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  • Operator() as a subscript (C++)

    - by Ivan Gromov
    I use operator() as a subscript operator this way: double CVector::operator() (int i) const { if (i >= 0 && i < this->size) return this->data[i]; else return 0; } double& CVector::operator() (int i) { return (this->data[i]); } It works when I get values, but I get an error when I try to write assign a value using a(i) = 1; UPD: Error text: Unhandled exception at 0x651cf54a (msvcr100d.dll) in CG.exe: 0xC0000005: Access violation reading location 0xccccccc0.

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  • Need to create a string token dynamically base on which method is calling it

    - by sa
    This is a minimal code. I have the string Str which is used by various methods. I want to in getId method be able to do 2 things Assign class="PDP" to it and Give it a value3 So the final string looks like <tr class='PDP' id='{2}'> <td {0}</td><td>{1}</td></tr> But please note that I will need different values for class in different methods so some Str will have PDP, another will have PTM etc. Is there a clean way to achieve this . private const string Str = "<tr><td >{0}</td><td>{1}</td></tr>"; public static string getId() { string field=string.Format(str, value1,value2, found=true? value3:""); }

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  • How can I require an attribute on a class definition?

    - by spoulson
    Is there a way to enforce a compile requirement for certain attributes on a class or interface implementation? For example, let's say my application uses a series of static classes that contain const int resource values. I'd like to decorate the class in a Description attribute to describe its contents. In concept, I'd like to apply this attribute requirement to an interface, then each static class would implement it with its required Description. I could write a run-time check or a unit test to check compliance. But really a compile-time check would be best. Is there such a thing?

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  • Does a static object within a function introduce a potential race condition?

    - by Jeremy Friesner
    I'm curious about the following code: class MyClass { public: MyClass() : _myArray(new int[1024]) {} ~MyClass() {delete [] _myArray;} private: int * _myArray; }; // This function may be called by different threads in an unsynchronized manner void MyFunction() { static const MyClass _myClassObject; [...] } Is there a possible race condition in the above code? Specifically, is the compiler likely to generate code equivalent to the following, "behind the scenes"? void MyFunction() { static bool _myClassObjectInitialized = false; if (_myClassObjectInitialized == false) { _myClassObjectInitialized = true; _myClassObject.MyClass(); // call constructor to set up object } [...] } ... in which case, if two threads were to call MyFunction() nearly-simultaneously, then _myArray might get allocated twice, causing a memory leak? Or is this handled correctly somehow?

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  • How to resolve error "Run-Time Check Failure #3"?

    - by karikari
    I am working on MS Visual Studio. I keep on getting this error: "Run-Time Check Failure #3 - The variable 'test' is being used without being initialized." I don't have any idea how to solve this. Here is the code that I'm currently tries to modify: STDMETHODIMP CButtonDemoBHO::Exec(const GUID*, DWORD nCmdID, DWORD d, VARIANTARG*, VARIANTARG* pvaOut) { CRebarHandler *test; switch (nCmdID){ case BUTTON_PRESSED: MessageBox(m_hWnd, L"You have pressed the button", L"Button Pressed", MB_OK); test->findButton(m_hWnd); test->setmenu(); break; case MENU_ITEM_SELECT: MessageBox(m_hWnd, L"You have simulated a button press with the menu ", L"Menu Pressed", MB_OK); break; } return S_OK; }

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  • Using .dll methods to load data from file in C# code

    - by Espinas.iss
    I want to use in C# these methods: * int LibRaw::open_datastream(LibRaw_abstract_datastream *stream) * int LibRaw::open_file(const char *rawfile) * int LibRaw::open_buffer(void *buffer, size_t bufsize) * int LibRaw::unpack(void) * int LibRaw::unpack_thumb(void) that are stored in a libraw.dll. These functions one by one load data from file... I've been reading about P/Invoke but i'm not sure how to invoke them. Can anyone show me an example how to use all of these functions together in C# to load file (raw image stored in folder) or just how to PIvoke one of them. Thanx!

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  • incorrect variable value outside main()

    - by cru3l
    i have this code #import <Foundation/Foundation.h> int testint; NSString *teststring; int Test() { NSLog(@"%d",testint); NSLog(@"%@",teststring); } int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; testint = 5; NSString *teststring = [[NSString alloc] initWithString:@"test string"]; Test(); [pool drain]; return 0; } in output i have: 5 (null) why Test function doesn't see correct teststring value? What should I do, to have correct "test string" in output?

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  • assignment vs std::swap and merging and keeping duplicates in seperate object

    - by rubenvb
    Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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  • C++0x, How do I expand a tuple into variadic template function arguments?

    - by Gustaf
    Consider the case of a templated function with variadic template arguments: template<typename Tret, typename... T> Tret func(const T&... t); Now, I have a tuple t of values. How do I call func() using the tuple values as arguments? I've read about the bind() function object, with call() function, and also the apply() function in different some now-obsolete documents. The GNU GCC 4.4 implementation seems to have a call() function in the bind() class, but there is very little documentation on the subject. Some people suggest hand-written recursive hacks, but the true value of variadic template arguments is to be able to use them in cases like above. Does anyone have a solution to is, or hint on where to read about it?

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  • How do I use "this" in a member function?

    - by Peter Stewart
    I've written a member function of class Node to read a tree of Nodes in postfix order. It will be called by the Node instance which is the root node of the tree. So: N.postfix(); these appear to be illeagal: *this->left.postfix(); *this->right.postfix(); What is the proper way to do this? class Node { public: const char *cargo; int depth; Node *left; Node *right void Node::postfix() { if (this==__nullptr) { return; } else { *this->left.postfix(); *this->right.postfix(); out<<*this->cargo<<"\n"; return; } };

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  • Reading in 4 bytes at a time

    - by alphomega
    I have a big file full of integers that I'm loading in. I've just started using C++, and I'm trying out the filestream stuff. From everything I've read, it appears I can only read in bytes, So I've had to set up a char array, and then cast it as a int pointer. Is there a way I can read in 4 bytes at a time, and eliminate the need for the char array? const int HRSIZE = 129951336; //The size of the table char bhr[HRSIZE]; //The table int *dwhr; int main() { ifstream fstr; /* load the handranks.dat file */ std::cout << "Loading table.dat...\n"; fstr.open("table.dat"); fstr.read(bhr, HRSIZE); fstr.close(); dwhr = (int *) bhr; }

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  • Creating ostream manipulators for a specific class

    - by petersohn
    I have a class that is derived from ostream: class my_ostream: public std::ostream { // ... } I want to make a manipulator (for example do_something), that works specifically to this class, like this: my_ostream s; s << "some text" << do_something << "some more text"; I did the following: std::ostream &do_something(std::ostream &os) { my_ostream *s = dynamic_cast<my_ostream*>(&os); if (s != NULL) { // do something } return os; } This works, but is rather ugly. I tried the following: my_ostream &do_something(my_ostream &s) { // do something return s; } This doesn't work. I also tried another approach: class my_ostream: public std::ostream { // ... my_ostream &operator<<(const do_something & x) { // do something return *this; } } This still doesn't work.

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  • How to change FPU context in signal handler (C++/Linux)

    - by Henry Fané
    I wrote a signal handler to catch FPE errors. I need to continue execution even if this happens. I receive a ucontext_t as parameter, I can change the bad operand from 0 to another value but the FPU context is still bad and I run into an infinite loop ? Does someone already manupulate the ucontext_t structure on Linux ? I finally found a way to handle these situations by clearing the status flag of ucontext_t like this: ... const long int cFPUStatusFlag = 0x3F; aContext->uc_mcontext.fpregs->sw &= ~cFPUStatusFlag; ... 0x3F is negated to put 0 in the 6 bits of the status register of the FPU (x87). Doing this implies to check for FPE exceptions after calculation.

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  • string manipulations in C

    - by Vivek27
    Following are some basic questions that I have with respect to strings in C. If string literals are stored in read-only data segment and cannot be changed after initialisation, then what is the difference between the following two initialisations. char *string = "Hello world"; const char *string = "Hello world"; When we dynamically allocate memory for strings, I see the following allocation is capable enough to hold a string of arbitary length.Though this allocation work, I undersand/beleive that it is always good practice to allocate the actual size of actual string rather than the size of data type.Please guide on proper usage of dynamic allocation for strings. char *string = (char *)malloc(sizeof(char));

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  • How to get this to compile?

    - by ShaChris23
    I have this code which compiles and works as expected: class Right {}; class Left { public: Left& operator = (Right const&) { //... Do something ... return *this; } }; int main() { Right right; Left left; // Assign individual object -- this works left = right; } But now, this one surprises me, I thought the template would work itself out since I already provided the = operator() to the Left class. int main() { ... std::list<Right> rightLst; std::list<Left> leftLst; // Assign a list of objects -- this doesn't compile leftLst = rightLst; } What can I do so that I could convert the rightLst to leftLst conversion in a single line?

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  • strange results with /fp:fast

    - by martinus
    We have some code that looks like this: inline int calc_something(double x) { if (x > 0.0) { // do something return 1; } else { // do something else return 0; } } Unfortunately, when using the flag /fp:fast, we get calc_something(0)==1 so we are clearly taking the wrong code path. This only happens when we use the method at multiple points in our code with different parameters, so I think there is some fishy optimization going on here from the compiler (Microsoft Visual Studio 2008, SP1). Also, the above problem goes away when we change the interface to inline int calc_something(const double& x) { But I have no idea why this fixes the strange behaviour. Can anyone explane this behaviour? If I cannot understand what's going on we will have to remove the /fp:fastswitch, but this would make our application quite a bit slower.

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  • CryptGenRandom to generate asp.net session id

    - by DoDo
    Hi! does anyone have working example of CryptGenrRandom class to generate session id (need to use in my iis module). HCRYPTPROV hCryptProv; BYTE pbData[16]; if(CryptAcquireContext( &hCryptProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) { if(CryptGenRandom(hCryptProv, 8, pbData)) { std::string s(( const char *) pbData); printf(s.c_str()); } else { MyHandleError("Error during CryptGenRandom."); } } else { MyHandleError("Error during CryptAcquireContext!\n"); } i tried this code but, its not working quite well (i get it from msdn) and this example don't work for me ( http://www.codeproject.com/KB/security/plaintextsessionkey.aspx ) so if anyone know how to generate sessionid using this class plz let me know tnx anyway!

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  • setsockopt (sys/socket.h)

    - by lojin
    The prototype for setsockopt is: int setsockopt(int socket, int level, int option_name, const void *option_value, socklen_t option_len); Are the following all correct ? Which are not ? a.) int buffsize = 50000; setsockopt(s, SOL_SOCKET, SO_RCVBUF, (char *)&buffsize, sizeof(buffsize)); b.) int buffsize = 50000; setsockopt(s, SOL_SOCKET, SO_RCVBUF, (void *)&buffsize, sizeof(buffsize)); c.) char *buffsize = "50000"; setsockopt(s, SOL_SOCKET, SO_RCVBUF, buffsize, strlen(buffsize)); d.) setsockopt(s, SOL_SOCKET, SO_RCVBUF, "50000", 5);

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  • Objective C LValue required as unary '&' operand

    - by Bob
    Hello! In my code, I get this error when I try to get a pointer to my class property. (I wrote a small *.OBJ file translator in Python, discarding the normals) CODE: //line: line of text const char *str = [line UTF8String]; Point3D *p1, *p2, *p3; p1 = [Point3D makeX:0 Y:0 Z:0]; p2 = [Point3D makeX:0 Y:0 Z:0]; p3 = [Point3D makeX:0 Y:0 Z:0]; sscanf(str, "t %f,%f,%f %f,%f,%f %f,%f,%f",(&[p1 x]),&([p1 y]),&([p1 z]),&([p2 x]),&([p2 y]),&([p2 z]),&([p3 x]),&([p3 y]),&([p3 z])); Triangle3D *tri = [Triangle3D make:p1 p2:p2 p3:p3];

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  • How to build up a lookup table in microcontroller?

    - by GiGi
    Hi, I am so confused about how to build up a 3-dimension lookup table. Is the template as follows: create a 3 dimensional array to store data. Then create linked list. Then create function 'insert' to put all the data into the array? As some book said, linked list should be static const, is it need to create another function to expand the list? Because the lookup table should be used in a microcontroller, it only needs to finish the operation of putting the data into the array and whenever want to find the data, it will be fast and easy to search. Could you help me with that and give me some suggestions? Thank you.

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  • Reducing template bloat with inheritance

    - by benoitj
    Does anyone have experience reducing template code bloat using inheritance? i hesitate rewriting our containers this way: class vectorBase { public: int size(); void clear(); int m_size; void *m_rawData; //.... }; template< typename T > class vector : public vectorBase { void push_back( const T& ); //... }; I should keep maximum performance while reducing compile time I'm also wondering why stl implementations do not uses this approach Thanks for your feedbacks

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  • Trouble assigning a tr1::shared_ptr

    - by Max
    I've got a class that has a tr1::shared_ptr as a member, like so: class Foo { std::tr1::shared_ptr<TCODBsp> bsp; void Bar(); } In member function Bar, I try to assign it like this: bsp = newTCODBsp(x,y,w,h); g++ then gives me this error no match for ‘operator=’ in ‘((yarl::mapGen::MapGenerator*)this)->yarl::mapGen::MapGenerator::bsp = (operator new(40u), (<statement>, ((TCODBsp*)<anonymous>)))’ /usr/include/c++/4.4/tr1/shared_ptr.h:834: note: candidates are: std::tr1::shared_ptr<TCODBsp>& std::tr1::shared_ptr<TCODBsp>::operator=(const std::tr1::shared_ptr<TCODBsp>&) in my code, Foo is actually yarl::mapGen::MapGenerator. What am I doing wrong?

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  • parsing/matching string occurrence in C

    - by David
    I have the following string: const char *str = "\"This is just some random text\" 130 28194 \"Some other string\" \"String 3\"" I would like to get the the integer 28194 of course the integer varies, so I can't do strstr("20194"). So I was wondering what would be a good way to get that part of the string? I was thinking to use #include <regex.h> which I already have a procedure to match regexp's but not sure how the regexp in C will look like using the POSIX style notation. [:alpha:]+[:digit:] and if performance will be an issue. Or will it be better using strchr,strstr? Any ideas will be appreciate it

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  • Operator + for matrices in C++

    - by cibercitizen1
    I suppose the naive implementation of a + operator for matrices (2D for instance) in C++ would be: class Matrix { Matrix operator+ (Matrix other) const { Matrix result; // fill result with *this.data plus other.data return result; } } so we could use it like Matrix a; Matrix b; Matrix c; c = a + b; Right? But if matrices are big this is not efficient as we are doing one not-necessary copy (return result). Therefore, If we wan't to be efficient we have to forget the clean call: c = a + b; Right? What would you suggest / prefer ? Thanks.

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  • parsing Two-dimensional array in c

    - by gitter78
    I'm trying to parse an array that looks like the one below: char *arr[][2] = { { "1", "Purple" }, { "2", "Blue" }, { "22", "Red" }, ... }; I was thinking having a loop as: char *func(char *a){ for(i = 0; i<sizeof(arr)/sizeof(arr[0]);i++){ if(strstr(a,arr[i][0])!=NULL) return arr[i][1]; } } char *out; const char *hello = "this is my 2 string"; out = func(hello); In this case, I'm trying to get the second value based on the first one: Purple, Blue Red, etc.. The question is how would go in parsing this and instead of printing out the value, return the value. UPDATE/FIXED: It has been fixed above. Thanks

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