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  • binary operator "<"

    - by md004
    Consider this expression as a "selection" control structure on integer "x": 0 < x < 10, with the intention that the structure returns TRUE if "x" is in the range 1..9. Explain why a compiler should not accept this expression. (In particular, what are the issues regarding the binary operator "<"? Explain how a prefix operator could be introduced so the expression can be successfully processed.

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  • Polynomial operations using operator overloading

    - by Vlad
    I'm trying to use operator overloading to define the basic operations (+,-,*,/) for my polynomial class but when i run the program it crashes and my computer frozes. Update3 Ok i successfully done the first two operations(+,-). Now at multiplication, after multiplying each term of the first polynomial with each of the second i want to sort the poly list descending and then if there are more than one term with the same power to merge them in only one term, but for some reason it doesn't compile because of the sort function which doesn't work. Here's what I got: polinom operator*(const polinom& P) const { polinom Result; constIter i, j, lastItem = Result.poly.end(); Iter it1, it2; int nr_matches; for (i = poly.begin() ; i != poly.end(); i++) { for (j = P.poly.begin(); j != P.poly.end(); j++) Result.insert(i->coef * j->coef, i->pow + j->pow); } sort(Result.poly.begin(), Result.poly.end(), SortDescending()); lastItem--; while (true) { nr_matches = 0; for (it1 = Result.poly.begin(); it < lastItem; it1++) { for (it2 = it1 + 1;; it2 <= lastItem; it2++){ if (it2->pow == it1->pow) { it1->coef += it2->coef; nr_matches++; } } Result.poly.erase(it1 + 1, it1 + (nr_matches + 1)); } return Result; } Also here's SortDescending: struct SortDescending { bool operator()(const term& t1, const term& t2) { return t2.pow < t1.pow; } }; What did i do wrong? Thanks!

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  • Template operator linker error

    - by Dani
    I have a linker error I've reduced to a simple example. The build output is: debug/main.o: In function main': C:\Users\Dani\Documents\Projects\Test1/main.cpp:5: undefined reference tolog& log::operator<< (char const (&) [6])' collect2: ld returned 1 exit status It looks like the linker ignores the definition in log.cpp. I also cant put the definition in log.h because I include the file alot of times and it complains about redefinitions. main.cpp: #include "log.h" int main() { log() << "hello"; return 0; } log.h: #ifndef LOG_H #define LOG_H class log { public: log(); template<typename T> log &operator <<(T &t); }; #endif // LOG_H log.cpp: #include "log.h" #include <iostream> log::log() { } template<typename T> log &log::operator <<(T &t) { std::cout << t << std::endl; return *this; }

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  • How to make std::vector's operator[] compile doing bounds checking in DEBUG but not in RELEASE

    - by Edison Gustavo Muenz
    I'm using Visual Studio 2008. I'm aware that std::vector has bounds checking with the at() function and has undefined behaviour if you try to access something using the operator [] incorrectly (out of range). I'm curious if it's possible to compile my program with the bounds checking. This way the operator[] would use the at() function and throw a std::out_of_range whenever something is out of bounds. The release mode would be compiled without bounds checking for operator[], so the performance doesn't degrade. I came into thinking about this because I'm migrating an app that was written using Borland C++ to Visual Studio and in a small part of the code I have this (with i=0, j=1): v[i][j]; //v is a std::vector<std::vector<int> > The size of the vector 'v' is [0][1] (so element 0 of the vector has only one element). This is undefined behaviour, I know, but Borland is returning 0 here, VS is crashing. I like the crash better than returning 0, so if I can get more 'crashes' by the std::out_of_range exception being thrown, the migration would be completed faster (so it would expose more bugs that Borland was hiding).

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  • c# "==" operator : compiler behaviour with different structs

    - by Moe Sisko
    Code to illustrate : public struct MyStruct { public int SomeNumber; } public string DoSomethingWithMyStruct(MyStruct s) { if (s == null) return "this can't happen"; else return "ok"; } private string DoSomethingWithDateTime(DateTime s) { if (s == null) return "this can't happen"; // XX else return "ok"; } Now, "DoSomethingWithStruct" fails to compile with : "Operator '==' cannot be applied to operands of type 'MyStruct' and '<null>'". This makes sense, since it doesn't make sense to try a reference comparison with a struct, which is a value type. OTOH, "DoSomethingWithDateTime" compiles, but with compiler warning : "Unreachable code detected" at line marked "XX". Now, I'm assuming that there is no compiler error here, because the DateTime struct overloads the "==" operator. But how does the compiler know that the code is unreachable ? e.g. Does it look inside the code which overloads the "==" operator ? (This is using Visual Studio 2005 in case that makes a difference). Note : I'm more curious than anything about the above. I don't usually try to use "==" on structs and nulls.

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  • Java Newbie can't do simple Math, operator error

    - by elguapo-85
    Trying to do some really basic math here, but my lack of understanding of Java is causing some problems for me. double[][] handProbability = new double[][] {{0,0,0},{0,0,0},{0,0,0}}; double[] handProbabilityTotal = new double[] {0,0,0}; double positivePot = 0; double negativePot = 0; int localAhead = 0; int localTied = 1; int localBehind = 2; //do some stuff that adds values to handProbability and handProbabilityTotal positivePot = (handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0)); negativePot = (handProbability[localAhead][localBehind] + (handProbability[localAhead][localTied] / 2.0) + (handProbability[localTied][localBehind] / 2.0) ) / (handProbabilityTotal[localAhead] + (handProbabilityTotal[localTied] / 2.0)); The last two lines are giving me problems (sorry for their lengthiness). Compiler Errors: src/MyPokerClient/MyPokerClient.java:180: operator / cannot be applied to double[],double positivePot = ( handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0) ); ^ src/MyPokerClient/MyPokerClient.java:180: operator + cannot be applied to double, positivePot = ( handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0) ); ^ src/MyPokerClient/MyPokerClient.java:180: operator / cannot be applied to double, positivePot = ( handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0) ); Not really sure what the problem is. You shouldn't need anything special for basic math, right?

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  • Using overloaded operator== in a generic function

    - by Dimitri C.
    Consider the following code: class CustomClass { public CustomClass(string value) { m_value = value; } public static bool operator==(CustomClass a, CustomClass b) { return a.m_value == b.m_value; } public static bool operator!=(CustomClass a, CustomClass b) { return a.m_value != b.m_value; } public override bool Equals(object o) { return m_value == (o as CustomClass).m_value; } public override int GetHashCode() { return 0; /* not needed */ } string m_value; } class G { public static bool enericFunction1<T>(T a1, T a2) where T : class { return a1.Equals(a2); } public static bool enericFunction2<T>(T a1, T a2) where T : class { return a1==a2; } } Now when I call both generic functions, one succeeds and one fails: var a = new CustomClass("same value"); var b = new CustomClass("same value"); Debug.Assert(G.enericFunction1(a, b)); // Succeeds Debug.Assert(G.enericFunction2(a, b)); // Fails Apparently, G.enericFunction2 executes the default operator== implementation instead of my override. Can anybody explain why this happens?

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  • Trying to overload + operator

    - by FrostyStraw
    I cannot for the life of me understand why this is not working. I am so confused. I have a class Person which has a data member age, and I just want to add two people so that it adds the ages. I don't know why this is so hard, but I'm looking for examples and I feel like everyone does something different, and for some reason NONE of them work. Sometimes the examples I see have two parameters, sometimes they only have one, sometimes the parameters are references to the object, sometimes they're not, sometimes they return an int, sometimes they return a Person object. Like..what is the most normal way to do it? class Person { public: int age; //std::string haircolor = "brown"; //std::string ID = "23432598"; Person(): age(19) {} Person operator+(Person&) { } }; Person operator+(Person &obj1, Person &obj2){ Person sum = obj1; sum += obj2; return sum; } I really feel like overloading a + operator should seriously be the easiest thing in the world except I DON'T KNOW WHAT I AM DOING. I don't know if I'm supposed to create the overload function inside the class, outside, if it makes a difference, why if I do it inside it only allows one parameter, I just honestly don't get it.

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  • Visitor and templated virtual methods

    - by Thomas Matthews
    In a typical implementation of the Visitor pattern, the class must account for all variations (descendants) of the base class. There are many instances where the same method content in the visitor is applied to the different methods. A templated virtual method would be ideal in this case, but for now, this is not allowed. So, can templated methods be used to resolve virtual methods of the parent class? Given (the foundation): struct Visitor_Base; // Forward declaration. struct Base { virtual accept_visitor(Visitor_Base& visitor) = 0; }; // More forward declarations struct Base_Int; struct Base_Long; struct Base_Short; struct Base_UInt; struct Base_ULong; struct Base_UShort; struct Visitor_Base { virtual void operator()(Base_Int& b) = 0; virtual void operator()(Base_Long& b) = 0; virtual void operator()(Base_Short& b) = 0; virtual void operator()(Base_UInt& b) = 0; virtual void operator()(Base_ULong& b) = 0; virtual void operator()(Base_UShort& b) = 0; }; struct Base_Int : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Long : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Short : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UInt : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_ULong : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UShort : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; Now that the foundation is laid, here is where the kicker comes in (templated methods): struct Visitor_Cout : public Visitor { template <class Receiver> void operator() (Receiver& r) { std::cout << "Visitor_Cout method not implemented.\n"; } }; Intentionally, Visitor_Cout does not contain the keyword virtual in the method declaration. All the other attributes of the method signatures match the parent declaration (or perhaps specification). In the big picture, this design allows developers to implement common visitation functionality that differs only by the type of the target object (the object receiving the visit). The implementation above is my suggestion for alerts when the derived visitor implementation hasn't implement an optional method. Is this legal by the C++ specification? (I don't trust when some says that it works with compiler XXX. This is a question against the general language.)

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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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  • explicit copy constructor or implicit parameter by value

    - by R Samuel Klatchko
    I recently read (and unfortunately forgot where), that the best way to write operator= is like this: foo &operator=(foo other) { swap(*this, other); return *this; } instead of this: foo &operator=(const foo &other) { foo copy(other); swap(*this, copy); return *this; } The idea is that if operator= is called with an rvalue, the first version can optimize away construction of a copy. So when called with a rvalue, the first version is faster and when called with an lvalue the two are equivalent. I'm curious as to what other people think about this? Would people avoid the first version because of lack of explicitness? Am I correct that the first version can be better and can never be worse?

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  • Overloading new, delete in C++

    - by user265260
    i came across this line is stroustrup An operator function must either be a member or take at least one argument of a user-defined type (functions redefining the new and delete operators need not). Dont operator new and operator delete take an user defined type as one of their arguments? what does it mean, am i missing something here

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  • C++ Code Clarification Needed..

    - by ke3pup
    Hi guys I'm trying to understand what the code below says: struct compare_pq; struct compare_pq { bool operator() (Events *& a, Events *& b); }; std::priority_queue<Events *, std::vector<Events *>, compare_pq> eventList; i looked at what priority_queue is and how its declared but can't quit understand what compare_pq is doing in the priority_queue eventList. Also what does operator() do since i've never seen *& before and empty operator overloading operator()! any help would be appreciated. Thank you

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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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  • What does the caret operator in Python do?

    - by Fry
    I ran across the caret operator in python today and trying it out, I got the following output: >>> 8^3 11 >>> 8^4 12 >>> 8^1 9 >>> 8^0 8 >>> 7^1 6 >>> 7^2 5 >>> 7^7 0 >>> 7^8 15 >>> 9^1 8 >>> 16^1 17 >>> 15^1 14 >>> It seems to be based on 8, so I'm guessing some sort of byte operation? I can't seem to find much about this searching sites other than it behaves oddly for floats, does anybody have a link to what this operator does or can you explain it here?

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  • Conditional Operator in SQL Where Clause

    - by Marc
    I'm wishing I could do something like the following in SQl Server 2005 (which I know isnt valid) for my where clause. Sometimes @teamID (passed into a stored procedure) will be the value of an existing teamID, otherwise it will always be zero and I want all rows from the Team table. I researched using Case and the operator needs to come before or after the entire statement which prevents me from having a different operator based on the value of @teamid. Any suggestions other than duplicating my select statements. declare @teamid int set @teamid = 0 Select Team.teamID From Team case @teamid when 0 then WHERE Team.teamID > 0 else WHERE Team.teamID = @teamid end

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  • Can operator= may be not a member?

    - by atch
    Having construction in a form: struct Node { Node():left_(nullptr), right_(nullptr) { } int id_; Node* left_; Node* right_; }; I would like to enable syntax: Node parent; Node child; parent.right_ = child; So in order to do so I need: Node& operator=(Node* left, Node right); but I'm getting msg that operator= has to be a member fnc; Is there any way to circumvent this restriction?

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  • Is a switch statement the fastest way to implement operator interpretation in Java

    - by Mordan
    Is a switch statement the fastest way to implement operator interpretation in Java public boolean accept(final int op, int x, int val) { switch (op) { case OP_EQUAL: return x == val; case OP_BIGGER: return x > val; case OP_SMALLER: return x < val; default: return true; } } In this simple example, obviously yes. Now imagine you have 1000 operators. would it still be faster than a class hierarchy? Is there a threshold when a class hierarchy becomes more efficient in speed than a switch statement? (in memory obviously not) abstract class Op { abstract public boolean accept(int x, int val); } And then one class per operator.

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  • Arrow operator (->) usage in C

    - by Mohit Deshpande
    I am currently learning C by reading a good beginner's book called "Teach Yourself C in 21 Days" (I have already learned Java and C# so I am moving at a much faster pace). I was reading the chapter on pointers and the - (arrow) operator came up without explanation. I think that it is used to call members and functions (like the equivalent of the . (dot) operator, but for pointers instead of members). But I am not entirely sure. Could I please get an explanation and a code sample?

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  • subclassing QList and operator+ overloading

    - by Milen
    I would like to be able to add two QList objects. For example: QList<int> b; b.append(10); b.append(20); b.append(30); QList<int> c; c.append(1); c.append(2); c.append(3); QList<int> d; d = b + c; For this reason, I decided to subclass the QList and to overload the operator+. Here is my code: class List : public QList<int> { public: List() : QList<int>() {} // Add QList + QList friend List operator+(const List& a1, const List& a2); }; List operator+(const List& a1, const List& a2) { List myList; myList.append(a1[0] + a2[0]); myList.append(a1[1] + a2[1]); myList.append(a1[2] + a2[2]); return myList; } int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); List b; b.append(10); b.append(20); b.append(30); List c; c.append(1); c.append(2); c.append(3); List d; d = b + c; List::iterator i; for(i = d.begin(); i != d.end(); ++i) qDebug() << *i; return a.exec(); } , the result is correct but I am not sure whether this is a good approach. I would like to ask whether there is better solution?

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  • friendship and operator overloading help

    - by sil3nt
    hello there, I have the following class #ifndef Container_H #define Container_H #include <iostream> using namespace std; class Container{ friend bool operator==(const Container &rhs,const Container &lhs); public: void display(ostream & out) const; private: int sizeC; // size of Container int capacityC; // capacity of dynamic array int * elements; // pntr to dynamic array }; ostream & operator<< (ostream & out, const Container & aCont); #endif and this source file #include "container.h" /*----------------------------********************************************* note: to test whether capacityC and sizeC are equal, must i add 1 to sizeC? seeing as sizeC starts off with 0?? */ Container::Container(int maxCapacity){ capacityC = maxCapacity; elements = new int [capacityC]; sizeC = 0; } Container::~Container(){ delete [] elements; } Container::Container(const Container & origCont){ //copy constructor? int i = 0; for (i = 0; i<capacityC; i++){ //capacity to be used here? (*this).elements[i] = origCont.elements[i]; } } bool Container::empty() const{ if (sizeC == 0){ return true; }else{ return false; } } void Container::insert(int item, int index){ if ( sizeC == capacityC ){ cout << "\n*** Next: Bye!\n"; return; // ? have return here? } if ( (index >= 0) && (index <= capacityC) ){ elements[index] = item; sizeC++; } if ( (index < 0) && (index > capacityC) ){ cout<<"*** Illegal location to insert--"<< index << ". Container unchanged. ***\n"; }//error here not valid? according to original a3? have i implemented wrong? } void Container::erase(int index){ if ( (index >= 0) && (index <= capacityC) ){ //correct here? legal location? int i = 0; while (i<capacityC){ //correct? elements[index] = elements[index+1]; //check if index increases here. i++; } sizeC=sizeC-1; //correct? updated sizeC? }else{ cout<<"*** Illegal location to be removed--"<< index << ". Container unchanged. ***\n"; } } int Container::size()const{ return sizeC; //correct? } /* bool Container::operator==(const Container &rhs,const Container &lhs){ int equal = 0, i = 0; for (i = 0; i < capacityC ; i++){ if ( rhs.elements[i] == lhs.elements[i] ){ equal++; } } if (equal == sizeC){ return true; }else{ return false; } } ostream & operator<< (ostream & out, const Container & aCont){ int i = 0; for (i = 0; i<sizeC; i++){ out<< aCont.elements[i] << " " << endl; } } */ I dont have the other functions in the header file (just a quikie). Anyways, the last two functions in "/* */" I cant get to work, what am I doing wrong here? the first function is to see whether the two arrays are equal to one another

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