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  • What non-programming books should a programmer read to help develop programming/thinking skills?

    - by FeatureCreep
    There are a lot of questions about what programming books should be on the programmer's bookshelf. How about non-programming related books that can help you become a better programmer or developer? It would also be interesting to know why they would help. My first choice would be Sun Tzu's "Art of War" (however cliché), because it made it obvious that the success of any project depends on the strength of its weakest link (and warfare is a big project).

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  • How do you explain refactoring to a non-technical person?

    - by Benjol
    (This question was inspired by the most-voted answer here) How do you go about explaining refactoring (and technical debt) to a non-technical person (typically a PHB or customer)? ("What, it's going to cost me a month of your work with no visible difference?!") UPDATE Thanks for all the answers so far, I think this list will provide several useful analogies to which we can point the appropriate people (though editing out references to PHBs may be wise!)

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  • What non-programming books should a programmer read (that helps developing programming skills/thinking)?

    - by FeatureCreep
    There are a lot of questions about what programming books should be on the programmer's bookshelf. How about non-programming related books that can help you become a better programmer or developer? It would also be interesting to know why they would help. My first choice would be Sun Tzu's "Art of War" (however cliché), because it made it obvious that the success of any project depends on the strength of its weakest link (and warfare is a big project).

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  • How to fix: "NPMethod called on non-NPObject wrapped JSObject" error?

    - by chandra
    HI, I am trying to call a method defined in flash object from javascript (firefox-3.0/Linux) and getting the exception: "NPMethod called on non- NPObject wrapped JSObject". If I use eval on window.document.flash_object.func() it throws "NPMethod called on non-NPObject wrapped JSObject". Where as, if I define a javascript function in side the page as given below: function myFunc() { return flash_object.func(); } and later do a eval of window.document.myFunc() it works fine. I am running the two evals through a test framework called Selenium. [eval(window.document.flash_object.func()) and eval(window.document.myFunc())]. The issues seems to be issue with invoking the flash-object method without passing 'this' reference. Here is sample html/js code to reproduce this issue: "NPMethod called on non-NPObject wrapped JSObject". <script> function changeColor() { mymovie.changeColor(); } function getColorNP() { var func = mymovie.getColor; func(); } </script> <button type="button" onclick="getColorNP();">getColorNP</button> <button type="button" onclick="getColor();">getColor</button> getColorNP throws the exception Error: NPMethod called on non-NPObject wrapped JSObject! Source File: http://my.host/Colors/colors.html getColorNP throws the exception Error: NPMethod called on non-NPObject wrapped JSObject! Source File: http://my.host/Colors/colors.html Now, question to javascript gurus: Given flash object and a method name, how do I invoke the method on that object. Lets say, a function takes two arguments: a flash object, and a method name as string. I want to do an eval on object.method() inside that function. Is this possible, if so, can you please explain me how this can be done. As flash object's method is not a standard javascript function, i think its not possible to function binding through bind(). Is there any other alternative? Thx, Chandra

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  • overriding ctype<wchar_t>

    - by Potatoswatter
    I'm writing a lambda calculus interpreter for fun and practice. I got iostreams to properly tokenize identifiers by adding a ctype facet which defines punctuation as whitespace: struct token_ctype : ctype<char> { mask t[ table_size ]; token_ctype() : ctype<char>( t ) { for ( size_t tx = 0; tx < table_size; ++ tx ) { t[tx] = isalnum( tx )? alnum : space; } } }; (classic_table() would probably be cleaner but that doesn't work on OS X!) And then swap the facet in when I hit an identifier: locale token_loc( in.getloc(), new token_ctype ); … locale const &oldloc = in.imbue( token_loc ); in.unget() >> token; in.imbue( oldloc ); There seems to be surprisingly little lambda calculus code on the Web. Most of what I've found so far is full of unicode ? characters. So I thought to try adding Unicode support. But ctype<wchar_t> works completely differently from ctype<char>. There is no master table; there are four methods do_is x2, do_scan_is, and do_scan_not. So I did this: struct token_ctype : ctype< wchar_t > { typedef ctype<wchar_t> base; bool do_is( mask m, char_type c ) const { return base::do_is(m,c) || (m&space) && ( base::do_is(punct,c) || c == L'?' ); } const char_type* do_is (const char_type* lo, const char_type* hi, mask* vec) const { base::do_is(lo,hi,vec); for ( mask *vp = vec; lo != hi; ++ vp, ++ lo ) { if ( *vp & punct || *lo == L'?' ) *vp |= space; } return hi; } const char_type *do_scan_is (mask m, const char_type* lo, const char_type* hi) const { if ( m & space ) m |= punct; hi = do_scan_is(m,lo,hi); if ( m & space ) hi = find( lo, hi, L'?' ); return hi; } const char_type *do_scan_not (mask m, const char_type* lo, const char_type* hi) const { if ( m & space ) { m |= punct; while ( * ( lo = base::do_scan_not(m,lo,hi) ) == L'?' && lo != hi ) ++ lo; return lo; } return base::do_scan_not(m,lo,hi); } }; (Apologies for the flat formatting; the preview converted the tabs differently.) The code is WAY less elegant. I does better express the notion that only punctuation is additional whitespace, but that would've been fine in the original had I had classic_table. Is there a simpler way to do this? Do I really need all those overloads? (Testing showed do_scan_not is extraneous here, but I'm thinking more broadly.) Am I abusing facets in the first place? Is the above even correct? Would it be better style to implement less logic?

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  • pointer being freed was not allocated. Complex malloc history help

    - by Martin KS
    I've followed the guides helpfully linked here: http://stackoverflow.com/questions/295778/iphone-debugging-pointer-being-freed-was-not-allocated-errors but the malloc_history is really throwing me for a loop, can anyone shed any light on the following: ALLOC 0x185c600-0x18605ff [size=16384]: thread_a068a4e0 |start | main | UIApplicationMain | -[UIApplication _run] | CFRunLoopRunInMode | CFRunLoopRunSpecific | PurpleEventCallback | _UIApplicationHandleEvent | -[UIApplication sendEvent:] | -[UIApplication handleEvent:withNewEvent:] | -[UIApplication _reportAppLaunchFinished] | CA::Transaction::commit() | CA::Context::commit_transaction(CA::Transaction*) | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CA::Context::commit_layer(_CALayer*, unsigned int, unsigned int, void*) | CA::Render::encode_set_object(CA::Render::Encoder*, unsigned long, unsigned int, CA::Render::Object*, unsigned int) | CA::Render::Layer::encode(CA::Render::Encoder*) const | CA::Render::Image::encode(CA::Render::Encoder*) const | CA::Render::Encoder::encode_data_async(void const*, unsigned long, void (*)(void const*, void*), void*) | CA::Render::Encoder::encode_bytes(void const*, unsigned long) | CA::Render::Encoder::grow(unsigned long) | realloc | malloc_zone_realloc ---- FREE 0x185c600-0x18605ff [size=16384]: thread_a068a4e0 |start | main | UIApplicationMain | -[UIApplication _run] | CFRunLoopRunInMode | CFRunLoopRunSpecific | PurpleEventCallback | _UIApplicationHandleEvent | -[UIApplication sendEvent:] | -[UIApplication handleEvent:withNewEvent:] | -[UIApplication _reportAppLaunchFinished] | CA::Transaction::commit() | CA::Context::commit_transaction(CA::Transaction*) | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CA::Context::commit_layer(_CALayer*, unsigned int, unsigned int, void*) | CA::Render::encode_set_object(CA::Render::Encoder*, unsigned long, unsigned int, CA::Render::Object*, unsigned int) | CA::Render::Layer::encode(CA::Render::Encoder*) const | CA::Render::Image::encode(CA::Render::Encoder*) const | CA::Render::Encoder::encode_data_async(void const*, unsigned long, void (*)(void const*, void*), void*) | CA::Render::Encoder::encode_bytes(void const*, unsigned long) | CA::Render::Encoder::grow(unsigned long) | realloc | malloc_zone_realloc ALLOC 0x185e000-0x185e62f [size=1584]: thread_a068a4e0 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __NSFireDelayedPerform | -[UITableView _userSelectRowAtIndexPath:] | -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] | -[PLAlbumView tableView:didSelectRowAtIndexPath:] | -[PLUIAlbumViewController albumView:selectedPhoto:] | PLNotifyImagePickerOfImageAvailability | -[UIImagePickerController _imagePickerDidCompleteWithInfo:] | -[GalleryViewController imagePickerController:didFinishPickingMediaWithInfo:] | UIImageJPEGRepresentation | CGImageDestinationFinalize | _CGImagePluginWriteJPEG | writeOne | _cg_jpeg_start_compress | _cg_jinit_compress_master | _cg_jinit_c_prep_controller | alloc_sarray | alloc_large | malloc | malloc_zone_malloc ---- FREE 0x185e000-0x185e62f [size=1584]: thread_a068a4e0 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __NSFireDelayedPerform | -[UITableView _userSelectRowAtIndexPath:] | -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] | -[PL AlbumView tableView:didSelectRowAtIndexPath:] | -[PLUIAlbumViewController albumView:selectedPhoto:] | PLNotifyImagePickerOfImageAvailability | -[UIImagePickerController _imagePickerDidCompleteWithInfo:] | -[GalleryViewController imagePickerController:didFinishPickingMediaWithInfo:] | UIImageJPEGRepresentation | CGImageDestinationFinalize | _CGImagePluginWriteJPEG | writeOne | _cg_jpeg_abort | free_pool | free ALLOC 0x185c800-0x185ea1f [size=8736]: thread_a068a4e0 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __NSFireDelayedPerform | -[UITableView _userSelectRowAtIndexPath:] | -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] | -[PLAlbumView tableView:didSelectRowAtIndexPath:] | -[PLUIAlbumViewController albumView:selectedPhoto:] | PLNotifyImagePickerOfImageAvailability | -[UIImagePickerController _imagePickerDidCompleteWithInfo:] | -[GalleryViewController imagePickerController:didFinishPickingMediaWithInfo:] | -[UIImage initWithData:] | _UIImageRefFromData | CGImageSourceCreateImageAtIndex | makeImagePlus | _CGImagePluginInitJPEG | initImageJPEG | calloc | malloc_zone_calloc

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  • C# wrapper and Callbacks

    - by fergs
    I'm in the process of writing a C# wrapper for Dallmeier Common API light (Camera & Surviellance systems) and I've never written a wrapper before, but I have used the Canon EDSDK C# wrapper. So I'm using the Canon wrapper as a guide to writing the Dallmeier wrapper. I'm currently having issues with wrapping a callback. In the API manual it has the following: dlm_connect int(unsigned long uLWindowHandle, const char * strIP, const char* strUser1, const char* strPwd1, const char* strUser2, const char* strPwd2, void (*callback)(void *pParameters, void *pResult, void *pInput), void * pInput) Arguments - ulWindowhandle - handle of the window that is passed to the ViewerSDK to display video and messages there - strUser1/2 - names of the users to log in. If only single user login is used strUser2 is - NULL - strPwd1/2 - passwords of both users. If strUser2 is NULL strPwd2 is ignored. Return This function creates a SessionHandle that has to be passed Callback pParameters will be structured: - unsigned long ulFunctionID - unsigned long ulSocketHandle, //handle to socket of the established connection - unsigned long ulWindowHandle, - int SessionHandle, //session handle of the session created - const char * strIP, - const char* strUser1, - const char* strPwd1, - const char* strUser2, - const char * strPWD2 pResult is a pointer to an integer, representing the result of the operation. Zero on success. Negative values are error codes. So from what I've read on the Net and Stack Overflow - C# uses delegates for the purpose of callbacks. So I create a my Callback function : public delegate uint DallmeierCallback(DallPparameters pParameters, IntPtr pResult, IntPtr pInput); I create the connection function [DllImport("davidapidis.dll")] public extern static int dlm_connect(ulong ulWindowHandle, string strIP, string strUser1, string strPwd1, string strUser2, string strPwd2, DallmeierCallback inDallmeierFunc And (I think) the DallPParameters as a struct : [StructLayout(LayoutKind.Sequential)] public struct DallPParameters { public ulong ulfunctionID; public ulong ulsocketHandle; public ulong ulWindowHandle; ... } All of this is in my wrapper class. Am I heading in the right direction or is this completely wrong?

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  • Instruments (Leaks) and NSDateFormatter

    - by Cal
    When I run my iPhone app with Instruments Leaks and parse a bunch of NSDates using NSDateFormatter my memory goes up about 1mb and stays even though these NSDates should be dealloc'd after the parsing (I just discard them if they aren't new). I thought the malloc (in my heaviest stack trace below) could become part of the NSDate but I also thought it could be memory that only used during some intermediate step in parsing. Does anyone know which one it is or how to find out? Also, is there a way to put a breakpoint on NSDate dealloc to see if that memory is really being reclaimed? Here's what my date formatter looks like for parsing these dates: df = [[NSDateFormatter alloc] init]; [df setDateFormat:@"EEE, d MMM yyyy H:m:s z"]; Here's the Heaviest Stack trace when the memory bumps up and stays there: 0 libSystem.B.dylib 208.80 Kb malloc 1 libicucore.A.dylib 868.19 Kb icu::ZoneMeta::getSingleCountry(icu::UnicodeString const&, icu::UnicodeString&) 2 libicucore.A.dylib 868.66 Kb icu::ZoneMeta::getSingleCountry(icu::UnicodeString const&, icu::UnicodeString&) 3 libicucore.A.dylib 868.67 Kb icu::ZoneMeta::getSingleCountry(icu::UnicodeString const&, icu::UnicodeString&) 4 libicucore.A.dylib 868.67 Kb icu::DateFormatSymbols::initZoneStringFormat() 5 libicucore.A.dylib 868.67 Kb icu::DateFormatSymbols::getZoneStringFormat() const 6 libicucore.A.dylib 868.67 Kb icu::SimpleDateFormat::subParse(icu::UnicodeString const&, int&, unsigned short, int, signed char, signed char, signed char*, icu::Calendar&) const 7 libicucore.A.dylib 868.67 Kb icu::SimpleDateFormat::parse(icu::UnicodeString const&, icu::Calendar&, icu::ParsePosition&) const 8 libicucore.A.dylib 868.67 Kb icu::DateFormat::parse(icu::UnicodeString const&, icu::ParsePosition&) const 9 libicucore.A.dylib 868.67 Kb udat_parse 10 CoreFoundation 868.67 Kb CFDateFormatterGetAbsoluteTimeFromString 11 CoreFoundation 868.67 Kb CFDateFormatterCreateDateFromString 12 Foundation 868.67 Kb -[NSDateFormatter getObjectValue:forString:range:error:] 13 Foundation 868.75 Kb -[NSDateFormatter getObjectValue:forString:errorDescription:] 14 Foundation 868.75 Kb -[NSDateFormatter dateFromString:] Thanks!

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  • How do I use a dependency on a Perl module installed in a non-standard location?

    - by Kinopiko
    I need to install two Perl modules on a web host. Let's call them A::B and X::Y. X::Y depends on A::B (needs A::B to run). Both of them use Module::Install. I have successfully installed A::B into a non-system location using perl Makefile.PL PREFIX=/non/system/location make; make test; make install Now I want to install X::Y, so I try the same thing perl Makefile.PL PREFIX=/non/system/location The output is $ perl Makefile.PL PREFIX=/non/system/location/ Cannot determine perl version info from lib/X/Y.pm *** Module::AutoInstall version 1.03 *** Checking for Perl dependencies... [Core Features] - Test::More ...loaded. (0.94) - ExtUtils::MakeMaker ...loaded. (6.54 >= 6.11) - File::ShareDir ...loaded. (1.00) - A::B ...missing. ==> Auto-install the 1 mandatory module(s) from CPAN? [y] It can't seem to find A::B in the system, although it is installed, and when it tries to auto-install the module from CPAN, it tries to write it into the system directory (ignoring PREFIX). I have tried using variables like PERL_LIB and LIB on the command line, after PREFIX=..., but nothing I have done seems to work. I can do make and make install successfully, but I can't do make test because of this problem. Any suggestions? I found some advice at http://servers.digitaldaze.com/extensions/perl/modules.html to use an environment variable PERL5LIB, but this also doesn't seem to work: export PERL5LIB=/non/system/location/lib/perl5/ didn't solve the problem.

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  • Please Help Me with my Homework Problem in C++

    - by sil3nt
    Hey there, this is part of a question i got in class, im at the final stretch but this has become a major problem. In it im given a certain value which is called the "gold value" and it is 40.5, this value changes in input. and i have these constants const int RUBIES_PER_DIAMOND = 5; // relative values. * const int EMERALDS_PER_RUBY = 2; const int GOLDS_PER_EMERALDS = 5; const int SILVERS_PER_GOLD = 4; const int COPPERS_PER_SILVER = 5; const int DIAMOND_VALUE = 50; // gold values. * const int RUBY_VALUE = 10; const int EMERALD_VALUE = 5; const float SILVER_VALUE = 0.25; const float COPPER_VALUE = 0.05; which means that basically for every diamond there are 5 rubies, and for every ruby there are 2 emeralds. So on and so forth. and the "gold value" for every diamond for example is 50 (diamond value = 50) this is how much one diamond is worth in golds. my problem is converting 40.5 into these diamonds and ruby values. I know the answer is 4rubies and 2silvers but how do i write the algorithm for this so that it gives the best estimate for every goldvalue that comes along??

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  • Memory leak in Qt signal and slots

    - by Ajay
    Hello, I am running valgrind on my Qt code,and even on successful exit of the application, get the following report from valgrind 8,832 bytes in 92 blocks are still reachable in loss record 12 of 12 at 0x4025390: operator new(unsigned int) (vg_replace_malloc.c:214) ==3339== by 0x4B75F05: QMutex::QMutex(QMutex::RecursionMode) (qmutex.cpp:123) ==3339== by 0x4B77602: QMutexPool::get(void const*) (qmutexpool.cpp:137) ==3339== by 0x4CA0EC2: signalSlotLock(QObject const*) (qobject.cpp:112) ==3339== by 0x4CA3939: QMetaObjectPrivate::connect(QObject const*, int, QObject const*, int, int, int*) (qobject.cpp:2900) ==3339== by 0x4CA5C00: QObject::connect(QObject const*, char const*, QObject const*, char const*, Qt::ConnectionType) (qobject.cpp:2599) I disconnect all signal connections and also delete the objects. The above mentioned leak increases if i increase the amount of signal and slot connections? Can anybody help with this?

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  • operator overloading of stream extraction operator in C++ help

    - by Crystal
    I'm having some trouble overloading my stream extraction operator in C++ for a hw assignment. I'm not really sure why I am getting these compile errors since I thought I was doing it right... Here is my code: Complex.h #ifndef COMPLEX_H #define COMPLEX_H class Complex { //friend ostream &operator<<(ostream &output, const Complex &complexObj) const; public: Complex(double = 0.0, double = 0.0); // constructor Complex operator+(const Complex &) const; // addition Complex operator-(const Complex &) const; // subtraction void print() const; // output private: double real; // real part double imaginary; // imaginary part }; #endif Complex.cpp #include <iostream> #include "Complex.h" using namespace std; // Constructor Complex::Complex(double realPart, double imaginaryPart) : real(realPart), imaginary(imaginaryPart) { } // addition operator Complex Complex::operator+(const Complex &operand2) const { return Complex(real + operand2.real, imaginary + operand2.imaginary); } // subtraction operator Complex Complex::operator-(const Complex &operand2) const { return Complex(real - operand2.real, imaginary - operand2.imaginary); } // Overload << operator ostream &Complex::operator<<(ostream &output, const Complex &complexObj) const { cout << '(' << complexObj.real << ", " << complexObj.imaginary << ')'; return output; // returning output allows chaining } // display a Complex object in the form: (a, b) void Complex::print() const { cout << '(' << real << ", " << imaginary << ')'; } main.cpp #include <iostream> #include "Complex.h" using namespace std; int main() { Complex x; Complex y(4.3, 8.2); Complex z(3.3, 1.1); cout << "x: "; x.print(); cout << "\ny: "; y.print(); cout << "\nz: "; z.print(); x = y + z; cout << "\n\nx = y + z: " << endl; x.print(); cout << " = "; y.print(); cout << " + "; z.print(); x = y - z; cout << "\n\nx = y - z: " << endl; x.print(); cout << " = "; y.print(); cout << " - "; z.print(); cout << endl; } Compile erros: complex.cpp(23) : error C2039: '<<' : is not a member of 'Complex' complex.h(5) : see declaration of 'Complex' complex.cpp(24) : error C2270: '<<' : modifiers not allowed on nonmember functions complex.cpp(25) : error C2248: 'Complex::real' : cannot access private member declared in class 'Complex' complex.h(13) : see declaration of 'Complex::real' complex.h(5) : see declaration of 'Complex' complex.cpp(25) : error C2248: 'Complex::imaginary' : cannot access private member declared in class 'Complex' complex.h(14) : see declaration of 'Complex::imaginary' complex.h(5) : see declaration of 'Complex' Thanks!

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  • Template with constant expression: error C2975 with VC++2008

    - by Arman
    Hello, I am trying to use elements of meta programming, but hit the wall with the first trial. I would like to have a comparator structure which can be used as following: intersect_by<ID>(L1.data, L2.data, "By ID: "); intersect_by<IDf>(L1.data, L2.data, "By IDf: "); Where: struct ID{};// Tag used for original IDs struct IDf{};// Tag used for the file position //following Boost.MultiIndex examples template<typename Tag,typename MultiIndexContainer> void intersect_by( const MultiIndexContainer& L1,const MultiIndexContainer& L2,std::string msg, Tag* =0 /* fixes a MSVC++ 6.0 bug with implicit template function parms / ) { / obtain a reference to the index tagged by Tag */ const typename boost::multi_index::index<MultiIndexContainer,Tag>::type& L1_ID_index= get<Tag>(L1); const typename boost::multi_index::index<MultiIndexContainer,Tag>::type& L2_ID_index= get<Tag>(L2); std::set_intersection( L1_ID_index.begin(), L1_ID_index.end(), L2_ID_index.begin(), L2_ID_index.end(), std::inserter(s, s.begin()), strComparator() // Here I get the C2975 error ); } template<int N> struct strComparator; template<> struct strComparator<0>{ bool operator () (const particleID& id1, const particleID& id2) const { return id1.ID struct strComparator<1{ bool operator () (const particleID& id1, const particleID& id2) const { return id1.IDf }; What I am missing? kind regards Arman.

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  • Compiler error when overwriting virtual methods

    - by Stefan Hubert
    Using VC71 compiler and get compiler errors, that i don't understand. Here comes the example class A { public: virtual int& myMethod() = 0; virtual const int& myMethod()const = 0; }; class B: public A { public: // generates: error C3241: 'const int &B::myMethod(void)' : this method was not introduced by 'A' virtual const int& A::myMethod() const; virtual int& A::myMethod(); }; when i switch order of both method definitions in B then I see a different compiler error: class B: public A { public: virtual const int& A::myMethod() const; // error C2556: 'const int &B::myMethod(void)' : overloaded function differs only by return type from 'int &B::myMethod(void)' // error C2373: 'B::myMethod' : redefinition; different type modifiers virtual int& A::myMethod(); }; however, if I omit the A:: stuff then i don't get any compiler error: class B: public A { public: virtual int& myMethod(); virtual const int& myMethod() const; }; So, what exactly does A:: in front of my method names and why do i see these diverse compiler errors? Any explanation welcome!

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  • Containers of reference_wrappers (comparison operators required?)

    - by kloffy
    If you use stl containers together with reference_wrappers of POD types, the following code works just fine: int i = 3; std::vector< boost::reference_wrapper<int> > is; is.push_back(boost::ref(i)); std::cout << (std::find(is.begin(),is.end(),i)!=is.end()) << std::endl; However, if you use non-POD types such as (contrived example): struct Integer { int value; bool operator==(const Integer& rhs) const { return value==rhs.value; } bool operator!=(const Integer& rhs) const { return !(*this == rhs); } }; It doesn't suffice to declare those comparison operators, instead you have to declare: bool operator==(const boost::reference_wrapper<Integer>& lhs, const Integer& rhs) { return boost::unwrap_ref(lhs)==rhs; } And possibly also: bool operator==(const Integer& lhs, const boost::reference_wrapper<Integer>& rhs) { return lhs==boost::unwrap_ref(rhs); } In order to get the equivalent code to work: Integer j = { 0 }; std::vector< boost::reference_wrapper<Integer> > js; js.push_back(boost::ref(j)); std::cout << (std::find(js.begin(),js.end(),j)!=js.end()) << std::endl; Now, I'm wondering if this is really the way it's meant to be done, since it seems impractical. It just seems there should be a simpler solution, e.g. templates: template<class T> bool operator==(const boost::reference_wrapper<T>& lhs, const T& rhs) { return boost::unwrap_ref(lhs)==rhs; } template<class T> bool operator==(const T& lhs, const boost::reference_wrapper<T>& rhs) { return lhs==boost::unwrap_ref(rhs); } There's probably a good reason why reference_wrapper behaves the way it does (possibly to accomodate non-POD types without comparison operators?). Maybe there already is an elegant solution and I just haven't found it.

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  • Implementing Operator Overloading with Logarithms in C++

    - by Jacob Relkin
    Hello my friends, I'm having some issues with implementing a logarithm class with operator overloading in C++. My first goal is how I would implement the changeBase method, I've been having a tough time wrapping my head around it. My secoond goal is to be able to perform an operation where the left operand is a double and the right operand is a logarithm object. Here's a snippet of my log class: // coefficient: double // base: unsigned int // number: double class _log { double coefficient, number; unsigned int base; public: _log() { base = rand(); coefficient = rand(); number = rand(); } _log operator+ ( const double b ) const; _log operator* ( const double b ) const; _log operator- ( const double b ) const; _log operator/ ( const double b ) const; _log operator<< ( const _log &b ); double getValue() const; bool changeBase( unsigned int base ); }; You guys are awesome, thank you for your time.

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  • Call the cast operator of template base class within the derived class

    - by yoni
    I have a template class, called Cell, here the definition: template <class T> class OneCell { ..... } I have a cast operator from Cell to T, here virtual operator const T() const { ..... } Now i have derived class, called DCell, here template <class T> class DCell : public Cell<T> { ..... } I need to override the Cell's cast operator (insert a little if), but after I need to call the Cell's cast operator. In other methods it's should be something like virtual operator const T() const { if (...) { return Cell<T>::operator const T; } else throw ... } but i got a compiler error error: argument of type 'const int (Cell::)()const' does not match 'const int' What can I do? Thank you, and sorry about my poor English.

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  • Why does virtual assignment behave differently than other virtual functions of the same signature?

    - by David Rodríguez - dribeas
    While playing with implementing a virtual assignment operator I have ended with a funny behavior. It is not a compiler glitch, since g++ 4.1, 4.3 and VS 2005 share the same behavior. Basically, the virtual operator= behaves differently than any other virtual function with respect to the code that is actually being executed. struct Base { virtual Base& f( Base const & ) { std::cout << "Base::f(Base const &)" << std::endl; return *this; } virtual Base& operator=( Base const & ) { std::cout << "Base::operator=(Base const &)" << std::endl; return *this; } }; struct Derived : public Base { virtual Base& f( Base const & ) { std::cout << "Derived::f(Base const &)" << std::endl; return *this; } virtual Base& operator=( Base const & ) { std::cout << "Derived::operator=( Base const & )" << std::endl; return *this; } }; int main() { Derived a, b; a.f( b ); // [0] outputs: Derived::f(Base const &) (expected result) a = b; // [1] outputs: Base::operator=(Base const &) Base & ba = a; Base & bb = b; ba = bb; // [2] outputs: Derived::operator=(Base const &) Derived & da = a; Derived & db = b; da = db; // [3] outputs: Base::operator=(Base const &) ba = da; // [4] outputs: Derived::operator=(Base const &) da = ba; // [5] outputs: Derived::operator=(Base const &) } The effect is that the virtual operator= has a different behavior than any other virtual function with the same signature ([0] compared to [1]), by calling the Base version of the operator when called through real Derived objects ([1]) or Derived references ([3]) while it does perform as a regular virtual function when called through Base references ([2]), or when either the lvalue or rvalue are Base references and the other a Derived reference ([4],[5]). Is there any sensible explanation to this odd behavior?

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  • Seeking STL-aware c++filt

    - by Don Wakefield
    In my development environment, I'm compiling a code base using GNU C++ 3.4.6. Code is under development, and unfortunately crashes now and then. It's nice to be able to run the traceback through a demangler, and I use c++filt 3.4. The problem comes when functions have a number of STL parameters. Consider My_callback::operator()( Status&, std::set<std::string> const&, std::vector<My_parameter*> const&, My_attribute_set const&, std::vector<My_parameter_base*> const&, std::vector<My_parameter> const&, std::set<std::string> const& ) { // ... } When this function is in the traceback, the mangled output on my platform is: (_ZN30My_callbackclER11StatusRKSt3setISsSt4lessISsESaISsEERKSt6vectorIP13My_parameterSaISB_EERK17My_attribute_setRKS9_IP18My_parameter_baseSaISK_EERKS9_ISA_SaISA_EES8_+0x76a) [0x13ffdaa] c++filt kindly demangles it to (My_callback::operator()(Status&, std::set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, std::vector<My_parameter*, std::allocator<My_parameter*> > const&, My_attribute_set const&, std::vector<My_parameter_base*, std::allocator<My_parameter_base*> > const&, std::vector<My_parameter, std::allocator<My_parameter> > const&, std::set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&)+0x76a) [0x13ffdaa] This is the same problem as compiler errors encountered when using templates. However, the STL is a fairly regular and recognizable package of templates. So what I'm hoping is that someone out there has created an enhanced version of c++filt which would dump something closer to the original function signature. Any hints?

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  • Internal class and access to external members.

    - by Knowing me knowing you
    I always thought that internal class has access to all data in its external class but having code: template<class T> class Vector { template<class T> friend std::ostream& operator<<(std::ostream& out, const Vector<T>& obj); private: T** myData_; std::size_t myIndex_; std::size_t mySize_; public: Vector():myData_(nullptr), myIndex_(0), mySize_(0) { } Vector(const Vector<T>& pattern); void insert(const T&); Vector<T> makeUnion(const Vector<T>&)const; Vector<T> makeIntersection(const Vector<T>&)const; class Iterator : public std::iterator<std::bidirectional_iterator_tag,T> { private: T** itData_; public: Iterator()//<<<<<<<<<<<<<------------COMMENT { /*HERE I'M TRYING TO USE ANY MEMBER FROM Vector<T> AND I'M GETTING ERR SAYING: ILLEGAL CALL OF NON-STATIC MEMBER FUNCTION*/} Iterator(T** ty) { itData_ = ty; } Iterator operator++() { return ++itData_; } T operator*() { return *itData_[0]; } bool operator==(const Iterator& obj) { return *itData_ == *obj.itData_; } bool operator!=(const Iterator& obj) { return *itData_ != *obj.itData_; } bool operator<(const Iterator& obj) { return *itData_ < *obj.itData_; } }; typedef Iterator iterator; iterator begin()const { assert(mySize_ > 0); return myData_; } iterator end()const { return myData_ + myIndex_; } }; See line marked as COMMENT. So can I or I can't use members from external class while in internal class? Don't bother about naming, it's not a Vector it's a Set. Thank you.

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  • Is there an use case for non-blocking receive when I have threads?

    - by Gabriel Šcerbák
    I know non-blocking receive is not used as much in message passing, but still some intuition tells me, it is needed. Take for example GUI event driven applications, you need some way to wait for a message in a non-blocking way, so your program can execute some computations. One of the ways to solve this is to have a special thread with message queue. Is there some use case, where you would really need non-blocking receive even if you have threads?

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  • I asked this yesterday, after the input given I'm still having trouble implementing..

    - by Josh
    I'm not sure how to fix this or what I did wrong, but whenever I enter in a value it just closes out the run prompt. So, seems I do have a problem somewhere in my coding. Whenever I run the program and input a variable, it always returns the same answer.."The content at location 76 is 0." On that note, someone told me that "I don't know, but I suspect that Program A incorrectly has a fixed address being branched to on instructions 10 and 11." - mctylr but I'm not sure how to fix that.. I'm trying to figure out how to incorporate this idea from R Samuel Klatchko.. I'm still not sure what I'm missing but I can't get it to work.. const int OP_LOAD = 3; const int OP_STORE = 4; const int OP_ADD = 5; ... const int OP_LOCATION_MULTIPLIER = 100; mem[0] = OP_LOAD * OP_LOCATION_MULTIPLIER + ...; mem[1] = OP_ADD * OP_LOCATION_MULTIPLIER + ...; operand = memory[ j ] % OP_LOCATION_MULTIPLIER; operation = memory[ j ] / OP_LOCATION_MULTIPLIER; I'm new to programming, I'm not the best, so I'm going for simplicity. Also this is an SML program. Anyway, this IS a homework assignment and I'm wanting a good grade on this. So I was looking for input and making sure this program will do what I'm hoping they are looking for. Anyway, here are the instructions: Write SML (Simpletron Machine language) programs to accomplish each of the following task: A) Use a sentinel-controlled loop to read positive number s and compute and print their sum. Terminate input when a neg number is entered. B) Use a counter-controlled loop to read seven numbers, some positive and some negative, and compute + print the avg. C) Read a series of numbers, and determine and print the largest number. The first number read indicates how many numbers should be processed. Without further a due, here is my program. All together. int main() { const int READ = 10; const int WRITE = 11; const int LOAD = 20; const int STORE = 21; const int ADD = 30; const int SUBTRACT = 31; const int DIVIDE = 32; const int MULTIPLY = 33; const int BRANCH = 40; const int BRANCHNEG = 41; const int BRANCHZERO = 41; const int HALT = 43; int mem[100] = {0}; //Making it 100, since simpletron contains a 100 word mem. int operation; //taking the rest of these variables straight out of the book seeing as how they were italisized. int operand; int accum = 0; // the special register is starting at 0 int j; // This is for part a, it will take in positive variables in a sent-controlled loop and compute + print their sum. Variables from example in text. memory [0] = 1010; memory [01] = 2009; memory [02] = 3008; memory [03] = 2109; memory [04] = 1109; memory [05] = 4300; memory [06] = 1009; j = 0; //Makes the variable j start at 0. while ( true ) { operand = memory[ j ]%100; // Finds the op codes from the limit on the memory (100) operation = memory[ j ]/100; //using a switch loop to set up the loops for the cases switch ( operation ){ case 10: //reads a variable into a word from loc. Enter in -1 to exit cout <<"\n Input a positive variable: "; cin >> memory[ operand ]; break; case 11: // takes a word from location cout << "\n\nThe content at location " << operand << "is " << memory[operand]; break; case 20:// loads accum = memory[ operand ]; break; case 21: //stores memory[ operand ] = accum; break; case 30: //adds accum += mem[operand]; break; case 31: // subtracts accum-= memory[ operand ]; break; case 32: //divides accum /=(memory[ operand ]); break; case 33: // multiplies accum*= memory [ operand ]; break; case 40: // Branches to location j = -1; break; case 41: //branches if acc. is < 0 if (accum < 0) j = 5; break; case 42: //branches if acc = 0 if (accum == 0) j = 5; break; case 43: // Program ends exit(0); break; } j++; } return 0; }

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