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  • operator << : std::cout << i << (i << 1);

    - by Oops
    Hi, I use the stream operator << and the bit shifting operator << in one line. I am a bit confused, why does code A) not produce the same output than code B)? A) int i = 4; std::cout << i << " " << (i << 1) << std::endl; //4 8 B) myint m = 4; std::cout << m << " " << (m << 1) << std::endl; //8 8 class myint: class myint { int i; public: myint(int ii) { i = ii; } inline myint operator <<(int n){ i = i << n; return *this; } inline operator int(){ return i; } }; thanks in advance Oops

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  • Custom types as key for a map - C++

    - by Appu
    I am trying to assign a custom type as a key for std::map. Here is the type which I am using as key. struct Foo { Foo(std::string s) : foo_value(s){} bool operator<(const Foo& foo1) { return foo_value < foo1.foo_value; } bool operator>(const Foo& foo1) { return foo_value > foo1.foo_value; } std::string foo_value; }; When used with std::map, I am getting the following error. error C2678: binary '<' : no operator found which takes a left-hand operand of type 'const Foo' (or there is no acceptable conversion) c:\program files\microsoft visual studio 8\vc\include\functional 143 If I change the struct like the below, everything worked. struct Foo { Foo(std::string s) : foo_value(s) {} friend bool operator<(const Foo& foo,const Foo& foo1) { return foo.foo_value < foo1.foo_value; } friend bool operator>(const Foo& foo,const Foo& foo1) { return foo.foo_value > foo1.foo_value; } std::string foo_value; }; Nothing changed except making the operator overloads as friend. I am wondering why my first code is not working? Any thoughts?

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  • defining < operator for map of list iterators

    - by Adrian
    I'd like to use iterators from an STL list as keys in a map. For example: using namespace std; list<int> l; map<list<int>::const_iterator, int> t; int main(int argv, char * argc) { l.push_back(1); t[l.begin()] = 5; } However, list iterators do not have a comparison operator defined (in contrast to random access iterators), so compiling the above code results in an error: /usr/include/c++/4.2.1/bits/stl_function.h:227: error: no match for ‘operator<’ in ‘__x < __y’ If the list is changed to a vector, a map of vector const_iterators compiles fine. What is the appropriate way to define the operator < for list::const_iterator?

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  • Allow member to be const while still supporting operator= on the class

    - by LeopardSkinPillBoxHat
    I have several members in my class which are const and can therefore only be initialised via the initialiser list like so: class MyItemT { public: MyItemT(const MyPacketT& aMyPacket, const MyInfoT& aMyInfo) : mMyPacket(aMyPacket), mMyInfo(aMyInfo) { } private: const MyPacketT mMyPacket; const MyInfoT mMyInfo; }; My class can be used in some of our internally defined container classes (e.g. vectors), and these containers require that operator= is defined in the class. Of course, my operator= needs to do something like this: MyItemT& MyItemT::operator=(const MyItemT& other) { mMyPacket = other.mPacket; mMyInfo = other.mMyInfo; return *this; } which of course doesn't work because mMyPacket and mMyInfo are const members. Other than making these members non-const (which I don't want to do), any ideas about how I could fix this?

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  • Concatenation Operator

    - by Chaitanya
    This might be a silly question but it struck me, and here i ask. <?php $x="Hi"; $y=" There"; $z = $x.$y; $a = "$x$y"; echo "$z"."<br />"."$a"; ?> $z uses the traditional concatenation operator provided by php and concatenates, conversely $a doesn't, My questions: by not using the concatenation operator, does it effect the performance? If it doesn't why at all have the concatenation operator. Why have 2 modes of implementation when one does the work?

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  • Concatenation Operator - PHP

    - by Chaitanya
    This might be a silly question but it struck me, and here i ask. <?php $x="Hi"; $y=" There"; $z = $x.$y; $a = "$x$y"; echo "$z"."<br />"."$a"; ?> $z uses the traditional concatenation operator provided by php and concatenates, conversely $a doesn't, My questions: a. by not using the concatenation operator, does it effect the performance? b. If it doesn't why at all have the concatenation operator. c. Why have 2 modes of implementation when one does the work?

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  • Understanding pattern matching with cons operator

    - by Mathias
    In "Programming F#" I came across a pattern-matching like this one (I simplified a bit): let rec len list = match list with | [] -> 0 | [_] -> 1 | head :: tail -> 1 + len tail;; Practically, I understand that the last match recognizes the head and tail of the list. Conceptually, I don't get why it works. As far as I understand, :: is the cons operator, which appends a value in head position of a list, but it doesn't look to me like it is being used as an operator here. Should I understand this as a "special syntax" for lists, where :: is interpreted as an operator or a "match pattern" depending on context? Or can the same idea be extended for types other than lists, with other operators?

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  • Should I make OR operator to return const reference or just reference

    - by Yan Cheng CHEOK
    class error_code { public: error_code() : hi(0), lo(0) {} error_code(__int64 lo) : hi(0), lo(lo) {} error_code(__int64 hi, __int64 lo) : hi(hi), lo(lo) {} error_code& operator|=(const error_code &e) { this->hi |= e.hi; this->lo |= e.lo; return *this; } __int64 hi; __int64 lo; }; error_code operator|(const error_code& e0, const error_code& e1) { return error_code(e0.hi | e1.hi, e0.lo | e1.lo); } int main() { error_code e0(1); error_code e1(2); e0 |= e1; } I was wondering, whether I should make operator|= to return a const error_code& or error_code& ?

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  • Does dynamic_cast work inside overloaded operator delete ?

    - by iammilind
    I came across this: struct Base { void* operator new (size_t); void operator delete (void*); virtual ~Base () {} // <--- polymorphic }; struct Derived : Base {}; void Base::operator delete (void *p) { Base *pB = static_cast<Base*>(p); if(dynamic_cast<Derived*>(pB) != 0) { /* ... NOT reaching here ? ... */ } free(p); } Now if we do, Base *p = new Derived; delete p; Surprisingly, the condition inside the Base::delete is not satisfied Am I doing anything wrong ? Or casting from void* looses the information of Derived* ?

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  • Is c++ explicit conversion really that bad?

    - by LoudNPossiblyRight
    My knowledge in c++ at this point is more academic than anything else and in all my reading thus far, the use of explicit conversion with named casts (const_cast, static_cast, reinterpret_cast, dynamic_cast) has come with a big warning label (and it's easy to see why) that pretty much implies explicit conversion is symptomatic of bad design and should only be used as a last resort in desperate circumstances. So i have to ask: Is explicit conversion with named casts really just jury rigging code or is there a more graceful and positive application to this feature? Is there a good example of the latter? Thanks in advance.

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  • (C++) What's the difference between these overloaded operator functions?

    - by cv3000
    What is the difference between these two ways of overloading the != operator below. Which is consider better? Class Test { ...// private: int iTest public: BOOL operator==(const &Test test) const; BOOL operator!=(const &Test test) const; } BOOL operator==(const &Test test) const { return (iTest == test.iTest); } //overload function 1 BOOL Test::operator!=(const &Test test) const { return !operator==(test); } //overload function 2 BOOL Test::operator!=(const &Test test) const { return (iTest != test.iTest); } I've just recently seen function 1's syntax for calling a sibling operator function and wonder if writing it that way provides any benefits.

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  • Why can't we have an immutable version of operator[] for map

    - by Yan Cheng CHEOK
    The following code works fine : std::map<int, int>& m = std::map<int, int>(); int i = m[0]; But not the following code : // error C2678: binary '[' : no operator... const std::map<int, int>& m = std::map<int, int>(); int i = m[0]; Most of the time, I prefer to make most of my stuff to become immutable, due to reason : http://www.javapractices.com/topic/TopicAction.do?Id=29 I look at map source code. It has mapped_type& operator[](const key_type& _Keyval) Is there any reason, why std::map unable to provide const mapped_type& operator[](const key_type& _Keyval) const

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  • Is the "==" operator required to be defined to use std::find

    - by user144182
    Let's say I have: class myClass std::list<myClass> myList where myClass does not define the == operator and only consists of public fields. In both VS2010 and VS2005 the following does not compile: myClass myClassVal = myList.front(); std::find( myList.begin(), myList.end(), myClassVal ) complaining about lack of == operator. I naively assumed it would do a value comparison of the myClass object's public members, but I am almost positive this is not correct. I assume if I define a == operator or perhaps use a functor instead, it will solve the problem. Alternatively, if my list was holding pointers instead of values, the comparison would work. Is this right or should I be doing something else?

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  • Google Adword not working /conversion.js not found

    - by Jed
    I'm currently working on a wordpress site. My task is just to add the conversion script in a thankyou page. I added the script here: http://www.livingedge.co.nz/thanks-for-getting-in-touch/ , unfortunately does not work. It says that a conversion.js was not found. See the attached screenshot: http://screencast.com/t/52ixQUzHKNxZ I added the conversion script on the footer put it in a conditional so that it will load only on the thakyoupage. I'm new to this and can't figure out what would be the possible cause of such problem. I tried adding the script in the header, on the page editor, on a form redirect. Q: What could be the possible cause of this issue?

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  • Entity Framework with SQL Server 2000 (APPLY Operator) issue

    - by How Lun
    Hello, I have a simple Linq query below: var seq = (from n in GetObjects() select n.SomeKey) .Distinct() .Count(); This query works find with SQL Server 2005 and above. But, this start to give headache when I hooked the EF to SQL Server 2000. Because EF is using APPLY operator which only SQL Server 2005 and above can be supported. I do not know why the hell EF is using APPLy operator instead of sub queries. My current work around is: var seq = (from n in GetObjects() select n.SomeKey) .Distinct() .ToList() .Count(); But, I can forsee more problems to come. The above query is just a simple one. Did anyone come across such issue? And how you guys work around it? Or is there a way to force EF not to use APPLY operator? Any help will be very much appreciated. How Lun.

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  • Failed Conversion with VMConverter 4.0.1

    - by montespcs
    Received this error @ 57% on Windows Vista Enterprise SP1 conversion going to a VMWorkstation 6.5 image via network share. FAILED: A general system error occurred: SQL_CANTOPEN: unable to open database file Running installed VMConverter 4.0.1-Build161434. Anyone seen this error yet?

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  • Batch Conversion of PaperPort MAX Files

    - by Matthew
    I've got a library of MAX files from an old Visioneer Scanner that used ScanSoft PaperPort. I don't have the PC that I used to scan them anymore, and I don't have the CD for PaperPort. Does anyone know of a utility I can use to open and convert .MAX files to something more useful like a JPEG? (I'd prefer something that batch converts -- but if I can get a utility that will even allow one conversion, I could probably figure out how to use AutoHotkey or something like that to automate.) Thanks for your help

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  • When is #include <new> library required in C++?

    - by Czarak
    Hi, According to this reference entry for operator new ( http://www.cplusplus.com/reference/std/new/operator%20new/ ) : Global dynamic storage operator functions are special in the standard library: All three versions of operator new are declared in the global namespace, not in the std namespace. The first and second versions are implicitly declared in every translation unit of a C++ program: The header does not need to be included for them to be present. This seems to me to imply that the third version of operator new (placement new) is not implicitly declared in every translation unit of a C++ program and the header <new> does need to be included for it to be present. Is that correct? If so, how is it that using both g++ and MS VC++ Express compilers it seems I can compile code using the third version of new without #include <new> in my source code? Also, the MSDN Standard C++ Library reference entry on operator new gives some example code for the three forms of operator new which contains the #include <new> statement, however the example seems to compile and run just the same for me without this include? // new_op_new.cpp // compile with: /EHsc #include<new> #include<iostream> using namespace std; class MyClass { public: MyClass( ) { cout << "Construction MyClass." << this << endl; }; ~MyClass( ) { imember = 0; cout << "Destructing MyClass." << this << endl; }; int imember; }; int main( ) { // The first form of new delete MyClass* fPtr = new MyClass; delete fPtr; // The second form of new delete char x[sizeof( MyClass )]; MyClass* fPtr2 = new( &x[0] ) MyClass; fPtr2 -> ~MyClass(); cout << "The address of x[0] is : " << ( void* )&x[0] << endl; // The third form of new delete MyClass* fPtr3 = new( nothrow ) MyClass; delete fPtr3; } Could anyone shed some light on this and when and why you might need to #include <new> - maybe some example code that will not compile without #include <new> ? Thanks.

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  • C++ addition overload ambiguity

    - by Nate
    I am coming up against a vexing conundrum in my code base. I can't quite tell why my code generates this error, but (for example) std::string does not. class String { public: String(const char*str); friend String operator+ ( const String& lval, const char *rval ); friend String operator+ ( const char *lval, const String& rval ); String operator+ ( const String& rval ); }; The implementation of these is easy enough to imagine on your own. My driver program contains the following: String result, lval("left side "), rval("of string"); char lv[] = "right side ", rv[] = "of string"; result = lv + rval; printf(result); result = (lval + rv); printf(result); Which generates the following error in gcc 4.1.2: driver.cpp:25: error: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: String.h:22: note: candidate 1: String operator+(const String&, const char*) String.h:24: note: candidate 2: String String::operator+(const String&) So far so good, right? Sadly, my String(const char *str) constructor is so handy to have as an implicit constructor, that using the explicit keyword to solve this would just cause a different pile of problems. Moreover... std::string doesn't have to resort to this, and I can't figure out why. For example, in basic_string.h, they are declared as follows: template<typename _CharT, typename _Traits, typename _Alloc> basic_string<_CharT, _Traits, _Alloc> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, const basic_string<_CharT, _Traits, _Alloc>& __rhs) template<typename _CharT, typename _Traits, typename _Alloc> basic_string<_CharT,_Traits,_Alloc> operator+(const _CharT* __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs); and so on. The basic_string constructor is not declared explicit. How does this not cause the same error I'm getting, and how can I achieve the same behavior??

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  • why there is no power operator in java / c ++?

    - by RanZilber
    While there is such operator - ** in Python , i was wondering why java and c++ havent got one too. It is easy to make one for classes you define in C++ with operator overloading ( and i believe such thing is possible also in java) , but when talking about primitive types such as int, double and so on , you'll have to use library function like Math.power (and usaully have to cast both to double). So - why not define such operator for primitive types ?

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  • Trying to reduce the speed overhead of an almost-but-not-quite-int number class

    - by Fumiyo Eda
    I have implemented a C++ class which behaves very similarly to the standard int type. The difference is that it has an additional concept of "epsilon" which represents some tiny value that is much less than 1, but greater than 0. One way to think of it is as a very wide fixed point number with 32 MSBs (the integer parts), 32 LSBs (the epsilon parts) and a huge sea of zeros in between. The following class works, but introduces a ~2x speed penalty in the overall program. (The program includes code that has nothing to do with this class, so the actual speed penalty of this class is probably much greater than 2x.) I can't paste the code that is using this class, but I can say the following: +, -, +=, <, > and >= are the only heavily used operators. Use of setEpsilon() and getInt() is extremely rare. * is also rare, and does not even need to consider the epsilon values at all. Here is the class: #include <limits> struct int32Uepsilon { typedef int32Uepsilon Self; int32Uepsilon () { _value = 0; _eps = 0; } int32Uepsilon (const int &i) { _value = i; _eps = 0; } void setEpsilon() { _eps = 1; } Self operator+(const Self &rhs) const { Self result = *this; result._value += rhs._value; result._eps += rhs._eps; return result; } Self operator-(const Self &rhs) const { Self result = *this; result._value -= rhs._value; result._eps -= rhs._eps; return result; } Self operator-( ) const { Self result = *this; result._value = -result._value; result._eps = -result._eps; return result; } Self operator*(const Self &rhs) const { return this->getInt() * rhs.getInt(); } // XXX: discards epsilon bool operator<(const Self &rhs) const { return (_value < rhs._value) || (_value == rhs._value && _eps < rhs._eps); } bool operator>(const Self &rhs) const { return (_value > rhs._value) || (_value == rhs._value && _eps > rhs._eps); } bool operator>=(const Self &rhs) const { return (_value >= rhs._value) || (_value == rhs._value && _eps >= rhs._eps); } Self &operator+=(const Self &rhs) { this->_value += rhs._value; this->_eps += rhs._eps; return *this; } Self &operator-=(const Self &rhs) { this->_value -= rhs._value; this->_eps -= rhs._eps; return *this; } int getInt() const { return(_value); } private: int _value; int _eps; }; namespace std { template<> struct numeric_limits<int32Uepsilon> { static const bool is_signed = true; static int max() { return 2147483647; } } }; The code above works, but it is quite slow. Does anyone have any ideas on how to improve performance? There are a few hints/details I can give that might be helpful: 32 bits are definitely insufficient to hold both _value and _eps. In practice, up to 24 ~ 28 bits of _value are used and up to 20 bits of _eps are used. I could not measure a significant performance difference between using int32_t and int64_t, so memory overhead itself is probably not the problem here. Saturating addition/subtraction on _eps would be cool, but isn't really necessary. Note that the signs of _value and _eps are not necessarily the same! This broke my first attempt at speeding this class up. Inline assembly is no problem, so long as it works with GCC on a Core i7 system running Linux!

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  • Converting a Visual Studio 2003 Web Project to a Visual Studio 2008 Web Application Project

    - by navaneeth
    This walkthrough describes how to convert a Visual Studio .NET 2002 or Visual Studio .NET 2003 Web project to a Visual Studio 2008 Web application project. The Visual Studio 2008 Web application project model is like the Visual Studio 2005 Web application project model. Therefore, the conversion processes are similar. For more information about Web application projects, see ASP.NET Web Application Projects. You can also convert from a Visual Studio .NET Web project to a Visual Studio 2008 Web site project. However, conversion to a Web application project is the approach that is supported, and gives you the convenience of tools to help with the conversion. For example, when you convert to a Visual Studio 2008 Web application project, you can use the Visual Studio Conversion Wizard to automate part of the process. For information about how to convert a Visual Studio .NET Web project to a Visual Studio 2008 Web site, see Common Web Project Conversion Issues and Solutions. There are two parts involved in converting a Visual Studio 2002 or 2003 Web project to a Visual Studio 2008 Web application project. The parts are as follows: Converting the project. You can use the Visual Studio Conversion Wizard for the initial conversion of the project and Web.config files. You can later use the Convert To Web Application command to update the project's files and structure. Upgrading the .NET Framework version of the project. You must upgrade the project's .NET Framework version to either .NET Framework 2.0 SP1 or to .NET Framework 3.5. This .NET Framework version upgrade is required because Visual Studio 2008 cannot target earlier versions of the .NET Framework. You can perform this upgrade during the project conversion, by using the Conversion Wizard. Alternatively, you can upgrade the .NET Framework version after you convert the project.   NoteYou can change a project's .NET Framework version manually. To do so, in Visual Studio open the property pages for the project, click the Application tab, and then select a new version from the Target Framework list. This walkthrough illustrates the following tasks: Opening the Visual Studio .NET project in Visual Studio 2008 and creating a backup of the project files. Upgrading the .NET Framework version that the project targets. Converting the project file and the Web.config file. Converting ASP.NET code files. Testing the converted project. Prerequisites    To complete this walkthrough, you will need: Visual Studio 2008. A Web site project that was created in Visual Studio .NET version 2002 or 2003 that compiles and runs without errors. Converting the Project and Upgrading the .NET Framework Version    To begin, you open the project in Visual Studio 2008, which starts the conversion. It offers you an opportunity to back up the project before converting it. NoteIt is strongly recommended that you back up the project. The conversion works on the original project files, which cannot be recovered if the conversion is not successful.To convert the project and back up the files In Visual Studio 2008, in the File menu, click Open and then click Project. The Open Project dialog box is displayed. Browse to the folder that contains the project or solution file for the Visual Studio .NET project, select the file, and then click Open. NoteMake sure that you open the project by using the Open Project command. If you use the Open Web Site command, the project will be converted to the Web site project format.The Conversion Wizard opens and prompts you to create a backup before converting the project. To create the backup, click Yes. Click Browse, select the folder in which the backup should be created, and then click Next. Click Finish. The backup starts. NoteThere might be significant delays as the Conversion Wizard copies files, with no updates or progress indicated. Wait until the process finishes before you continue.When the conversion finishes, the wizard prompts you to upgrade the targeted version of the .NET Framework for the project. To upgrade to the .NET Framework 3.5, click Yes. To upgrade the project to target the .NET Framework 2.0 SP1, click No. It is recommended that you leave the check box selected that asks whether you want to upgrade all Webs in the solution. If you upgrade to .NET Framework 3.5, the project's Web.config file is modified at the same time as the project file. When the upgrade and conversion have finished, a message is displayed that indicates that you have completed the first step in converting your project. Click OK. The wizard displays status information about the conversion. Click Close. Testing the Converted Project    After the conversion has finished, you can test the project to make sure that it runs. This will also help you identify code in the project that must be updated. To verify that the project runs If you know about changes that are required for the code to run with the new version of the .NET Framework, make those changes. In the Build menu, click Build. Any missing references or other compilation issues in the project are displayed in the Error List window. The most likely issues are missing assembly references or issues with dynamically generated types. In Solution Explorer, right-click the Web page that will be used to launch the application, and then click Set as Start Page. On the Debug menu, click Start Debugging. If debugging is not enabled, the Debugging Not Enabled dialog box is displayed. Select the option to add a Web.config file that has debugging enabled, and then click OK. Verify that the converted project runs as expected. Do not continue with the conversion process until all build and run-time errors are resolved. Converting ASP.NET Code Files    ASP.NET Web page files and user-control files in Visual Studio 2008 that use the code-behind model have an associated designer file. The files that you just converted will have an associated code-behind file, but no designer file. Therefore, the next step is to generate designer files. NoteOnly ASP.NET Web pages and user controls that have their code in a separate code file require a separate designer file. For pages that have inline code and no associated code file, no designer file will be generated.To convert ASP.NET code files In Solution Explorer, right-click the project node, and then click Convert To Web Application. The files are converted. Verify that the converted code files have a code file and a designer file. Build and run the project to verify the results of the conversion.

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