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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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  • sequentially-consistent atomic load on x86

    - by axe
    Hello all, I'm interested in sequentially-consistent load operation on x86. As far as I see from assembler listing, generated by compiler it is implemented as a plain load on x86, however plain loads as far as I know guaranteed to have acquire semantics, while plain stores are guaranteed to have release. Sequentially-consistent store is implemented as locked xchg, while load as plain load. That sounds strange to me, could you please explain this in details? added Just found in internet, that sequentially-consistent atomic load could be done as simple mov as long as store is done with locked xchg, but there was no prove and no links to documentation. Do you know where can I read about that? Thanks in advance.

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  • My Delphi 7 application halts on Application.Initialize and does not return to next line

    - by m-abdi
    I have created an application on Delphi 7. my app had running fine since yesterday. I don't know what's happened yesterday which cause my application halts on Application.Initialize line in source code and does not return to next line when i trace the program. I can't run the created executable file from widows niether while the generated file does run on another machine correctly. here is the code where the compiler stops on it: program Info_Kiosk; uses SysUtils, Forms, ... (some other units) ; {$R *.res} begin Application.Initialize; Application.CreateForm(Tfrm_Main, frm_Main); any help would be appreciated

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  • How Iostream file is located in computer by c++ code during execution

    - by user3702024
    i want to know that in a c++ code during execution how iostream file is founded. we write #include in c++ program and i know about #include which is a preprocessor directive to load files and is a file name but i don't know that how that file is located. i have some questions in my mind... Is Standard library present in compiler which we are using? Is that file is present in standard library or in our computer? Can we give directory path to locate the file through c++ code if yes then how?

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  • Modify bash variables with sed

    - by Alexander Cska
    I am trying to modify a number of environmental variables containing predefined compiler flags. To do so, I tried using a bash loop that goes over all environmental variables listed with "env". for i in $(env | grep ipo | awk 'BEGIN {FS="="} ; { print $1 } ' ) do echo $(sed -e "s/-ipo/ / ; s/-axAVX/ /" <<< $i) done This is not working since the loop variable $i contains just the name of the environmental variable stored as a character string. I tried searching a method to convert a string into a variable but things started becoming unnecessary complicated. The basic problem is how to properly supply the environmental variable itself to sed. Any ideas how to properly modify my script are welcome. Thanks, Alex

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  • problem in getting value of the object attribute in flex

    - by madanmohan
    i have an xml which contains 'interface' sub tag, iam converting xml to object using SampleXmlDecoder. compiler did not allow me to access the value of the 'inteface' attrible of the resultobject. var xml:XML = event.result as XML; var xmlDoc : XMLDocument = new XMLDocument(xml.toString()); var decoder : SimpleXMLDecoder = new SimpleXMLDecoder(true) var resultObj : Object = decoder.decodeXML(xmlDoc); var o:Object = new Object(); o.someprop = resultObj.maintag.item.interface; its treating interface as keyword. can anyone tell me the solution for this. Thanks in advance

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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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  • Haskell: Problems with overloading: Interpreter can´t tell which + to use

    - by Ben
    Hi, I want to make functions Double - Double an instance of the Num typeclass. I want to define the sum of two functions as sum of their images. So I wrote instance Num Function where f + g = (\ x - (f x) + (g x)) Here the compiler complains he can´t tell whether I´m using Prelude.+ or Module.+ in the lambda expression. So I imported Prelude qualified as P and wrote instance Num Function where f + g = (\ x - (f x) P.+ (g x)) This compiles just fine, but when I try to add two functions in GHCi the interpreter complains again he can´t tell whether I´m using Prelude.+ or Module.+. Is there any way I can solve this problem?

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  • C++ object in memory

    - by Neo_b
    Hello. Is there a standard in storing a C++ objects in memory? I wish to set a char* pointer to a certain address in memory, so that I can read certain objects' variables directly from the memory byte by byte. When I am using Dev C++, the variables are stored one by one right in the memory address of an object in the order that they were defined. Now, can it be different while using a different compiler (like the variables being in a different order, or somewhere else)? Thank you in advance. :-)

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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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  • 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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  • What features of Scala cannot be translated to Java?

    - by Paul
    The Scala compiler compiles direct to Java byte code (or .NET CIL). Some of the features of Scala could be re-done in Java straightforwardly (e.g. simple for comprehensions, classes, translating anonymous/inner functionc etc). What are the features that cannot be translated that way? That is presumably mostly of academic interest. More usefully, perhaps, what are the key features or idioms of Scala that YOU use that cannot be easily represented in Java? Are there any the other way about? Things that can be done straightforwardly in Java that have no straightforward equivalent in Scala? Idioms in Java that don't translate?

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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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  • Query on the scope of local variables in C

    - by darkie15
    All, Consider the following code: void func(void) { int a; printf ("%d", a); } int main(int argc, char **argv) { int a = 3; func(); printf("%d", a); } According to my understanding, the output should be: <junk value><3> Can anyone please confirm my understanding? My basic query is, does the compiler refer to the outer scope for a variable that has been declared but not defined? Regards, darkie

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  • Contents changed(cleared?) when access the pointer returned by std::string::c_str()

    - by justamask
    string conf()     {         vector v;         //..         v = func(); //this function returns a vector         return v[1];     }     void test()     {         const char* p = conf().c_str();         // the string object will be alive as a auto var         // so the pointer should be valid till the end of this function,right?           // ... lots of steps, but none of them would access the pointer p         // when access p here, SOMETIMES the contents would change ... Why?         // the platform is solaris 64 bit         // compiler is sun workshop 12         // my code is compiled as  ELF 32-bit MSB relocatable SPARC32PLUS Version 1, V8+ Required         // but need to link with some shared lib which are ELF 32-bit MSB dynamic lib SPARC Version 1, dynamically linked, stripped     }

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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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  • 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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  • 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 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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  • 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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  • 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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  • What is the Effect of Declaring 'extern "C"' in the Header to a C++ Shared Library?

    - by Adam
    Based on this question I understand the purpose of the construct in linking C libraries with C++ code. Now suppose the following: I have a '.so' shared library compiled with a C++ compiler. The header has a 'typedef stuct' and a number of function declarations. If the header includes the extern "C" declaration... #ifdef __cplusplus extern "C" { #endif // typedef struct ...; // function decls #ifdef __cplusplus } #endif ... what is the effect? Specifically I'm wondering if there are any detrimental side effects of that declaration since the shared library is compiled as C++, not C. Is there any reason to have the extern "C" declaration in this case?

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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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  • Strange exception phenomenon in Windows 7

    - by Level 2
    I spot some interesting articles about exception handle in CodeProject http://www.codeproject.com/KB/cpp/seexception.aspx After reading, I decided to do some experiment. The first time I try to execute the following code char *p; p[0] = 0; The program died without question. But After several times when I executed the same problem binary code, it magically did fine. Even the following code is doing well. Any clue or explanation? char *p p[1000] = 'd'; cout<<p[1000]<<endl; My O/S is Windows 7 64bit and compiler is VS2008 rc1.

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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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