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  • Why do memory-managed languages retain the `new` keyword?

    - by Channel72
    The new keyword in languages like Java, Javascript, and C# creates a new instance of a class. This syntax seems to have been inherited from C++, where new is used specifically to allocate a new instance of a class on the heap, and return a pointer to the new instance. In C++, this is not the only way to construct an object. You can also construct an object on the stack, without using new - and in fact, this way of constructing objects is much more common in C++. So, coming from a C++ background, the new keyword in languages like Java, Javascript, and C# seemed natural and obvious to me. Then I started to learn Python, which doesn't have the new keyword. In Python, an instance is constructed simply by calling the constructor, like: f = Foo() At first, this seemed a bit off to me, until it occurred to me that there's no reason for Python to have new, because everything is an object so there's no need to disambiguate between various constructor syntaxes. But then I thought - what's really the point of new in Java? Why should we say Object o = new Object();? Why not just Object o = Object();? In C++ there's definitely a need for new, since we need to distinguish between allocating on the heap and allocating on the stack, but in Java all objects are constructed on the heap, so why even have the new keyword? The same question could be asked for Javascript. In C#, which I'm much less familiar with, I think new may have some purpose in terms of distinguishing between object types and value types, but I'm not sure. Regardless, it seems to me that many languages which came after C++ simply "inherited" the new keyword - without really needing it. It's almost like a vestigial keyword. We don't seem to need it for any reason, and yet it's there. Question: Am I correct about this? Or is there some compelling reason that new needs to be in C++-inspired memory-managed languages like Java, Javascript and C#?

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  • Formatting Keywords to UPPERCASE In Oracle SQL Developer

    - by thatjeffsmith
    I received this question from a customer today, and it took me more than a few minutes to remember where this preference was located in SQL Developer. This tells me that the topic is ripe for blogging How do I go FROM: select * from scott.emp where ename like '%JEFF%' TO SELECT * FROM scott.emp WHERE ename LIKE '%JEFF%' It’s all in the formatting You need to access the formatting preferences under the Tools menu. It takes a bit of navigating to get there, so bear with me: Tools Database SQL Formatter Oracle Formatting Click ‘Edit’ on the profile Other Case change: ‘Keywords Uppercase’ It’s easy to find once you know where to look? You can tell it to leave the case alone, upper everything, upper only the keywords, lower everything. Accessing the Formatter Options We allow separate formatting options for different RDBMS. You need to make sure you’re accessing the ‘Oracle Formatting’ page in the preferences. You can then choose to edit the default options OR you can do what I have done – save the defaults as a new set of options. I’ve called my profile ‘JeffCustom.’ I can now switch back and forth now through different sets of formatting options. You need to hit the ‘Edit’ button to get to the formatting options editor. A good number of people seem to miss this. Select your profile, then hit the ‘Edit’ button

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  • Don't Use "Static" in C#?

    - by Joshiatto
    I submitted an application I wrote to some other architects for code review. One of them almost immediately wrote me back and said "Don't use "static". You can't write automated tests with static classes and methods. "Static" is to be avoided." I checked and fully 1/4 of my classes are marked "static". I use static when I am not going to create an instance of a class because the class is a single global class used throughout the code. He went on to mention something involving mocking, IOC/DI techniques that can't be used with static code. He says it is unfortunate when 3rd party libraries are static because of their un-testability. Is this other architect correct? update: here is an example: APIManager - this class keeps dictionaries of 3rd party APIs I am calling along with the next allowed time. It enforces API usage limits that a lot of 3rd parties have in their terms of service. I use it anywhere I am calling a 3rd party service by calling Thread.Sleep(APIManager.GetWait("ProviderXYZ")); before making the call. Everything in here is thread safe and it works great with the TPL in C#.

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  • Table and Column names causing problems

    - by craig
    I have an issue when the T4 linq templates generate the classes for my MySql db using subsonic 3. It looks like one of our table names "operator" is causing problems in the Context.cs generated class. In the following line of code in Context.cs Visual Studio sees <operator> as a c# operator and generates a compilation error of "Type expected" public Query<operator> operators { get; set; } Is there anyway I can work around this without having to rename my database table and column names? For example hard coding something in Settings.ttinclude to use or map different names to specific db tables and columns?

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  • What is the best signature for overloaded arithmetic operators in C++?

    - by JohnMcG
    I had assumed that the canonical form for operator+, assuming the existence of an overloaded operator+= member function, was like this: const T operator+(const T& lhs, const T& rhs) { return T(lhs) +=rhs; } But it was pointed out to me that this would also work: const T operator+ (T lhs, const T& rhs) { return lhs+=rhs; } In essence, this form transfers creation of the temporary from the body of the implementation to the function call. It seems a little awkward to have different types for the two parameters, but is there anything wrong with the second form? Is there a reason to prefer one over the other?

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  • C++ type-checking at compile-time

    - by Masterofpsi
    Hi, all. I'm pretty new to C++, and I'm writing a small library (mostly for my own projects) in C++. In the process of designing a type hierarchy, I've run into the problem of defining the assignment operator. I've taken the basic approach that was eventually reached in this article, which is that for every class MyClass in a hierarchy derived from a class Base you define two assignment operators like so: class MyClass: public Base { public: MyClass& operator =(MyClass const& rhs); virtual MyClass& operator =(Base const& rhs); }; // automatically gets defined, so we make it call the virtual function below MyClass& MyClass::operator =(MyClass const& rhs); { return (*this = static_cast<Base const&>(rhs)); } MyClass& MyClass::operator =(Base const& rhs); { assert(typeid(rhs) == typeid(*this)); // assigning to different types is a logical error MyClass const& casted_rhs = dynamic_cast<MyClass const&>(rhs); try { // allocate new variables Base::operator =(rhs); } catch(...) { // delete the allocated variables throw; } // assign to member variables } The part I'm concerned with is the assertion for type equality. Since I'm writing a library, where assertions will presumably be compiled out of the final result, this has led me to go with a scheme that looks more like this: class MyClass: public Base { public: operator =(MyClass const& rhs); // etc virtual inline MyClass& operator =(Base const& rhs) { assert(typeid(rhs) == typeid(*this)); return this->set(static_cast<Base const&>(rhs)); } private: MyClass& set(Base const& rhs); // same basic thing }; But I've been wondering if I could check the types at compile-time. I looked into Boost.TypeTraits, and I came close by doing BOOST_MPL_ASSERT((boost::is_same<BOOST_TYPEOF(*this), BOOST_TYPEOF(rhs)>));, but since rhs is declared as a reference to the parent class and not the derived class, it choked. Now that I think about it, my reasoning seems silly -- I was hoping that since the function was inline, it would be able to check the actual parameters themselves, but of course the preprocessor always gets run before the compiler. But I was wondering if anyone knew of any other way I could enforce this kind of check at compile-time.

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  • templates and casting operators

    - by Jonathan Swinney
    This code compiles in CodeGear 2009 and Visual Studio 2010 but not gcc. Why? class Foo { public: operator int() const; template <typename T> T get() const { return this->operator T(); } }; Foo::operator int() const { return 5; } The error message is: test.cpp: In member function `T Foo::get() const': test.cpp:6: error: 'const class Foo' has no member named 'operator T'

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  • How do I go about overloading C++ operators to allow for chaining?

    - by fneep
    I, like so many programmers before me, am tearing my hair out writing the right-of-passage-matrix-class-in-C++. I have never done very serious operator overloading and this is causing issues. Essentially, by stepping through This is what I call to cause the problems. cMatrix Kev = CT::cMatrix::GetUnitMatrix(4, true); Kev *= 4.0f; cMatrix Baz = Kev; Kev = Kev+Baz; //HERE! What seems to be happening according to the debugger is that Kev and Baz are added but then the value is lost and when it comes to reassigning to Kev, the memory is just its default dodgy values. How do I overload my operators to allow for this statement? My (stripped down) code is below. //header class cMatrix { private: float* _internal; UInt32 _r; UInt32 _c; bool _zeroindexed; //fast, assumes zero index, no safety checks float cMatrix::_getelement(UInt32 r, UInt32 c) { return _internal[(r*this->_c)+c]; } void cMatrix::_setelement(UInt32 r, UInt32 c, float Value) { _internal[(r*this->_c)+c] = Value; } public: cMatrix(UInt32 r, UInt32 c, bool IsZeroIndexed); cMatrix( cMatrix& m); ~cMatrix(void); //operators cMatrix& operator + (cMatrix m); cMatrix& operator += (cMatrix m); cMatrix& operator = (const cMatrix &m); }; //stripped source file cMatrix::cMatrix(cMatrix& m) { _r = m._r; _c = m._c; _zeroindexed = m._zeroindexed; _internal = new float[_r*_c]; UInt32 size = GetElementCount(); for (UInt32 i = 0; i < size; i++) { _internal[i] = m._internal[i]; } } cMatrix::~cMatrix(void) { delete[] _internal; } cMatrix& cMatrix::operator+(cMatrix m) { return cMatrix(*this) += m; } cMatrix& cMatrix::operator*(float f) { return cMatrix(*this) *= f; } cMatrix& cMatrix::operator*=(float f) { UInt32 size = GetElementCount(); for (UInt32 i = 0; i < size; i++) { _internal[i] *= f; } return *this; } cMatrix& cMatrix::operator+=(cMatrix m) { if (_c != m._c || _r != m._r) { throw new cCTException("Cannot add two matrix classes of different sizes."); } if (!(_zeroindexed && m._zeroindexed)) { throw new cCTException("Zero-Indexed mismatch."); } for (UInt32 row = 0; row < _r; row++) { for (UInt32 column = 0; column < _c; column++) { float Current = _getelement(row, column) + m._getelement(row, column); _setelement(row, column, Current); } } return *this; } cMatrix& cMatrix::operator=(const cMatrix &m) { if (this != &m) { _r = m._r; _c = m._c; _zeroindexed = m._zeroindexed; delete[] _internal; _internal = new float[_r*_c]; UInt32 size = GetElementCount(); for (UInt32 i = 0; i < size; i++) { _internal[i] = m._internal[i]; } } return *this; }

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  • Overloading stream insertion without violating information hiding?

    - by Chris
    I'm using yaml-cpp for a project. I want to overload the << and >> operators for some classes, but I'm having an issue grappling with how to "properly" do this. Take the Note class, for example. It's fairly boring: class Note { public: // constructors Note( void ); ~Note( void ); // public accessor methods void number( const unsigned long& number ) { _number = number; } unsigned long number( void ) const { return _number; } void author( const unsigned long& author ) { _author = author; } unsigned long author( void ) const { return _author; } void subject( const std::string& subject ) { _subject = subject; } std::string subject( void ) const { return _subject; } void body( const std::string& body ) { _body = body; } std::string body( void ) const { return _body; } private: unsigned long _number; unsigned long _author; std::string _subject; std::string _body; }; The << operator is easy sauce. In the .h: YAML::Emitter& operator << ( YAML::Emitter& out, const Note& v ); And in the .cpp: YAML::Emitter& operator << ( YAML::Emitter& out, const Note& v ) { out << v.number() << v.author() << v.subject() << v.body(); return out; } No sweat. Then I go to declare the >> operator. In the .h: void operator >> ( const YAML::Node& node, Note& note ); But in the .cpp I get: void operator >> ( const YAML::Node& node, Note& note ) { node[0] >> ? node[1] >> ? node[2] >> ? node[3] >> ? return; } If I write things like node[0] >> v._number; then I would need to change the CV-qualifier to make all of the Note fields public (which defeats everything I was taught (by professors, books, and experience))) about data hiding. I feel like doing node[0] >> temp0; v.number( temp0 ); all over the place is not only tedious, error-prone, and ugly, but rather wasteful (what with the extra copies). Then I got wise: I attempted to move these two operators into the Note class itself, and declare them as friends, but the compiler (GCC 4.4) didn't like that: src/note.h:44: error: ‘YAML::Emitter& Note::operator<<(YAML::Emitter&, const Note&)’ must take exactly one argument src/note.h:45: error: ‘void Note::operator(const YAML::Node&, Note&)’ must take exactly one argument Question: How do I "properly" overload the >> operator for a class Without violating the information hiding principle? Without excessive copying?

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  • Overloading '-' for array subtraction

    - by Chris Wilson
    I am attempting to subtract two int arrays, stored as class members, using an overloaded - operator, but I'm getting some peculiar output when I run tests. The overload definition is Number& Number :: operator-(const Number& NumberObject) { for (int count = 0; count < NumberSize; count ++) { Value[count] -= NumberObject.Value[count]; } return *this; } Whenever I run tests on this, NumberObject.Value[count] always seems to be returning a zero value. Can anyone see where I'm going wrong with this? The line in main() where this subtraction is being carried out is cout << "The difference is: " << ArrayOfNumbers[0] - ArrayOfNumbers[1] << endl; ArrayOfNumbers contains two Number objects. The class declaration is #include <iostream> using namespace std; class Number { private: int Value[50]; int NumberSize; public: Number(); // Default constructor Number(const Number&); // Copy constructor Number(int, int); // Non-default constructor void SetMemberValues(int, int); // Manually set member values int GetNumberSize() const; // Return NumberSize member int GetValue() const; // Return Value[] member Number& operator-=(const Number&); }; inline Number operator-(Number Lhs, const Number& Rhs); ostream& operator<<(ostream&, const Number&); The full class definition is as follows: #include <iostream> #include "../headers/number.h" using namespace std; // Default constructor Number :: Number() {} // Copy constructor Number :: Number(const Number& NumberObject) { int Temp[NumberSize]; NumberSize = NumberObject.GetNumberSize(); for (int count = 0; count < NumberObject.GetNumberSize(); count ++) { Temp[count] = Value[count] - NumberObject.GetValue(); } } // Manually set member values void Number :: SetMemberValues(int NewNumberValue, int NewNumberSize) { NumberSize = NewNumberSize; for (int count = NewNumberSize - 1; count >= 0; count --) { Value[count] = NewNumberValue % 10; NewNumberValue = NewNumberValue / 10; } } // Non-default constructor Number :: Number(int NumberValue, int NewNumberSize) { NumberSize = NewNumberSize; for (int count = NewNumberSize - 1; count >= 0; count --) { Value[count] = NumberValue % 10; NumberValue = NumberValue / 10; } } // Return the NumberSize member int Number :: GetNumberSize() const { return NumberSize; } // Return the Value[] member int Number :: GetValue() const { int ResultSoFar; for (int count2 = 0; count2 < NumberSize; count2 ++) { ResultSoFar = ResultSoFar * 10 + Value[count2]; } return ResultSoFar; } Number& operator-=(const Number& Rhs) { for (int count = 0; count < NumberSize; count ++) { Value[count] -= Rhs.Value[count]; } return *this; } inline Number operator-(Number Lhs, const Number& Rhs) { Lhs -= Rhs; return Lhs; } // Overloaded output operator ostream& operator<<(ostream& OutputStream, const Number& NumberObject) { OutputStream << NumberObject.GetValue(); return OutputStream; }

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  • operator+ overload returning object causing memory leaks, C++

    - by lampshade
    The problem i think is with returing an object when i overload the + operator. I tried returning a reference to the object, but doing so does not fix the memory leak. I can comment out the two statements: dObj = dObj + dObj2; and cObj = cObj + cObj2; to free the program of memory leaks. Somehow, the problem is with returning an object after overloading the + operator. #include <iostream> #include <vld.h> using namespace std; class Animal { public : Animal() {}; virtual void eat() = 0 {}; virtual void walk() = 0 {}; }; class Dog : public Animal { public : Dog(const char * name, const char * gender, int age); Dog() : name(NULL), gender(NULL), age(0) {}; virtual ~Dog(); Dog operator+(const Dog &dObj); private : char * name; char * gender; int age; }; class MyClass { public : MyClass() : action(NULL) {}; void setInstance(Animal &newInstance); void doSomething(); private : Animal * action; }; Dog::Dog(const char * name, const char * gender, int age) : // allocating here, for data passed in ctor name(new char[strlen(name)+1]), gender(new char[strlen(gender)+1]), age(age) { if (name) { size_t length = strlen(name) +1; strcpy_s(this->name, length, name); } else name = NULL; if (gender) { size_t length = strlen(gender) +1; strcpy_s(this->gender, length, gender); } else gender = NULL; if (age) { this->age = age; } } Dog::~Dog() { delete name; delete gender; age = 0; } Dog Dog::operator+(const Dog &dObj) { Dog d; d.age = age + dObj.age; return d; } void MyClass::setInstance(Animal &newInstance) { action = &newInstance; } void MyClass::doSomething() { action->walk(); action->eat(); } int main() { MyClass mObj; Dog dObj("Scruffy", "Male", 4); // passing data into ctor Dog dObj2("Scooby", "Male", 6); mObj.setInstance(dObj); // set the instance specific to the object. mObj.doSomething(); // something happens based on which object is passed in dObj = dObj + dObj2; // invoke the operator+ return 0; }

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  • What is the ISO C++ way to directly define a conversion function to reference to array?

    - by ben
    According to the standard, a conversion function has a function-id operator conversion-type-id, which would look like, say, operator char(&)[4] I believe. But I cannot figure out where to put the function parameter list. gcc does not accept either of operator char(&())[4] or operator char(&)[4]() or anything I can think of. Now, gcc seems to accept (&operator char ())[4] but clang does not, and I am inclined to not either, since it does not seem to fit the grammar as I understand it. I do not want to use a typedef because I want to avoid polluting the namespace with it.

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  • How do I indicate that a class doesn't support certain operators?

    - by romeovs
    I'm writing a class that represents an ordinal scale, but has no logical zero-point (eg time). This scale should permit addition and substraction (operator+, operator+=, ...) but not multiplication. Yet, I always felt it to be a good practice that when one overloads one operator of a certain group (in this case the math operators), one should also overload all the others that belong to that group. In this case that would mean I should need to overload the multiplication and division operators also, because if a user can use A+B he would probable expect to be able the other operators. Is there a method that I can use to throw an error for this at compiler time? The easiest method would be just no to overload the operators operator*, ... yet it would seem appropriate to add a bit more explaination than operator* is not know for class "time". Or is this something that I really should not care about (RTFM user)?

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  • Script throwing unexpected operator when using mysqldump

    - by Astron
    A portion of a script I use to backup MySQL databases has stopped working correctly after upgrading a Debian box to 6.0 Squeeze. I have tested the backup code via CLI and it works fine. I believe it is in the selection of the databases before the backup occurs, possibly something to do with the $skipdb variable. If there is a better way to perform the function then I'm will to try something new. Any insight would be greatly appreciated. $ sudo ./script.sh [: 138: information_schema: unexpected operator [: 138: -1: unexpected operator [: 138: mysql: unexpected operator [: 138: -1: unexpected operator Using bash -x script here is one of the iterations: + for db in '$DBS' + skipdb=-1 + '[' test '!=' '' ']' + for i in '$IGGY' + '[' mysql == test ']' + : + '[' -1 == -1 ']' ++ /bin/date +%F + FILE=/backups/hostname.2011-03-20.mysql.mysql.tar.gz + '[' no = yes ']' + /usr/bin/mysqldump --single-transaction -u root -h localhost '-ppassword' mysql + /bin/tar -czvf /backups/hostname.2011-03-20.mysql.mysql.tar.gz mysql.sql mysql.sql + rm -f mysql.sql Here is the code. if [ $MYSQL_UP = "yes" ]; then echo "MySQL DUMP" >> /tmp/update.log echo "--------------------------------" >> /tmp/update.log DBS="$($MYSQL -u $MyUSER -h $MyHOST -p"$MyPASS" -Bse 'show databases')" for db in $DBS do skipdb=-1 if [ "$IGGY" != "" ] ; then for i in $IGGY do [ "$db" == "$i" ] && skipdb=1 || : done fi if [ "$skipdb" == "-1" ] ; then FILE="$DEST$HOST.`$DATE +"%F"`.$db.mysql.tar.gz" if [ $ENCRYPT = "yes" ]; then $MYSQLDUMP -u $MyUSER -h $MyHOST -p"$MyPASS" $db > $db.sql && $TAR -czvf - $db.sql | $OPENSSL enc -aes-256-cbc -salt -out $FILE.enc -k $ENC_PASS && rm -f $db.sql else $MYSQLDUMP --single-transaction -u $MyUSER -h $MyHOST -p"$MyPASS" $db > $db.sql && $TAR -czvf $FILE $db.sql && rm -f $db.sql fi fi done fi

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  • Guru of the Week 2 no match for the operator==

    - by Adam
    From Guru of the Week 2. We have the function: string FindAddr(const list<Employee> l, string name) { for( list<Employee>::const_iterator i = l.begin(); i != l.end(); i++) { if( *i == name ) // here will be compilation error { return (*i).addr; } } return ""; } I added dummy Employee class to that: class Employee { string n; public: string addr; Employee(string name) : n(name) {} Employee() {} string name() const { return n; } operator string() { return n; } }; And got compilation error: error: no match for ‘operator==’ in ‘i.std::_List_iterator<_Tp>::operator* [with _Tp = Employee]() == name’ It works only if add operator== to Employee. But, Herb Sutter wrote that: The Employee class isn't shown, but for this to work it must either have a conversion to string or a conversion ctor taking a string. But Employee has a conversion function and conversion constructor as well. GCC version 4.4.3. Compiled normally, g++ file.cpp without any flags. There should be implicit conversion and it should work, why it doesn't?

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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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