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  • ActionScript Defining a Static Constant Array

    - by TheDarkIn1978
    is it not possible to define a static const array? i would like to have an optional parameter to a function that is an array of colors, private static const DEFAULT_COLORS:Array = new Array(0x000000, 0xFFFFFF); public function myConstructor(colorsArray:Array = DEFAULT_COLORS) { } i know i can use ...args but i actually wanting to supply the constructor with 2 separate arrays as option arguments.

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  • error CS0133: Assigning the result of a function to a const in C#.net

    - by Greg
    Trying to tidy up scope and avoid possible multiple calls to RegisterWindowMessage. Currently have a class used once with the following member [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)] static extern int RegisterWindowMessage(string lpString); private int m_message = RegisterWindowMessage("MY_MSG"); As we only have one instance this seems ok, but think it would be more tidy to use. With my basic C# understanding this should call RegisterWindowMessage and assign the result to int and not allow it to change. private const int message = RegisterWindowMessage("MY_MSG"); however attempting to do so leads to a error CS0133: The expression being assigned to 'someclass.messageEvent' must be constant so now I'm confused, does this mean the function was being assigned and called each time m_message was used previously, is there something else missing?

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  • Avoiding improper std::string initialization with NULL const char* using g++

    - by pachanga
    A there any g++ options which can detect improper initialization of std::string with NULL const char*? I was in the process of turning some int fields into std::string ones, i.e: struct Foo { int id; Foo() : id(0) {} }; ...turned into: struct Foo { std::string id; Foo() : id(0) {} //oooops! }; I completely overlooked bad 'id' initialization with 0 and g++ gave me no warnings at all. This error was detected in the run time(std::string constructor threw an exception) but I'd really like to detect such stuff in the compile time. Is there any way?

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  • C++ Ambiguous call to Overloaded Function (const variety)

    - by Joe
    After researching this online, I've only found solutions that don't apply to my problem, so please bear with me. Code snippet: typedef my_map_t<int const *, float> _test; my_map_t::const_iterator not_found = my_map_t::end(); if (_test.find(&iKeyValue) == not_found) { _test[iKeyValue] = 4 + 5; // not the actual code, but here for simplicity } The compiler complains that there's an ambiguous call to my_map_t::end(). This makes sense, because the only difference is the return type. Output: error C2668: 'std::_Tree<_Traits>::end' : ambiguous call to overloaded function Normally you can disambiguate the call by casting the parameters, but end() has no parameters. Any ideas?

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  • Unreachable code detected by using const variables

    - by Anton Roth
    I have following code: private const FlyCapture2Managed.PixelFormat f7PF = FlyCapture2Managed.PixelFormat.PixelFormatMono16; public PGRCamera(ExamForm input, bool red, int flags, int drawWidth, int drawHeight) { if (f7PF == FlyCapture2Managed.PixelFormat.PixelFormatMono8) { bpp = 8; // unreachable warning } else if (f7PF == FlyCapture2Managed.PixelFormat.PixelFormatMono16){ bpp = 16; } else { MessageBox.Show("Camera misconfigured"); // unreachable warning } } I understand that this code is unreachable, but I don't want that message to appear, since it's a configuration on compilation which just needs a change in the constant to test different settings, and the bits per pixel (bpp) change depending on the pixel format. Is there a good way to have just one variable being constant, deriving the other from it, but not resulting in an unreachable code warning? Note that I need both values, on start of the camera it needs to be configured to the proper Pixel Format, and my image understanding code needs to know how many bits the image is in. So, is there a good workaround, or do I just live with this warning?

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  • error: 'QTabWidget::QTabWidget(const QTabWidget&)' is private

    - by Mahdi_Nine
    I develop a program and I have 10 backups of it. I added some lines to it and when I compiled the project and now it has the following error: C:\Qt\Qt5.0.1\5.0.1\mingw47_32\include\QtWidgets\qtabwidget.h:173: error: 'QTabWidget::QTabWidget(const QTabWidget&)' is private the error is from * line namespace Ui { class ContentControl; } class ContentControl : public QTabWidget // * from this line { Q_OBJECT public: . . . } All backups have this error now. Any idea why? I re-installed Qt but the problem is still present.

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  • converting an array of characters to a const gchar*

    - by Mark Roberts
    I've got an array of characters which contains a string: char buf[MAXBUFLEN]; buf[0] = 'f'; buf[1] = 'o'; buf[2] = 'o'; buf[3] = '\0'; I'm looking to pass this string as an argument to the gtk_text_buffer_insert function in order to insert it into a GtkTextBuffer. What I can't figure out is how to convert it to a const gchar *, which is what gtk_text_buffer_insert expects as its third argument. Can anybody help me out?

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  • How to pass a const unsigned char * from c++ to c#

    - by tzup
    So I have a function in unmanaged c++ that gets called when some text happens to have "arrived": #using <MyParser.dll> ... void dump_body(const unsigned char *Body, int BodyLen) { // Need to pass the body to DumpBody, but as what type? ... lMyParser::Parser::DumpBody(???); } DumpBody is a function defined in a C# DLL that should take one parameter of type? Body holds an array of characters (text) of length BodyLen. There's obviously some marshalling to be done here but I have no idea how. Please help.

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  • Windows C++: LPCTSTR vs const TCHAR

    - by mrl33t
    In my application i'm declaring a string variable near the top of my code to define the name of my window class which I use in my calls to RegisterClassEx, CreateWindowEx etc.. Now, I know that an LPCTSTR is a typedef and will eventually follow down to a TCHAR (well a CHAR or WCHAR depending on whether UNICODE is defined), but I was wondering whether it would be better to use this: static LPCTSTR szWindowClass = TEXT("MyApp"); Or this: static const TCHAR szWindowClass[] = TEXT("MyApp"); I personally prefer the use of the LPCTSTR as coming from a JavaScript, PHP, C# background I never really considered declaring a string as an array of chars. But are there actually any advantages of using one over the other, or does it in fact not even make a difference as to which one I choose? Thank you, in advanced, for your answers.

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  • std::cin >> *aa results in a bus error

    - by Koning Baard XIV
    I have this a class called PPString: PPString.h #ifndef __CPP_PPString #define __CPP_PPString #include "PPObject.h" class PPString : public PPObject { char *stringValue[]; public: char *pointerToCharString(); void setCharString(char *charString[]); void setCharString(const char charString[]); }; #endif PPString.cpp #include "PPString.h" char *PPString::pointerToCharString() { return *stringValue; } void PPString::setCharString(char *charString[]) { *stringValue = *charString; } void PPString::setCharString(const char charString[]) { *stringValue = (char *)charString; } I'm trying to set the stringValue using std::cin: main.cpp PPString myString; myString.setCharString("LOLZ"); std::cout << myString.pointerToCharString() << std::endl; char *aa[1000]; std::cin >> *aa; myString.setCharString(aa); std::cout << myString.pointerToCharString() << std::endl; The first one, which uses a const char works, but the second one, with a char doesn't, and I get this output: copy and paste from STDOUT LOLZ im entering a string now... Bus error where the second line is what I entered, followed by pressing the return key. Can anyone help me fixing this? Thanks...

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  • I can't get that `bus error` to stop sucking.

    - by Koning Baard XIV
    I have this a class called PPString: PPString.h #ifndef __CPP_PPString #define __CPP_PPString #include "PPObject.h" class PPString : public PPObject { char *stringValue[]; public: char *pointerToCharString(); void setCharString(char *charString[]); void setCharString(const char charString[]); }; #endif PPString.cpp #include "PPString.h" char *PPString::pointerToCharString() { return *stringValue; } void PPString::setCharString(char *charString[]) { *stringValue = *charString; } void PPString::setCharString(const char charString[]) { *stringValue = (char *)charString; } I'm trying to set the stringValue using std::cin: main.cpp PPString myString; myString.setCharString("LOLZ"); std::cout << myString.pointerToCharString() << std::endl; char *aa[1000]; std::cin >> *aa; myString.setCharString(aa); std::cout << myString.pointerToCharString() << std::endl; The first one, which uses a const char works, but the second one, with a char doesn't, and I get this output: copy and paste from STDOUT LOLZ im entering a string now... Bus error where the second line is what I entered, followed by pressing the return key. Can anyone help me fixing this? Thanks...

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  • C++ variable to const expression

    - by user1344784
    template <typename Real> class A{ }; template <typename Real> class B{ }; //... a few dozen more similar template classes class Computer{ public slots: void setFrom(int from){ from_ = from; } void setTo(int to){ to_ = to; } private: template <int F, int T> void compute(){ using boost::fusion::vector; using boost::fusion::at_c; vector<A<float>, B<float>, ...> v; at_c<from_>(v).operator()(at_c<to_>(v)); //error; needs to be const-expression. }; This question isn't about Qt, but there is a line of Qt code in my example. The setFrom() and setTo() are functions that are called based on user selection via the GUI widget. The root of my problem is that 'from' and 'to' are variables. In my compute member function I need to pick a type (A, B, etc.) based on the values of 'from' and 'to'. The only way I know how to do what I need to do is to use switch statements, but that's extremely tedious in my case and I would like to avoid. Is there anyway to convert the error line to a constant-expression?

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  • Error "initializer element is not constant" when trying to initialize variable with const

    - by tomlogic
    I get an error on line 6 (initialize my_foo to foo_init) of the following program and I'm not sure I understand why. typedef struct foo_t { int a, b, c; } foo_t; const foo_t foo_init = { 1, 2, 3 }; foo_t my_foo = foo_init; int main() { return 0; } Keep in mind this is a simplified version of a larger, multi-file project I'm working on. The goal was to have a single constant in the object file, that multiple files could use to initialize a state structure. Since it's an embedded target with limited resources and the struct isn't that small, I don't want multiple copies of the source. I'd prefer not to use: #define foo_init { 1, 2, 3 } I'm also trying to write portable code, so I need a solution that's valid C89 or C99. Does this have to do with the ORGs in an object file? That initialized variables go into one ORG and are initialized by copying the contents of a second ORG? Maybe I'll just need to change my tactic, and have an initializing function do all of the copies at startup. Unless there are other ideas out there?

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  • Boost Python - Limits to the number of arguments when wrapping a function

    - by Derek
    I'm using Boost Python to wrap some C++ functions that I've created. One of my C++ functions contains 22 arguments. Boost complains when I try to compile my solution with this function, and I'm trying to figure out if it is just because this function has too many arguments. Does anyone know if such a limit exists? I've copied the error I'm getting below, not the code because I figure someone either knows the answer to this or not - and if there is no limit then I'll just try to figure it out myself. Thanks very much in advance! Here is a copy of the beginning of the error message I receive... 1>main.cpp 1>c:\cpp_ext\boost\boost_1_47\boost\python\make_function.hpp(76): error C2780: 'boost::mpl::vector17<RT,most_derived<Target,ClassT>::type&,T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14> boost::python::detail::get_signature(RT (__thiscall ClassT::* )(T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14) volatile const,Target *)' : expects 2 arguments - 1 provided 1>c:\cpp_ext\boost\boost_1_47\boost\python\signature.hpp(236) : see declaration of 'boost::python::detail::get_signature' And eventually I get about a hundred copies of error messages very much resembling this one: 1>c:\cpp_ext\boost\boost_1_47\boost\python\make_function.hpp(76): error C2784: 'boost::mpl::vector17<RT,ClassT&,T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14> boost::python::detail::get_signature(RT (__thiscall ClassT::* )(T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14) volatile const)' : could not deduce template argument for 'RT (__thiscall ClassT::* )(T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14) volatile const' from 'std::string (__cdecl *)(const std::string &,jal::date::JULIAN_DATE,const std::string &,const std::string &,int,const std::string &,const std::string &,const std::string &,const std::string &,const std::string &,const std::string &,int,const std::string &,const std::string &,int,const std::string &,const std::string &,const std::string &,const std::string &,const std::string &,int,const std::string &)' 1> c:\cpp_ext\boost\boost_1_47\boost\python\signature.hpp(218) : see declaration of 'boost::python::detail::get_signature' 1>c:\cpp_ext\boost\boost_1_47\boost\python\make_function.hpp(76): error C2780: 'boost::mpl::vector17<RT,most_derived<Target,ClassT>::type&,T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14> boost::python::detail::get_signature(RT (__thiscall ClassT::* )(T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14) volatile,Target *)' : expects 2 arguments - 1 provided 1> c:\cpp_ext\boost\boost_1_47\boost\python\signature.hpp(236) : see declaration of 'boost::python::detail::get_signature'

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  • C++ non-member functions for nested template classes

    - by beldaz
    I have been writing several class templates that contain nested iterator classes, for which an equality comparison is required. As I believe is fairly typical, the comparison is performed with a non-member (and non-friend) operator== function. In doing so, my compiler (I'm using Mingw32 GCC 4.4 with flags -O3 -g -Wall) fails to find the function and I have run out of possible reasons. In the rather large block of code below there are three classes: a Base class, a Composed class that holds a Base object, and a Nested class identical to the Composed class except that it is nested within an Outer class. Non-member operator== functions are supplied for each. These classes are in templated and untemplated forms (in their own respective namespaces), with the latter equivalent to the former specialised for unsigned integers. In main, two identical objects for each class are compared. For the untemplated case there is no problem, but for the templated case the compiler fails to find operator==. What's going on? #include <iostream> namespace templated { template<typename T> class Base { T t_; public: explicit Base(const T& t) : t_(t) {} bool equal(const Base& x) const { return x.t_==t_; } }; template<typename T> bool operator==(const Base<T> &x, const Base<T> &y) { return x.equal(y); } template<typename T> class Composed { typedef Base<T> Base_; Base_ base_; public: explicit Composed(const T& t) : base_(t) {} bool equal(const Composed& x) const {return x.base_==base_;} }; template<typename T> bool operator==(const Composed<T> &x, const Composed<T> &y) { return x.equal(y); } template<typename T> class Outer { public: class Nested { typedef Base<T> Base_; Base_ base_; public: explicit Nested(const T& t) : base_(t) {} bool equal(const Nested& x) const {return x.base_==base_;} }; }; template<typename T> bool operator==(const typename Outer<T>::Nested &x, const typename Outer<T>::Nested &y) { return x.equal(y); } } // namespace templated namespace untemplated { class Base { unsigned int t_; public: explicit Base(const unsigned int& t) : t_(t) {} bool equal(const Base& x) const { return x.t_==t_; } }; bool operator==(const Base &x, const Base &y) { return x.equal(y); } class Composed { typedef Base Base_; Base_ base_; public: explicit Composed(const unsigned int& t) : base_(t) {} bool equal(const Composed& x) const {return x.base_==base_;} }; bool operator==(const Composed &x, const Composed &y) { return x.equal(y); } class Outer { public: class Nested { typedef Base Base_; Base_ base_; public: explicit Nested(const unsigned int& t) : base_(t) {} bool equal(const Nested& x) const {return x.base_==base_;} }; }; bool operator==(const Outer::Nested &x, const Outer::Nested &y) { return x.equal(y); } } // namespace untemplated int main() { using std::cout; unsigned int testVal=3; { // No templates first typedef untemplated::Base Base_t; Base_t a(testVal); Base_t b(testVal); cout << "a=b=" << testVal << "\n"; cout << "a==b ? " << (a==b ? "TRUE" : "FALSE") << "\n"; typedef untemplated::Composed Composed_t; Composed_t c(testVal); Composed_t d(testVal); cout << "c=d=" << testVal << "\n"; cout << "c==d ? " << (c==d ? "TRUE" : "FALSE") << "\n"; typedef untemplated::Outer::Nested Nested_t; Nested_t e(testVal); Nested_t f(testVal); cout << "e=f=" << testVal << "\n"; cout << "e==f ? " << (e==f ? "TRUE" : "FALSE") << "\n"; } { // Now with templates typedef templated::Base<unsigned int> Base_t; Base_t a(testVal); Base_t b(testVal); cout << "a=b=" << testVal << "\n"; cout << "a==b ? " << (a==b ? "TRUE" : "FALSE") << "\n"; typedef templated::Composed<unsigned int> Composed_t; Composed_t c(testVal); Composed_t d(testVal); cout << "c=d=" << testVal << "\n"; cout << "d==c ? " << (c==d ? "TRUE" : "FALSE") << "\n"; typedef templated::Outer<unsigned int>::Nested Nested_t; Nested_t e(testVal); Nested_t f(testVal); cout << "e=f=" << testVal << "\n"; cout << "e==f ? " << (e==f ? "TRUE" : "FALSE") << "\n"; // Above line causes compiler error: // error: no match for 'operator==' in 'e == f' } cout << std::endl; return 0; }

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  • ASP.NET-C#: Inserting const into TextBox in Gridview

    - by dash
    I have some problems inserting a const "1" into a textbox which is gridviw. the gridview code: <asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False" EnableViewState="False"> <Columns> <asp:BoundField DataField="Price" HeaderText="Price" ItemStyle-CssClass="price" > <ItemStyle CssClass="price"></ItemStyle> </asp:BoundField> <asp:TemplateField HeaderText="ProductID"> <ItemTemplate> <asp:Label ID="lblID" runat="server" Text='<%# Eval("ProductID") %>'></asp:Label> </ItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="ProductName"> <ItemTemplate> <asp:Label ID="lblName" runat="server" Text='<%# Eval("ProductName") %>'></asp:Label> </ItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="Summary"> <ItemTemplate> <asp:Label ID="lblSum" runat="server" Text='<%# Eval("Summary") %>'></asp:Label> </ItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="picPath"> <ItemTemplate> <asp:Label ID="lblPic" runat="server" Text='<%# Eval("picPath") %>' ></asp:Label> </ItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText = "quantity"> <ItemTemplate> <asp:TextBox ID="lblquantity" runat="server" ></asp:TextBox> </ItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText = "Total"> <ItemTemplate> <asp:Label ID="lblTotal" runat="server" ></asp:Label> </ItemTemplate> </asp:TemplateField> </Columns> </asp:GridView> All the information is populated from the session of the privious page, beside this textbox which doesnt comes from anywhere, its a quantity textbox which the user should enter. and i want it to have a defalt value of "1". I dont actually know how to insert into a textbox which is in the gridview. please help me. thanx

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  • Can I set a PHP class property from an existing variable?

    - by jasondavis
    I am trying to figure out how I want to handle settings in my PHP app. I have pretty much decide that I would like to use a Confg class file so it will be autoloaded and flexible in the future. Below is some stuff I was playing with. I know you cannot set a variable to popluate a Constant so I then try to use a public static property. Why can I not set public static $ip = $_SERVER['REMOTE_ADDR']; ?? <?php // config.class.php class Config { const URL = 'http://www.foo.com'; const DB_User = 'dbname'; public static $test = 'test string'; public static $ip = $_SERVER['REMOTE_ADDR']; } /////////////////////////////////////////////////////// //index.php // works echo Config::URL; // works echo Config::$test; // DOES NOT WORK echo Config::$ip; ?>

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  • C++ new line not translating

    - by m3n
    First off, I'm a complete beginner at C++. I'm coding something using an API, and would like to pass text containing new lines to it, and have it print out the new lines at the other end. If I hardcode whatever I want it to print out, like so printInApp("Hello\nWorld"); it does come out as separate lines in the other end, but if I retrieve the text from the app using a method that returns a const char then pass it straight to printInApp (which takes const char as argument), it comes out as a single line. Why's this and how would I go about to fix it?

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  • C++ vs. C++/CLI: Const qualification of virtual function parameters

    - by James McNellis
    [All of the following was tested using Visual Studio 2008 SP1] In C++, const qualification of parameter types does not affect the type of a function (8.3.5/3: "Any cv-qualifier modifying a parameter type is deleted") So, for example, in the following class hierarchy, Derived::Foo overrides Base::Foo: struct Base { virtual void Foo(const int i) { } }; struct Derived : Base { virtual void Foo(int i) { } }; Consider a similar hierarchy in C++/CLI: ref class Base abstract { public: virtual void Foo(const int) = 0; }; ref class Derived : public Base { public: virtual void Foo(int i) override { } }; If I then create an instance of Derived: int main(array<System::String ^> ^args) { Derived^ d = gcnew Derived; } it compiles without errors or warnings. When I run it, it throws the following exception and then terminates: An unhandled exception of type 'System.TypeLoadException' occurred in ClrVirtualTest.exe Additional information: Method 'Foo' in type 'Derived'...does not have an implementation. That exception seems to indicate that the const qualification of the parameter does affect the type of the function in C++/CLI (or, at least it affects overriding in some way). However, if I comment out the line containing the definition of Derived::Foo, the compiler reports the following error (on the line in main where the instance of Derived is instantiated): error C2259: 'Derived': cannot instantiate abstract class If I add the const qualifier to the parameter of Derived::Foo or remove the const qualifier from the parameter of Base::Foo, it compiles and runs with no errors. I would think that if the const qualification of the parameter affects the type of the function, I should get this error if the const qualification of the parameter in the derived class virtual function does not match the const qualification of the parameter in the base class virtual function. If I change the type of Derived::Foo's parameter from an int to a double, I get the following warning (in addition to the aforementioned error, C2259): warning C4490: 'override': incorrect use of override specifier; 'Derived::Foo' does not match a base ref class method So, my question is, effectively, does the const qualification of function parameters affect the type of the function in C++/CLI? If so, why does this compile and why are there no errors or warnings? If not, why is an exception thrown?

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  • Can I use declare-const to eliminate the forall universal quantifier?

    - by monica
    I have some confusion of using universal quantifier and declare-const without using forall (set-option :mbqi true) (declare-fun f (Int Int) Int) (declare-const a Int) (declare-const b Int) (assert (forall ((x Int)) (>= (f x x) (+ x a)))) I can write like this: (declare-const x Int) (assert (>= (f x x) (+ x a)))) with Z3 will explore all the possible values of type Int in this two cases. So what's the difference? Can I really use the declare-const to eliminate the forall quantifier?

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  • What is the best way using multiple lines of <% %> Tag or <% %> Tag with multiple lines?

    - by Salil
    Sorry if the title is not enough to understand what i am asking about. I am rails developer and i used multiple lines of <% % in my views but now i realized that it's not best practice so i came here and like to you all excellent guys what is the correct way in ROR? For example if i required to something like following <% user =User.all %> <% name= [] %> <% count = 0 %> <% for user in users %> <% name << user.name %> <% count+=1%> <% end %> Can i do it as follows ? <% user =User.all name= [] count = 0 for user in users name << user.name count+=1 end %> I know better way of collecting element from array But above is just example. But my question is, is it possible and if yes which is the correct way?

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  • assign member based on string value

    - by Aperion
    I need start off with code because I am not sure what terminology to use. Lets say I have the following code: class Node { public: void Parse(rapidxml::xml_node<> *node) { for (rapidxml::xml_attribute<> *attr = node->first_attribute(); attr; attr = attr->next_attribute()) { std::stringstream converter; converter << attr->value(); if( !strcmp(attr->name(), "x") ) converter >> x; else if( !strcmp(attr->name(),"y") ) converter >> y; else if( !strcmp(attr->name(), "z") ) converter >> z; } } private: float x; float y; float z; }; What I can't stand is the repetition of if( !strcmp(attr-name(), "x") ) converter x; I feel that this is error prone and monotonous, but I cannot think of another way to map a string value to a member assignment. What are some other approaches one can take to avoid code such as this? The only other possible alternative I could think of was to use a hashmap, but that runs into problems with callbacks This is the best I could up with but it's not as flexible as I'd like: class Node { Node() : x(0.0f), y(0.0f), z(0.0f) { assignmentMap["x"] = &x; assignmentMap["y"] = &y; assignmentMap["z"] = &z; } public: void Parse(rapidxml::xml_node<> *node) { for (rapidxml::xml_attribute<> *attr = node->first_attribute(); attr; attr = attr->next_attribute()) { if( !attr->name() ) continue; std::stringstream converter; converter << attr->value(); converter >> *assignmentMap[attr->name()]; } } private: float x; float y; float z; std::map<std::string, float*> assignmentMap; };

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  • Erroneous/Incorrect C2248 error using Visual Studio 2010

    - by Dylan Bourque
    I'm seeing what I believe to be an erroneous/incorrect compiler error using the Visual Studio 2010 compiler. I'm in the process of up-porting our codebase from Visual Studio 2005 and I ran across a construct that was building correctly before but now generates a C2248 compiler error. Obviously, the code snippet below has been generic-ized, but it is a compilable example of the scenario. The ObjectPtr<T> C++ template comes from our codebase and is the source of the error in question. What appears to be happening is that the compiler is generating a call to the copy constructor for ObjectPtr<T> when it shouldn't (see my comment block in the SomeContainer::Foo() method below). For this code construct, there is a public cast operator for SomeUsefulData * on ObjectPtr<SomeUsefulData> but it is not being chosen inside the true expression if the ?: operator. Instead, I get the two errors in the block quote below. Based on my knowledge of C++, this code should compile. Has anyone else seen this behavior? If not, can someone point me to a clarification of the compiler resolution rules that would explain why it's attempting to generate a copy of the object in this case? Thanks in advance, Dylan Bourque Visual Studio build output: c:\projects\objectptrtest\objectptrtest.cpp(177): error C2248: 'ObjectPtr::ObjectPtr' : cannot access private member declared in class 'ObjectPtr' with [ T=SomeUsefulData ] c:\projects\objectptrtest\objectptrtest.cpp(25) : see declaration of 'ObjectPtr::ObjectPtr' with [ T=SomeUsefulData ] c:\projects\objectptrtest\objectptrtest.cpp(177): error C2248: 'ObjectPtr::ObjectPtr' : cannot access private member declared in class 'ObjectPtr' with [ T=SomeUsefulData ] c:\projects\objectptrtest\objectptrtest.cpp(25) : see declaration of 'ObjectPtr::ObjectPtr' with [ T=SomeUsefulData ] Below is a minimal, compilable example of the scenario: #include <stdio.h> #include <tchar.h> template<class T> class ObjectPtr { public: ObjectPtr<T> (T* pObj = NULL, bool bShared = false) : m_pObject(pObj), m_bObjectShared(bShared) {} ~ObjectPtr<T> () { Detach(); } private: // private, unimplemented copy constructor and assignment operator // to guarantee that ObjectPtr<T> objects are not copied ObjectPtr<T> (const ObjectPtr<T>&); ObjectPtr<T>& operator = (const ObjectPtr<T>&); public: T * GetObject () { return m_pObject; } const T * GetObject () const { return m_pObject; } bool HasObject () const { return (GetObject()!=NULL); } bool IsObjectShared () const { return m_bObjectShared; } void ObjectShared (bool bShared) { m_bObjectShared = bShared; } bool IsNull () const { return !HasObject(); } void Attach (T* pObj, bool bShared = false) { Detach(); if (pObj != NULL) { m_pObject = pObj; m_bObjectShared = bShared; } } void Detach (T** ppObject = NULL) { if (ppObject != NULL) { *ppObject = m_pObject; m_pObject = NULL; m_bObjectShared = false; } else { if (HasObject()) { if (!IsObjectShared()) delete m_pObject; m_pObject = NULL; m_bObjectShared = false; } } } void Detach (bool bDeleteIfNotShared) { if (HasObject()) { if (bDeleteIfNotShared && !IsObjectShared()) delete m_pObject; m_pObject = NULL; m_bObjectShared = false; } } bool IsEqualTo (const T * pOther) const { return (GetObject() == pOther); } public: T * operator -> () { ASSERT(HasObject()); return m_pObject; } const T * operator -> () const { ASSERT(HasObject()); return m_pObject; } T & operator * () { ASSERT(HasObject()); return *m_pObject; } const T & operator * () const { ASSERT(HasObject()); return (const C &)(*m_pObject); } operator T * () { return m_pObject; } operator const T * () const { return m_pObject; } operator bool() const { return (m_pObject!=NULL); } ObjectPtr<T>& operator = (T * pObj) { Attach(pObj, false); return *this; } bool operator == (const T * pOther) const { return IsEqualTo(pOther); } bool operator == (T * pOther) const { return IsEqualTo(pOther); } bool operator != (const T * pOther) const { return !IsEqualTo(pOther); } bool operator != (T * pOther) const { return !IsEqualTo(pOther); } bool operator == (const ObjectPtr<T>& other) const { return IsEqualTo(other.GetObject()); } bool operator != (const ObjectPtr<T>& other) const { return !IsEqualTo(other.GetObject()); } bool operator == (int pv) const { return (pv==NULL)? IsNull() : (LPVOID(m_pObject)==LPVOID(pv)); } bool operator != (int pv) const { return !(*this == pv); } private: T * m_pObject; bool m_bObjectShared; }; // Some concrete type that holds useful data class SomeUsefulData { public: SomeUsefulData () {} ~SomeUsefulData () {} }; // Some concrete type that holds a heap-allocated instance of // SomeUsefulData class SomeContainer { public: SomeContainer (SomeUsefulData* pUsefulData) { m_pData = pUsefulData; } ~SomeContainer () { // nothing to do here } public: bool EvaluateSomeCondition () { // fake condition check to give us an expression // to use in ?: operator below return true; } SomeUsefulData* Foo () { // this usage of the ?: operator generates a C2248 // error b/c it's attempting to call the copy // constructor on ObjectPtr<T> return EvaluateSomeCondition() ? m_pData : NULL; /**********[ DISCUSSION ]********** The following equivalent constructs compile w/out error and behave correctly: (1) explicit cast to SomeUsefulData* as a comiler hint return EvaluateSomeCondition() ? (SomeUsefulData *)m_pData : NULL; (2) if/else instead of ?: if (EvaluateSomeCondition()) return m_pData; else return NULL; (3) skip the condition check and return m_pData as a SomeUsefulData* directly return m_pData; **********[ END DISCUSSION ]**********/ } private: ObjectPtr<SomeUsefulData> m_pData; }; int _tmain(int argc, _TCHAR* argv[]) { return 0; }

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