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• Is there a standard literal constant that I can use instead of "utf-8" in C# (.Net 3.5)?

  - by Hamish Grubijan

  Hi, I would like to find a better way to do this: XmlNode nodeXML = xmlDoc.AppendChild( xmlDoc.CreateXmlDeclaration( "1.0", "utf-8", String.Empty) ); I do not want to think about "utf-8" vs "UTF-8" vs "UTF8" vs "utf8" as I type code. I would like to make my code less prone to typos. I am sure that some standard library has declatred "utf-8" as a const / readonly string. How can I find it? Also, what about "1.0"? I am assuming that major XML versions have been enumerated somewhere as well. Thanks!

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• How return a std::string from C's "getcwd" function

  - by rubenvb

  Sorry to keep hammering on this, but I'm trying to learn :). Is this any good? And yes, I care about memory leaks. I can't find a decent way of preallocating the char*, because there simply seems to be no cross-platform way. const string getcwd() { char* a_cwd = getcwd(NULL,0); string s_cwd(a_cwd); free(a_cwd); return s_cwd; } UPDATE2: without Boost or Qt, the most common stuff can get long-winded (see accepted answer)

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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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• C++ initializing constants and inheritance

  - by pingvinus

  I want to initialize constant in child-class, instead of base class. And use it to get rid of dynamic memory allocation (I know array sizes already, and there will be a few child-classes with different constants). So I try: class A { public: const int x; A() : x(0) {} A(int x) : x(x) {} void f() { double y[this->x]; } }; class B : A { B() : A(2) {} }; Pretty simple, but compiler says: error C2057: expected constant expression How can I say to compiler, that it is really a constant?

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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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• 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 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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• Retain cycle on `self` with blocks

  - by Jonathan Sterling

  I'm afraid this question is pretty basic, but I think it's relevant to a lot of Objective-C programmers who are getting into blocks. What I've heard is that since blocks capture local variables referenced within them as const copies, using self within a block can result in a retain cycle, should that block be copied. So, we are supposed to use __block to force the block to deal directly with self instead of having it copied. __block typeof(self) bself = self; [someObject messageWithBlock:^{ [bself doSomething]; }]; instead of just [someObject messageWithBlock:^{ [self doSomething]; }]; What I'd like to know is the following: if this is true, is there a way that I can avoid the ugliness (aside from using GC)?

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• Multiplying complex with constant in C++

  - by Atilla Filiz

  The following code fails to compile #include <iostream> #include <cmath> #include <complex> using namespace std; int main(void) { const double b=3; complex <double> i(0, 1), comp; comp = b*i; comp=3*i; return 0; } with error: no match for ‘operator*’ in ‘3 * i’ What is wrong here, why cannot I multiply with immediate constants?

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• Implementing implicitly shared classes outside of Qt

  - by Timothy Baldridge

  I'm familiar with the way Qt uses D-pointers for managing data. How do I do this in my code? I tried this method: 1) move all data into a struct 2) add a QAtomicInt to the struct 3) implement a = operator and change my constructor/deconstructor to check-up on the reference count. The issue is, when I go to do a shallow copy of the object, I get an error about QObject declaring = as private. How then do I accomplish this? Here's an example of my copy operator: HttpRequest & HttpRequest::operator=(const HttpRequest &other) { other.d->ref.ref(); if (!d->ref.deref()) delete d; d = other.d; return *this; } Am I going about this the wrong way?

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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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• Template class implicit copy constructor issues

  - by Nate

  Stepping through my program in gdb, line 108 returns right back to the calling function, and doesn't call the copy constructor in class A, like (I thought) it should: template <class S> class A{ //etc... A( const A & old ){ //do stuff... } //etc... }; template <class T> class B{ //etc... A<T> ReturnsAnA(){ A<T> result; // do some stuff with result return result; //line 108 } //etc... }; Any hints? I've banged my head against the wall about this for 4 hours now, and can't seem to come up with what's happening here.

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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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• How to free an Oracle Object-Type passed to an external procedure

  - by chila

  I'm using OTT to pass and load an Object Type from a C++ external procedure. The problem I have is that I don't know how to somehow mark the object for deallocation once extproc has done marshalling it. The object remains in extproc's memory forever making it grow in memory consumtion. Here's part of the code: void decodeFromBuffer(OCIExtProcContext *ctx, GPRS_GPRSCHARGINGRECORD *record, GPRS_GPRSCHARGINGRECORD_ind *recordInd, const unsigned char *buffer, int buffLen, OCIInd *bufferInd) { . . . assert(OCIExtProcGetEnv(ctx, &envh, &svch, &errh) == OCI_SUCCESS); recordInd->_atomic = OCI_IND_NOTNULL; // somehow I should mark the object for deallocation after extproc has done marshalling it // using OCINumberFromInt and OCIStringAssignText to load the object (this memory is never deallocated) . . . } How could I mark the object (and subobjects) for deallocation?

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• the problem only happens when i try create a release...

  - by ace

  I'm sorry if im not presenting this right, but i trully cannot understand what the problem is. i have a project to hand in, a code of 600 lines defined within a main, .cpp, and header file. if i compile the project with just a debugger and no release, it's fine. when i create it with the release, the following error occurs, for every function!!! 1st error: |36|multiple definition of `countLines(int&, std::vector const&)'| 2nd error: |36|first defined here| if someone will allow me and i can send them the entire code, that would be awesome - i have to have this done within 3 hours.

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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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• STL member variable initalization issue with windows API

  - by Django

  I am creating a windows app that uses a vector of stings as a member variable. For some reason, I can compile but when it tries to get at any of the vectors members is crashes. the error is 0xC0000005: Access violation reading location 0xcdcdcdd9. in the member function of the vector class. this is the size() function where it breaks. size_type capacity() const { // return current length of allocated storage return (this->_Myend - this->_Myfirst); } I am using visual studios 2010. thank you Django

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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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• Check if a SQL table exists.

  - by Carra

  What's the best way to check if a table exists in a Sql database in a database independant way? I came up with: bool exists; const string sqlStatement = @"SELECT COUNT(*) FROM my_table"; try { using (OdbcCommand cmd = new OdbcCommand(sqlStatement, myOdbcConnection)) { cmd.ExecuteScalar(); exists = true; } } catch (Exception ex) { exists = false; } Is there a better way to do this? This method will not work when the connection to the database fails. I've found ways for Sybase, SQL server, Oracle but nothing that works for all databases.

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• Linq to SQL Strange SQL Translation

  - by Master Morality

  I have a simple query that is generating some odd SQL translations, which is blowing up my code when the object is saturated. from x in DataContext.MyEntities select new { IsTypeCDA = x.EntityType == "CDA" //x.EntityType is a string and EntityType.CDA is a const string... } I would expect this query should translate to: SELECT (CASE WHEN [t0].[EntityType] = @p1 THEN 1 ELSE 0 END) as [IsTypeCDA] ... Instead I get this : SELECT (CASE WHEN @p1 = [t0].[EntityType] THEN 1 WHEN NOT (@p1 = [t0].[EntityType]) THEN 0 ELSE NULL END) AS [IsTypeCDA] ... Since I'm saturating a POCO where IsTypeCDA is a bool, it blows up stating I can't assign null to bool. Any thoughts? Edit: fixed the property names so they make sense...

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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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• Accessing Password Protected Network Drives in Windows in C#?

  - by tkeE2036

  Hi Everyone, So in C# I am trying to access a file on a network, for example at "//applications/myapp/test.txt", as follows: const string fileLocation = @"//applications/myapp/test.txt"; using (StreamReader fin = new StreamReader(FileLocation)) { while(!fin.EndOfStream()){ //Do some cool stuff with file } } However I get the following error: System.IO.IOException : Logon failure: unknown user name or bad password. I figure its because I need to supply some network credentials but I'm not sure how to get those to work in this situation. Does anyone know the best way (or any way) to gain access to these files that are on a a password protected location? Thanks in advance!!

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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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• Boost singleton and undefined reference

  - by Ockonal

  Hello, I globally use singleton pattern in my project. To make it easier - boost::singleton. Current project uses Ogre3d library for rendering. Here is some class: class GraphicSystem : public singleton<GraphicSystem> { private: Ogre::RenderWindow *mWindow; public: Ogre::RenderWindow *getWindow() const { return mWindow; } }; In GraphicSystem constructor I fill the mWindow value: mWindow = mRoot->createRenderWindow(...); I cheked it, everything makes normally. So, now I have to use handler for the window in input system (to get window handle). Somewhere else in another class: Ogre::RenderWindow *temp = GraphicSystem::get_mutable_instance().getWindow(); GraphicSystem::get_mutable_instance().getWindow()->getCustomAttribute("WINDOW", &mWindowHandle); temp is 0x00, and there is segfault at last line (getting custon attribute). I can't understand, why does singleton returns undefined pointer for the window. All another singleton-based classes work well.

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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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