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• How do I make a class whose interface matches double, but upon which templates can be specialized?

  - by Neil G

  How do I make a class whose interface matches double, but whose templated types do not dynamic cast to double? The reason is that I have a run-time type system, and I want to be able to have a type that works just like double: template<int min_value, int max_value> class BoundedDouble: public double {}; And then inherit use template specialization to get run-time information about that type: template<typename T> class Type { etc. } template<int min_value, int max_value> class Type<BoundedDouble<min_value, max_value>> { int min() const { return min_value; } etc. } But, you can't inherit from double...

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• use callback function to report stack backtrace

  - by user353394

  Assume I have the following: typedef struct { char *name; char binding; int address; } Fn_Symbol //definition of function symbol static Fn_Symbol *fnSymbols; //array of function symbols in a file statc int total; //number of symbol functions in the array and file static void PrintBacktrace(int sigum, siginfo_t * siginfo, void *context) { printf("\nSignal received %d (%s)\n", signum, strsignal(signum)); const int eip_index = 14; void *eip = (void *)((struct ucontext *)context)->uc_mcontext.gregs[eip_index]; printf("Error at [%p] %s (+0x%x), eip, fnName, offset from start); //????? exit(0); } I have this so far, but what is the best way using the fnSymbols static global pointer to identify the function where the error occured and then back trace through the stack to identify each calling function by address, name, and offset?

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• Access violation reading location 0x00184000.

  - by numerical25

  having troubles with the following line HR(md3dDevice->CreateBuffer(&vbd, &vinitData, &mVB)); it appears the CreateBuffer method is having troubles reading &mVB. mVB is defined in box.h and looks like this ID3D10Buffer* mVB; Below is the code it its entirety. this is all files that mVB is in. //Box.cpp #include "Box.h" #include "Vertex.h" #include <vector> Box::Box() : mNumVertices(0), mNumFaces(0), md3dDevice(0), mVB(0), mIB(0) { } Box::~Box() { ReleaseCOM(mVB); ReleaseCOM(mIB); } float Box::getHeight(float x, float z)const { return 0.3f*(z*sinf(0.1f*x) + x*cosf(0.1f*z)); } void Box::init(ID3D10Device* device, float m, float n, float dx) { md3dDevice = device; mNumVertices = m*n; mNumFaces = 12; float halfWidth = (n-1)*dx*0.5f; float halfDepth = (m-1)*dx*0.5f; std::vector<Vertex> vertices(mNumVertices); for(DWORD i = 0; i < m; ++i) { float z = halfDepth - (i * dx); for(DWORD j = 0; j < n; ++j) { float x = -halfWidth + (j* dx); float y = getHeight(x,z); vertices[i*n+j].pos = D3DXVECTOR3(x, y, z); if(y < -10.0f) vertices[i*n+j].color = BEACH_SAND; else if( y < 5.0f) vertices[i*n+j].color = LIGHT_YELLOW_GREEN; else if (y < 12.0f) vertices[i*n+j].color = DARK_YELLOW_GREEN; else if (y < 20.0f) vertices[i*n+j].color = DARKBROWN; else vertices[i*n+j].color = WHITE; } } D3D10_BUFFER_DESC vbd; vbd.Usage = D3D10_USAGE_IMMUTABLE; vbd.ByteWidth = sizeof(Vertex) * mNumVertices; vbd.BindFlags = D3D10_BIND_VERTEX_BUFFER; vbd.CPUAccessFlags = 0; vbd.MiscFlags = 0; D3D10_SUBRESOURCE_DATA vinitData; vinitData.pSysMem = &vertices; HR(md3dDevice->CreateBuffer(&vbd, &vinitData, &mVB)); //create the index buffer std::vector<DWORD> indices(mNumFaces*3); // 3 indices per face int k = 0; for(DWORD i = 0; i < m-1; ++i) { for(DWORD j = 0; j < n-1; ++j) { indices[k] = i*n+j; indices[k+1] = i*n+j+1; indices[k+2] = (i*1)*n+j; indices[k+3] = (i*1)*n+j; indices[k+4] = i*n+j+1; indices[k+5] = (i*1)*n+j+1; k+= 6; } } D3D10_BUFFER_DESC ibd; ibd.Usage = D3D10_USAGE_IMMUTABLE; ibd.ByteWidth = sizeof(DWORD) * mNumFaces*3; ibd.BindFlags = D3D10_BIND_INDEX_BUFFER; ibd.CPUAccessFlags = 0; ibd.MiscFlags = 0; D3D10_SUBRESOURCE_DATA iinitData; iinitData.pSysMem = &indices; HR(md3dDevice->CreateBuffer(&ibd, &iinitData, &mIB)); } void Box::Draw() { UINT stride = sizeof(Vertex); UINT offset = 0; md3dDevice->IASetVertexBuffers(0, 1, &mVB, &stride, &offset); md3dDevice->IASetIndexBuffer(mIB, DXGI_FORMAT_R32_UINT, 0); md3dDevice->DrawIndexed(mNumFaces*3, 0 , 0); } //Box.h #ifndef _BOX_H #define _BOX_H #include "d3dUtil.h" Box.h class Box { public: Box(); ~Box(); void init(ID3D10Device* device, float m, float n, float dx); void Draw(); float getHeight(float x, float z)const; private: DWORD mNumVertices; DWORD mNumFaces; ID3D10Device* md3dDevice; ID3D10Buffer* mVB; ID3D10Buffer* mIB; }; #endif Thanks again for the help

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• Why does SQLite not bring back any results from my database

  - by tigermain

  This is my first SQLite based iPhone app and I am trying to get it to read a menu hierarchy from my database. The database appears to be registered fine as the compiled statement doesnt error (tried putting in valid table name to test) but for some reason sqlite3_step(compiledStmt) doesnt ever equal SQLITE_ROW as if to suggest there is no data in there; which there is. sqlite3 *database; menu = [[NSMutableArray alloc] init]; if (sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) { const char *sqlStmt = "SELECT * FROM Menu"; sqlite3_stmt *compiledStmt; if (sqlite3_prepare_v2(database, sqlStmt, -1, &compiledStmt, NULL) == SQLITE_OK) { while (sqlite3_step(compiledStmt) == SQLITE_ROW) { NSString *aTitle = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStmt, 1)]; MenuItem *menuItem = [[MenuItem alloc] init]; menuItem.title = aTitle; [menu addObject:menuItem]; [menuItem release]; } } else { NSLog(@"There is an error with the SQL Statement"); } sqlite3_finalize(compiledStmt); } sqlite3_close(database);

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• How do I simplify this templated vector initializer loop using lambdas or some kind of STL transform

  - by Neil G

  How do I simplify this templated vector initializer loop using lambdas or some kind of STL transform? template<typename T> template<typename... Args> DotProduct<T>::DotProduct(int n, RNG& rng, Args const&... args) { myBasis.resize(n); for (auto it = myBasis.begin(); it != myBasis.end(); ++it) { typename T::CPDDist cpd(rng, args...); *it = T(cpd); } }

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• Sql inline query with parameters. Parameter is not read when the query is executed.

  - by fzshah76

  Hi All: I am having a problem with my sql query in c#, basically it's inline query with parameters, but when I run it it tells me that parameter 1 or parameter 2 is not there here is my query declared on top of the page as public: public const string InsertStmtUsersTable = "insert into Users (username, password, email, userTypeID, memberID, CM7Register) " + "Values(@username, @password, @email, @userTypeID, @memberID,@CM7Register ); select @@identity"; this is my code for assigning the parameters, I know I am having problem so I am assigning the params twice: Username =(cmd.Parameters["@username"].Value = row["username"].ToString()) as string; cmd.Parameters["@username"].Value = row["username"].ToString(); In 1 methopd it calls this query and tries to insert to table, here is the code: Result = Convert.ToInt32(SqlHelper.ExecuteScalar(con, CommandType.Text,InsertStmtUsersTable)); Exact error message is: Must declare the variable '@username'.

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• Why won't C++ allow this default value

  - by nieldw

  Why won't GCC allow a default parameter here? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { This is the output I get: graph.h:82: error: default argument given for parameter 2 of ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool)’ graph.h:36: error: after previous specification in ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool)’ Can anyone see why I'm getting this?

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• read out a txt and send the last line to email adress - vbscript

  - by matthias

  Hallo, I'm back haha :-) so i have the next question and i hope someone can help me... I know i have a lot of questions but i will try to learn vbscript :-) Situation: I try to make a program that check all 5 min a txt and if there a new line in the txt, i'll try to send it to my eMail Address Option Explicit Dim fso, WshShell, Text, Last, objEmail Const folder = "C:\test.txt" Set fso=CreateObject("Scripting.FileSystemObject") Set WshShell = WScript.CreateObject("WScript.Shell") Do Text = Split(fso.OpenTextFile(Datei, 1).ReadAll, vbCrLF) Letzte = Text(UBound(Text)) Set objEmail = CreateObject("CDO.Message") objEmail.From = "[email protected]" objEmail.To = "[email protected]" objEmail.Subject = "Control" objEmail.Textbody = Last objEmail.Configuration.Fields.Item _ ("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2 objEmail.Configuration.Fields.Item _ ("http://schemas.microsoft.com/cdo/configuration/smtpserver") = _ "smtpip" objEmail.Configuration.Fields.Item _ ("http://schemas.microsoft.com/cdo/configuration/smtpserverport") = 25 objEmail.Configuration.Fields.Update objEmail.Send WScript.Sleep 300000 Loop This program works, but this program send me all 5 mins a mail...but i will only have a new mail when there is a new line in the txt. Can someone help me?

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• converting string to int in C++

  - by xbonez

  I am trying to convert a string I read in from a file to an int value so I can store it in an integer variable. This is what my code looks like: ifstream sin; sin.open("movie_output.txt"); string line; getline(sin,line); myMovie.setYear(atoi(line)); Over here, setYear is a mutator in the Movie class (myMovie is an object of Movie class) that looks like this: void Movie::setYear(unsigned int year) { year_ = year; } When I run the code, I get the following error: error C2664: 'atoi' : cannot convert parameter 1 from 'std::string' to 'const char *' 1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

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• How to load an RSA key from binary data to an RSA structure using the OpenSSL C Library?

  - by Andreas Bonini

  Currently I have my private key saved in a file, private.key, and I use the following function to load it: RSA *r = PEM_read_RSAPrivateKey("private.key", NULL, NULL, NULL); This works perfectly but I'm not happy with the file-based format; I want to save my key in pure binary form (ie, no base64 or similar) in a char* variable and load/save the key from/to it. This way I have much more freedom: I'll be able to store the key directly into the application const char key[] { 0x01, 0x02, ... };, send it over a network socket, etc. Unfortunately though I haven't found a way to do that. The only way to save and load a key I know of reads/saves it to a file directly.

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• how to open many files simultaneously for reading in c

  - by monkeyking

  I'm trying to port some of my c++ code into c. I have the following construct class reader{ private: FILE *fp; alot_of_data data;//updated by read_until() method public: reader(const char*filename) read_until(some conditional dependent on the contents of the file, and the arg supplied) } Im then instantiating hundreds of these object and iterate over them using several 'read_until()' for each file until allfiles is at eof. I'm failing to see any clever way to do this in c, the only solution I can come up with is making an array of FILE pointers, and do the same with all the private member data from my class. But this seems very messy, can I implement the functionality of my class as a function pointer, or anything better, I think I'm missing a fundamental design pattern? The files are way to big to have all in memory, so reading everything from every file is not feasible Thanks

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• Does C# compile code inside an if(false) block?

  - by aximili

  I am just wondering if these code blocks gets compiled into .dll I don't think this one gets compiled at all #if SOMETHING_UNDEFINED // some code - this is ignored by the compiler #endif Now what about these? 1. if(false) { // some code - is this compiled? } 2. const bool F = false; if(F) { // some code - is this compiled? } 3. bool F = false; if(F) { // some code - is this compiled? }

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• Multiple constructors definitions with same name but different signatures (C++)

  - by PuRe_ChAoS12

  With the following code, I keep getting error C2535 when I compile. It's complaining that a member function already defined or declared. Rationnel.h ... class Rationnel { public: Rationnel(int); //Constructor Rationnel(int,int); //Constructor void add(const Rationnel); ... Rationnel.cpp ... //Constructor Rationnel::Rationnel(int n = 1) { numerateur = n; denominateur = 1; } //Constructor Rationnel::Rationnel(int n = 1, int d = 1) { numerateur = n; denominateur = d; } ... Any idea what could be causing the error? Thanks for your time.

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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