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  • C++, create an instance from a static method

    - by Manux
    Hello, let's say I want my users to use only one class, say SpecialData. Now, this data class would have many methods, and depending on the type of data, the methods do different things, internally, but return externally similar results. Therefore my wanting to have one "public" class and other "private", child classes that would change the behavior of methods, etc... It would be amazingly more simple for some types of data that need to be built to do something like this: SpecialData& sm = SpecialData::new_supermatrix(); and new_supermatrix() would return a SuperMatrix instance, which inherits from most behaviors of SpecialData. my header: static SpecialData& new_supermatrix(); my cpp: SpecialData& SpecialData::new_supermatrix()(){ return SuperMatrix(MATRIX_DEFAULT_MAGNITUDE,1000,1239,FLOAT32,etc...); } The problem is, I get this error, which is probably logical due to the circumstances: invalid initialization of non-const reference of type ‘SpecialData&’ from a temporary of type ‘SpecialData’ So, any ideas?

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  • Better way of enforcing this template?

    - by Dennis Ritchie
    Currently, I have a function template like this that converts a vector into a string (just a natural string, separating the elements with a comma): //the type T must be passable into std::to_string template<typename T> std::string vec_to_str(const std::vector<T> &vec); As you can see, this is only meant for vectors whose elements can be passed into the built-in std::to_string function (such as int, double, etc.) Is it considered a good practice to document with comments the allowed T? If not, what should I do? Is it possible to enforce this in a better way?

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  • Problem with number/type of arguments passed to an overloaded c++ constructor wrapped with swig.

    - by MiKo
    I am trying to wrap a c++ class (let's call it "Spam") written by someone else with swig to expose it to Python. After solving several problems, I am able to import the module in python, but when I try to create an object of such class I obtain the following error: foo = Spam.Spam('abc',3) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "Spam.py", line 96, in __init__ this = _Spam.new_Spam(*args) NotImplementedError: Wrong number of arguments for overloaded function 'new_Spam'. Possible C/C++ prototypes are: Spam(unsigned char *,unsigned long,bool,unsigned int,SSTree::io_action,char const *) Spam(unsigned char *,unsigned long,bool,unsigned int,SSTree::io_action) Spam(unsigned char *,unsigned long,bool,unsigned int) Spam(unsigned char *,unsigned long,bool) Spam(unsigned char *,unsigned long) Googling around, I realized that the error is probably caused by the type of the arguments and not by the number (which is quite confusing), but I still cannot identify. I suspect the problem lies in passing a string as the first argument, but have no idea on how to fix it (keep in mind that I know almost no c/c++).

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  • Why do I get corrupt output on my file?

    - by Martin
    I have a simple program which I have compiled in both MinGW and Visual C++ 2008 Express, and both give an output file larger than 88200. When I set s = 0, both programs work as expected. What am I doing wrong? #include <fstream> using namespace std; int main(int argc, char *argv[]) { int i; short s; fstream f; f.open("test.raw", ios_base::out); for(i = 0; i < 44100; i++) { s = i & 0xFFFF; // PROBLEM? f.write(reinterpret_cast<const char *>(&s), sizeof(s)); } f.close(); return 0; }

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  • When do I need to deallocate memory? C++

    - by extintor
    I am using this code inside a class to make a webbrowser control visit a website: void myClass::visitWeb(const char *url) { WCHAR buffer[MAX_LEN]; ZeroMemory(buffer, sizeof(buffer)); MultiByteToWideChar(CP_ACP, MB_ERR_INVALID_CHARS, url, strlen(url), buffer, sizeof(buffer)-1); VARIANT vURL; vURL.vt = VT_BSTR; vURL.bstrVal = SysAllocString(buffer); // webbrowser navigate code... VariantClear(&vURL); } Do I need to do some memory deallocation here?, I see vURL is being deallocated by VariantClear but should I deallocate memory for buffer? I've been told that in another bool I have in the same app I shouldn't deallocate anything because everything clear out when the bool return true/false, but what happens on this void?

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  • Magick++ in VS2010 - unresolved external symbol

    - by FlashFan
    Hey guys! I'm trying to use ImageMagick Magick++ for a C++ Project in VS2010. I installed the Library from here: klick Then in my Project, I added c:/program files/ImageMagick-6.6.6-Q16/include to the include folders. Then I tried to use Magick++ with this code: #include <Magick++.h> void main(int argc, char ** argv){ InitializeMagick(*argv); } But this does not work! VS2010 returns the following errors: error LNK2001: unresolved external symbol "__declspec(dllimport) void __cdecl Magick::InitializeMagick(char const *)" (__imp_?InitializeMagick@Magick@@YAXPBD@Z) error LNK1120: 1 unresolved externals What am I doing wrong? Thanks very much for your help!

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  • hierarchical html listbox with mimicking file explorer level folding

    - by collapsar
    hello everybody, i'm looking for a technique to adapt a html listbox to hierarchical content with an unlimited number of levels ( const 1 would be sufficient ). hierarchy levels should be collapsible as in the usual file explorer views. the html listbox behaviour should be preserved / mimicked as comprehensively as possible. do you have a hint on where to find or how to implement this ? jquery solutions are fine. firefox 3.5+, ie 8+, safari 5 must be supported; opera 11, chrome 9 would be nice. as far as i understand the issue, listbox contents are rendered inside their own browser window sporting none of the standard window adornments. a hint on how to obtain a handle on this window in js would be a sufficient starting point, as well as correcting me in case i misconceived the browser behaviour. thanks in advance for your efforts, best regards, carsten

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  • encryption problem for wlan profile

    - by Jassi
    i am trying to encrypt keyMaterial element from wireless profile. so I want to convert byte array into OLECHAR but it is giving me wrong output not key sea the below code you may know the solution... DATA_BLOB in; DATA_BLOB out; BYTE pin=(BYTE)"FIPL2"; DWORD din=strlen((char*)pin)+1; in.pbData = pin; in.cbData = din; if(CryptProtectData(&in,L"what is it",NULL,NULL,NULL,0,&out)) { BYTE *b=out.pbData; USES_CONVERSION; bstr=SysAllocString(W2BSTR((const WCHAR *)b)); HRCALL(peSubS222->put_text(bstr), ""); SysFreeString(bstr); bstr=NULL; } else { cout<<"NOOOOOOOOOOOOOOOO :("; } what is missing please help me out

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  • How to look up an NHibernate entity's table mapping from the type of the entity?

    - by snicker
    Once I've mapped my domain in NHibernate, how can I reverse lookup those mappings somewhere else in my code? Example: The entity Pony is mapped to a table named "AAZF1203" for some reason. (Stupid legacy database table names!) I want to find out that table name from the NH mappings using only the typeof(Pony) because I have to write a query elsewhere. How can I make the following test pass? private const string LegacyPonyTableName = "AAZF1203"; [Test] public void MakeSureThatThePonyEntityIsMappedToCorrectTable() { string ponyTable = GetNHibernateTableMappingFor(typeof(Pony)); Assert.AreEqual(LegacyPonyTableName, ponyTable); } In other words, what does the GetNHibernateTableMappingFor(Type t) need to look like?

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  • Is a switch statment ok for 30 or so conditions?

    - by DeanMc
    I am in the final stages of creating an MP4 tag parser in .Net. For those who have experience with tagging music you would be aware that there are an average of 30 or so tags. If tested out different types of loops and it seems that a switch statement with Const values seems to be the way to go with regard to catching the tags in binary. The switch allows me to search the binary without the need to know which order the tags are stored or if there are some not present but I wonder if anyone would be against using a switch statement for so many conditionals. Any insight is much appreciated.

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  • Context Menu event with QGraphicsWidget

    - by onurozcelik
    In my application I subclass QGraphicsWidget In paint I am drawing a line with pen width 4. I reimplemented boundingRect() and shape(). But I can't catch context menu event every time I click right mouse button. What is the problem.(Pen Width ? ) //Sample code for boundingRect() and shape() QRectF boundingRect() const { qreal rectLeft = x1 < x2 ? x1 : x2; qreal rectTop = y1 < y2 ? y1 : y2; qreal rectWidth = (x1 - x2) != 0 ? abs(x1-x2) : 4; qreal rectHeight = (y1 - y2) != 0 ? abs(y1 -y2) : 4; return QRectF(rectLeft,rectTop,rectWidth,rectHeigt); } QPainterPath shape() { QPainterPath path; path.addRect(boundingRect()); return path; }

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  • Where does output of print in kernel go?

    - by apoorv020
    I am debugging a driver for linux (specifically ubuntu server 9.04), and there are several printf statements in the code. Where can I view the output of these statements? EDIT1: What i'm trying to do is write to kernel using the proc file-system. The print code is static int proc_fractel_config_write(struct file *file, const char *argbuf, unsigned long count, void *data) { printk(KERN_DEBUG "writing fractel config\n"); ... In kern.log when I see the following message when i try to overwrite the file /proc/net/madwifi/ath1/fractel_config (with varying time of course). [ 8671.924873] proc write [ 8671.924919] Any explainations?

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  • += Overloading in C++ problem.

    - by user69514
    I am trying to overload the += operator for my rational number class, but I don't believe that it's working because I always end up with the same result: RationalNumber RationalNumber::operator+=(const RationalNumber &rhs){ int den = denominator * rhs.denominator; int a = numerator * rhs.denominator; int b = rhs.numerator * denominator; int num = a+b; RationalNumber ratNum(num, den); return ratNum; } Inside main //create two rational numbers RationalNumber a(1, 3); a.print(); RationalNumber b(6, 7); b.print(); //test += operator a+=(b); a.print(); After calling a+=(b), a is still 1/3, it should be 25/21. Any ideas what I am doing wrong?

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  • Is there a way to serialize automatically enums as int?

    - by FireAphis
    Hello, Is there a way to serialize enums automatically as int? Every time I define a new enum and write std::stringstream stream; stream << myenum1; stream >> myenum2; the compiler complains that the operators << and are not defined. Do you know a way to tell the compiler to treat enums as plain int's? What makes the problem harder is that, actually, the serialization is inside a template. Something like this: template <typename T> void serialize(const T& value) { std::stringstream stream; stream << value; } So I cannot add any casts :( Maybe I can specialize it somehow? Thank you.

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  • Cant free memory.

    - by atch
    In code: int a[3][4] = {1,2,3,4, 5,6,7,8, 9,10,11,12}; template<class T, int row, int col> void invert(T a[row][col]) { T* columns = new T[col]; T* const free_me = columns; for (int i = 0; i < col; ++i) { for (int j = 0; j < row; ++j) { *columns = a[j][i]; ++columns;//SOMETIMES VALUE IS 0 } } delete[] free_me;//I'M GETTING ERROR OF HEAP ABUSE IN THIS LINE } int main(int argc, char* argv[]) { invert<int,3,4>(a); } I've observed that while iterating, value of variable columns equals zero and I think thats the problem. Thanks for your help.

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  • Quick, Beginner C++ Overloading Question - Getting the compiler to perceive << is defined for a spec

    - by Francisco P.
    Hello everyone. I edited a post of mine so I coul I overloaded << for a class, Score (defined in score.h), in score.cpp. ostream& operator<< (ostream & os, const Score & right) { os << right.getPoints() << " " << right.scoreGetName(); return os; } (getPoints fetches an int attribute, getName a string one) I get this compiling error for a test in main(), contained in main.cpp binary '<<' : no operator found which takes a right-hand operand of type 'Score' (or there is no acceptable conversion) How come the compiler doesn't 'recognize' that overload as valid? (includes are proper) Thanks for your time.

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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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  • staying within boundaries of image?

    - by codefail
    So I am to loop through copyFrom.pixelData and copy it into pixelData. I realize that I need to check the conditions of i and j, and have them not copy past the boundaries of pixelData[x][y], I need another 2 loops for that? I tried this, but was getting segmentation fault.. Is this the right approach? void Image::insert(int xoff, int yoff, const Image& copyFrom, Color notCopy) { for (int x = xoff; x < xoff+copyFrom.width; x++) { for (int y = yoff; y < yoff+copyFrom.height; y++) { for (int i = 0; i<width; i++){ for (int j = 0; j<height; j++){ if (copyFrom.pixelData[i][j].colorDistance(notCopy)>20 ) pixelData[x][y]=copyFrom.pixelData[i][j]; } } } } }

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  • C++ cin returns 0 for integer no matter what the user inputs

    - by kevin dappah
    No matter the cin it continues to to output 0 for score. Why is that? I tried returning the "return 0;" but still no go :/ #include "stdafx.h" #include <iostream> using namespace std; // Variables int enemiesKilled; const int KILLS = 150; int score = enemiesKilled * KILLS; int main() { cout << "How many enemies did you kill?" << endl; cin >> enemiesKilled; cout << "Your score: " << score << endl; return 0; }

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  • Static member object of a class in the same class

    - by Luv
    Suppose we have a class as class Egg { static Egg e; int i; Egg(int ii):i(ii) {} Egg(const Egg &); //Prevents copy-constructor to be called public: static Egg* instance() {return &e} }; Egg Egg::e(47); This code guarantees that we cannot create any object, but could use only the static object. But how could we declare static object of the same class in the class. And also one thing more since e is a static object, and static objects can call only static member functions, so how could the constructor been called here for static object e, also its constructors are private.

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  • How to fill a section within c++ string?

    - by stacker
    Having a string of whitespaces: string *str = new string(); str->resize(width,' '); I'd like to fill length chars at a position. In C it would look like memset(&str[pos],'#', length ); How can i achieve this with c++ string, I tried string& assign( const string& str, size_type index, size_type len ); but this seems to truncat the original string. Is there an easy C++ way to do this? Thanks.

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  • C# (ASP.Net) Linking selection values to constants in Codebehind

    - by jasonvogel
    ASPX Code <asp:RadioButtonList ID="rbServer" runat="server" > <asp:ListItem Value=<%=ServerDeveloper%>> Developer </asp:ListItemv <asp:ListItem Value="dev.ahsvendor.com"> dev.test.com</asp:ListItem> <asp:ListItem Value="staging.ahsvendor.com"> staging.test.com</asp:ListItem> </asp:RadioButtonList> ASPX.CS - Codebehind const string ServerDeveloper = "developer"; ASPX Error: Code blocks are not supported in this context. Question: So what is the correct way to tie an dropdown/radio buttion/... ASPX value to a constant that is shared with the CodeBehind code? I know that I could do rbServer.Add.Item("developer") [from the CodeBehind], but is there a way to achieve it from the Presentation side of things?

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  • boost timer usage question

    - by stefita
    I have a really simple question, yet I can't find an answer for it. I guess I am missing something in the usage of the boost timer.hpp. Here is my code, that unfortunately gives me an error message: include <boost/timer.hpp> int main() { boost::timer t; } And the error messages are as follows: /usr/include/boost/timer.hpp: In member function ‘double boost::timer::elapsed_max() const’: /usr/include/boost/timer.hpp:59: error: ‘numeric_limits’ is not a member of ‘std’ /usr/include/boost/timer.hpp:59: error: ‘::max’ has not been declared /usr/include/boost/timer.hpp:59: error: expected primary-expression before ‘double’ /usr/include/boost/timer.hpp:59: error: expected `)' before ‘double’ The used library is boost 1.36 (SUSE 11.1). Thanks in advance!

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  • Any way to avoid a filesort when order by is different to where clause?

    - by Julian
    I have an incredibly simple query (table type InnoDb) and EXPLAIN says that MySQL must do an extra pass to find out how to retrieve the rows in sorted order. SELECT * FROM `comments` WHERE (commentable_id = 1976) ORDER BY created_at desc LIMIT 0, 5 exact explain output: table select_type type extra possible_keys key key length ref rows comments simple ref using where; using filesort common_lookups common_lookups 5 const 89 commentable_id is indexed. Comments has nothing trick in it, just a content field. The manual suggests that if the order by is different to the where, there is no way filesort can be avoided. http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html I also tried order by id as well as it's equivalent but makes no difference, even if I add id as an index (which I understand is not required as id is indexed implicitly in MySQL). thanks in advance for any ideas!

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  • Calling some functions before main in C

    - by minjang
    I'd like to do some stuffs before main function. I have multiple source files. In each file, there is some work that needs to be done before main. It was no problem in C++, but problematic with C. In C++, this can be done by two ways: Exploiting a constructor of a global class/struct. Calling a function to a global variable For example, static const int __register_dummy_ = __AddRegisterMetaInfo(...); However, in C, either ways is impossible. Obviously, there is no constructor. So, the first option is inherently impossible. I thought that the second option would be possible, but not compiled in C (I tested only with Visual C++. It gives C2099.). C only allows a constant to a non-automatic variable. Is there any way to call some functions before main?

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