughly because it seems like it's missing a lot of modern features that I've been spoiled by in other languages. However, I'd be very interested in C++0x, which addresses a lot of my complaints. Any guesstimates, after the standard is ratified, as to how long it will take for major compiler vendors to provide reasonably complete, production-quality implementations? Will it happen soon enough to reverse the decline in C++'s popularity, or is it too little, too late? Do you believe that C++0x will become "the C++" within a few years, or do you believe that most people will stick to the earlier standard in practice and C++0x will be somewhat of a bastard stepchild, kind of like C99?

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  • Why can I derived from a templated/generic class based on that type in C# / C++

    - by stusmith
    Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

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  • How to use #ifdef entities as part of functions in header files

    - by Crazyjavahacking
    I would like to ask if it is possible to use the entities defined in #ifdef block in header files. To be clear, I have following code: #ifdef #include <winsock2.h> #define SOCKET_HANDLE SOCKET #define CONNECTION_HANDLE SOCKET #endif SOCKET_HANDLE createServerSocket(const char* hostAddress, short port); I am Java developer and this seems completely fine for me. However compiler has a problem with this. Can you explain why is that code a problem? Also how can I force to compile it. (The idea is to have generic interface and conditional compilation to determine real types according to running platform at compile time.) Thanks

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  • C Struct : typedef Doubt !

    - by Mahesh
    In the given code snippet, I expected the error symbol Record not found. But it compiled and ran fine on Visual Studio 2010 Compiler. I ran it as a C program from Visual Studio 2010 Command Prompt in the manner - cl Record.c Record Now the doubt is, doesn't typedef check for symbols ? Does it work more like a forward declaration ? #include "stdio.h" #include "conio.h" typedef struct Record R; struct Record { int a; }; int main() { R obj = {10}; getch(); return 0; }

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  • C++ template overloading - wrong function called

    - by DeadMG
    template<typename T> T* Push(T* ptr); template<typename T> T* Push(T& ref); template<typename T, typename T1> T* Push(T1&& ref); I have int i = 0; Push<int>(i); But the compiler calls it ambiguous. How is that ambiguous? The second function is clearly the preferred match since it's more specialized. Especially since the T1&& won't bind to an lvalue unless I explicitly forward/move it. Sorry - i is an int. Otherwise, the question would make no sense, and I thought people would infer it since it's normally the loop iterator.

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  • Array::ConvertAll in managed C++

    - by danny.lesnik
    This is a continuation from this post. I'm trying to parse this string in managed C++: String ^ rgba = "[0.09019608,0.5176471,0.9058824,1]"; cli::array<System::Double> ^ RGB = System::Array::ConvertAll<String,cli::array<System::Double> >((rgba->Substring(1,rgba->Length-2)->Split(',')),double::Parse); Compiler throws me the following error: Error 15 error C2770: invalid explicit generic argument(s) for 'cli::array<Type,dimension> ^System::Array::ConvertAll(cli::array<TInput,1> ^,System::Converter<TInput,TOutput> ^)' What am I doing wrong?

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  • How to avoid "incomplete implementation" warning in partial base class

    - by garph0
    I have created a protocol that my classes need to implement, and then factored out some common functionality into a base class, so I did this: @protocol MyProtocol - (void) foo; - (void) bar; @end @interface Base <MyProtocol> @end @interface Derived_1 : Base @end @interface Derived_2 : Base @end @implementation Base - (void) foo{ //something foo } @end @implementation Derived_1 - (void) bar{ //something bar 1 } @end @implementation Derived_2 - (void) bar{ //something bar 2 } @end In this way in my code I use a generic id<MyProtocol>. The code works (as long as Base is not used directly) but the compiler chokes at the end of the implementation of Base with a warning: Incomplete implementation of class Base Is there a way to avoid this warning or, even better, a more proper way to obtain this partially implemented abstract base class behavior in Objc?

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  • c: memory allocation (what's going on)

    - by facha
    Hi, everyone Please take a look at this piece of code. I'm allocating one byte for the first variable and another byte for the second one. However, it seems like the compiler allocates more (or I'm missing something). The program outputs both strings, even though their length is more the one byte. void main() { char* some1 = malloc(1); sprintf(some1,"cool"); char* some2 = malloc(1); sprintf(some2,"face"); printf("%s ",some1); printf("%s\n",some2); } Please, could anyone spot some light on what's going on when memory is being allocated.

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  • Create a modifiable string literal in C++

    - by Anne
    Is it possible to create a modifiable string literal in C++? For example: char* foo[] = { "foo", "foo" }; char* afoo = foo[0]; afoo[2] = 'g'; // access violation This produces an access violation because the "foo"s are allocated in read only memory (.rdata section I believe). Is there any way to force the "foo"s into writable memory (.data section)? Even via a pragma would be acceptable! (Visual Studio compiler) I know I can do strdup and a number of other things to get around the problem, but I want to know specifically if I can do as I have asked. :)

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  • Can I use a static var to "cache" the result? C++

    - by flyout
    I am using a function that returns a char*, and right now I am getting the compiler warning "returning address of local variable or temporary", so I guess I will have to use a static var for the return, my question is can I make something like if(var already set) return var else do function and return var? This is my function: char * GetUID() { TCHAR buf[20]; StringCchPrintf(buf, 20*sizeof(char), TEXT("%s"), someFunction()); return buf; } And this is what I want to do: char * GetUID() { static TCHAR buf[20]; if(strlen(buf)!=0) return buf; StringCchPrintf(buf, 20*sizeof(char), TEXT("%s"), someFunction()); return buf; } Is this a well use of static vars? And should I use ZeroMemory(&buf, 20*sizeof(char))? I removed it because if I use it above the if(strlen...) my TCHAR length is never 0, should I use it below?

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  • C/C++: Scanning a TIFF file using LIBTIFF

    - by Matt07
    My problem is to scan a tiff image in C and get all the pixel value (let's say for saving them in a txt file) in C/C++. I scanned the web and i found a library named "TIFFLIB" that should do what i was looking for. I downloaded it using the ubuntu package manager, but the gcc doesn't recognize the library. How do i link the library to the compiler? Have I installed it correctly? Is there any better/easier way to do that?

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  • c++ when to put method out side the class

    - by user63898
    i saw that some times in c++ applications using only namespace declarations with header and source file like this : #ifndef _UT_ #define _UT_ #include <string> #include <windows.h> namespace UT { void setRootPath(char* program_path, char* file_path); char * ConvertStringToCharP(std::string str); }; #endif //and then in UT.cpp #include "UT.h" namespace UT { char * ConvertStringToCharP(std::string str) { char * writable = new char[str.size() + 1]; std::copy(str.begin(), str.end(), writable); writable[str.size()] = '\0'; return writable; } void setRootPath(char* program_path, char* file_path) { //... } } is it better then defining classic class with static methods? or just simple class ? dose this method has something better for the compiler linker ? the methods in this namespace are called allot of times .

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  • ASP.NET MVC4: How to convert an IEnumerable to a string for ViewBag

    - by sehummel
    This is what I'm trying to do, but it doesn't work: HardwareType hwt = new HardwareType { HType = "PC" }; IEnumerable<Hardware> Pcs = db.Hardware.Where(h => h.HardwareType.Contains(hwt)); ViewBag.Pcs = Pcs.ToString(); So how do I convert my IEnumerable to a string (or other primitive data type) so the compiler won't give me an error when I try to use it in my Razor? @foreach (var item in ViewBag.Pcs) { <li><a href="#" class="btn"><i class="icon-hdd"></i> @item.HType</a></li> }

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  • Eclipse RCP: How to troubleshoot plugin dependencies & classpath problems?

    - by paul
    I am working on an RCP project based on eclipse. It has been working fine but recently I thought I'd upgrade it to use a new eclipse version (3.2 - 3.5). After a bit of trouble, it seemed to be working fine. Then I did something. Don't know what. The end result is that I'm getting a classpath error when one of my plugins (A) tries to access a class in one of the dependent plugins (B) (also one of mine). As far as I can see, Plugin A has Plugin B in its' dependency list and the compiler shows no errors. To test, I created a new Plugin C with one class and accessed the class from Plugin A. That works fine. Does anyone have any hints for troubleshooting such issues? A checklist of settings to check? I've been stuggling with this for hours and getting nowhere! Particularly frustrating as it was working until I changed something! Thanks

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