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  • Operator & and * at function prototype in class

    - by Puyover
    I'm having a problem with a class like this: class Sprite { ... bool checkCollision(Sprite &spr); ... }; So, if I have that class, I can do this: ball.checkCollision(bar1); But if I change the class to this: class Sprite { ... bool checkCollision(Sprite* spr); ... }; I have to do this: ball.checkCollision(&bar1); So, what's the difference?? It's better a way instead other? Thank you.

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  • Java print binary number using bit-wise operator

    - by user69514
    Hi I am creating a method that will take a number and print it along with its binary representation. The problems is that my method prints all 0's for any positive number, and all 1's for any negative number private static void display( int number ){ System.out.print(number + "\t"); int mask = 1 << 31; for(int i=1; i<=32; i++) { if( (mask & number) != 0 ) System.out.print(1); else System.out.print(0); if( (i % 4) == 0 ) System.out.print(" "); } }

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  • Assignment in conditional operator

    - by DuoSRX
    I've seen a lot this kind of code recently : if ($foo = $bar->getFoo()) { baz($foo); } Is this considered good or bad practice ? For example, Netbeans IDE give a notice if you use this kind of code : Possible accidental assignment, assignments in conditions should be avoided What do you think ?

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  • Is tertiary operator possible here?

    - by silow
    I'm trying to set $value1, $value2, $value3 entirely using tertiary operators. This is what it looks like without tertiary if ($chk1 == 20) { $value1 = true; if ($chk2 == 40) { $value2 = 100 ; $value3 = 300; } else { $value2 = 200 ; $value3 = 400; } } else { $value1 = false; } I can set $value2 and $value3, but not sure how to set $value1. Can it be done? if ($chk1 == 20) { $value1 = true; $value2 = ($chk2 == 40) ? 100 : 200; $value3 = ($chk2 == 40) ? 300 : 400; } else { $value1 = false; }

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  • C++ operator[ ] on integer litteral

    - by gregseth
    I found this piece of code: char a = 1["ABC"]; A few quick test led me to the fact it was the same than writing: char a = "ABC"[1]; Which seems far more logical to me. So my questions: Why is this notation valid? Is there any reason to write something that way?

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  • Optimizing MySQL queries with IN operator

    - by Arkadiusz Kondas
    I have a MySQL database with a fairly large table where the products are. Each of them has its own id and categoryId field where there is a category id belongs to this product. Now I have a query that pulls out products from given categories such as: SELECT * FROM products WHERE categoryId IN ( 1, 2, 3, 4, 5, 34, 6, 7, 8, 9, 10, 11, 12 ) Of course, come a WHERE clause and ORDER BY sort but not in this thing. Let's say that these products is 250k and the visits are over 100k per day. Under such conditions in the table slow_log registered weight of these queries with large generation time. Do you have any ideas how to optimize the given problem? Table engine is MyISAM.

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  • Operator & and * at function prototipe in class

    - by Puyover
    I'm having a problem with a class like this: class Sprite { ... bool checkCollision(Sprite &spr); ... }; So, if I have that clase, I can do this: ball.checkCollision(bar1); But if I change the class to this: class Sprite { ... bool checkCollision(Sprite* spr); ... }; I have to do this: ball.checkCollision(&bar1); So, what's the difference?? It's better a way instead other? Thank you.

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  • Changing the values of a class returned by the array [] operator

    - by devdept
    The question is: at the end of this code the value of ptArray[0].X is 3.33 or 1.11? Thanks. class MyPoint { public double X, Y; public MyPoint(double x, double y) { X = x; Y = y; } } MyPoint[] ptArray = new MyPoint[2]; ptArray[0] = new MyPoint(1.11, 2.22); MyPoint first = ptArray[0]; // Am I changing ptArray[0] here or not? first.X = 3.33; first.Y = 4.44;

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  • PHP String to Float

    - by John
    I am not familiar with PHP at all and had a quick question. I have 2 variables @pricePerUnit and @invoicedUnits. Here's the code that is setting these to values: $InvoicedUnits = ((string) $InvoiceLineItem->InvoicedUnits); $pricePerUnit = ((string) $InvoiceLineItem->PricePerUnit); If I output this, I get the correct values. Lets say 5000 invoiced units and 1.00 for price. Now, I need to show the total amount spent. When I multiply these two together it doesn't work (as expected, these are strings). But I have no clue how to parse/cast/convert variables in PHP. What should I do?

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  • <hash_set> equality operator doesn't work in VS2010

    - by ProgramWriter
    Sample code: std::hash_set<int> hs1; // also i try std::unorded_set<int> - same effect std::hash_set<int> hs2; hs1.insert(15); hs1.insert(20); hs2.insert(20); hs2.insert(15); assert(hs1 == hs2); hash_set doesn't stores elements in some order defined by hash function... why? Please note that this code works in VS2008 using stdext::hash_set.

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  • Overloading the QDataStream << and >> operators for a user-defined type

    - by Alex Wood
    I have a an object I'd like to be able to read and write to/from a QDataStream. The header is as follows: class Compound { public: Compound(QString, QPixmap*, Ui::MainWindow*); void saveCurrentInfo(); void restoreSavedInfo(QGraphicsScene*); void setImage(QPixmap*); QString getName(); private: QString name, homeNotes, addNotes, expText; Ui::MainWindow *gui; QPixmap *image; struct NMRdata { QString hnmrText, cnmrText, hn_nmrText, hn_nmrNucl, notes; int hnmrFreqIndex, cnmrFreqIndex, hn_nmrFreqIndex, hnmrSolvIndex, cnmrSolvIndex, hn_nmrSolvIndex; }*nmr_data; struct IRdata { QString uvConc, lowResMethod, irText, uvText, lowResText, highResText, highResCalc, highResFnd, highResFrmla, notes; int irSolvIndex, uvSolvIndex; }*ir_data; struct PhysicalData { QString mpEdit, bpEdit, mpParensEdit, bpParensEdit, rfEdit, phyText, optAlpha, optConc, elemText, elemFrmla, notes; int phySolvIndex, optSolvIndex; }*physical_data; }; For all intensive purposes, the class just serves as an abstraction for a handful of QStrings and a QPixmap. Ideally, I would be able to write a QList to a QDataStream but I'm not exactly sure how to go about doing this. If operator overloading is a suitable solution, would writing code like friend QDataStream& operator << (QDataStream&,Compound) { ... } be a potential solution? I'm very open to suggestions! Please let me know if any further clarification is needed.

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  • Reference-type conversion operators: asking for trouble?

    - by Ben
    When I compile the following code using g++ class A {}; void foo(A&) {} int main() { foo(A()); return 0; } I get the following error messages: > g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:10: error: invalid initialization of non-const reference of type ‘A&’ from a temporary of type ‘A’ test.cpp:6: error: in passing argument 1 of ‘void foo(A&)’ After some reflection, these errors make plenty of sense to me. A() is just a temporary value, not an assignable location on the stack, so it wouldn't seem to have an address. If it doesn't have an address, then I can't hold a reference to it. Okay, fine. But wait! If I add the following conversion operator to the class A class A { public: operator A&() { return *this; } }; then all is well! My question is whether this even remotely safe. What exactly does this point to when A() is constructed as a temporary value? I am given some confidence by the fact that void foo(const A&) {} can accept temporary values according to g++ and all other compilers I've used. The const keyword can always be cast away, so it would surprise me if there were any actual semantic differences between a const A& parameter and an A& parameter. So I guess that's another way of asking my question: why is a const reference to a temporary value considered safe by the compiler whereas a non-const reference is not?

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  • Declaring functors for comparison ??

    - by Mr.Gando
    Hello, I have seen other people questions but found none that applied to what I'm trying to achieve here. I'm trying to sort Entities via my EntityManager class using std::sort and a std::vector<Entity *> /*Entity.h*/ class Entity { public: float x,y; }; struct compareByX{ bool operator()(const GameEntity &a, const GameEntity &b) { return (a.x < b.x); } }; /*Class EntityManager that uses Entitiy*/ typedef std::vector<Entity *> ENTITY_VECTOR; //Entity reference vector class EntityManager: public Entity { private: ENTITY_VECTOR managedEntities; public: void sortEntitiesX(); }; void EntityManager::sortEntitiesX() { /*perform sorting of the entitiesList by their X value*/ compareByX comparer; std::sort(entityList.begin(), entityList.end(), comparer); } I'm getting a dozen of errors like : error: no match for call to '(compareByX) (GameEntity* const&, GameEntity* const&)' : note: candidates are: bool compareByX::operator()(const GameEntity&, const GameEntity&) I'm not sure but ENTITY_VECTOR is std::vector<Entity *> , and I don't know if that could be the problem when using the compareByX functor ? I'm pretty new to C++, so any kind of help is welcome.

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  • Understanding evaluation of expressions containing '++' and '->' operators in C.

    - by Leif Ericson
    Consider this example: struct { int num; } s, *ps; s.num = 0; ps = &s; ++ps->num; printf("%d", s.num); /* Prints 1 */ It prints 1. So I understand that it is because according to operators precedence, -> is higher than ++, so the value ps->num (which is 0) is firstly fetched and then the ++ operator operates on it, so it increments it to 1. struct { int num; } s, *ps; s.num = 0; ps = &s; ps++->num; printf("%d", s.num); /* Prints 0 */ In this example I get 0 and I don't understand why; the explanation of the first example should be the same for this example. But it seems that this expression is evaluated as follows: At first, the operator ++ operates, and it operates on ps, so it increments it to the next struct. Only then -> operates and it does nothing because it just fetches the num field of the next struct and does nothing with it. But it contradicts the precedence of operators, which says that -> have higher precedence than ++. Can someone explain this behavior? Edit: After reading two answers which refer to a C++ precedence tables which indicate that a prefix ++/-- operators have lower precedence than ->, I did some googling and came up with this link that states that this rule applies also to C itself. It fits exactly and fully explains this behavior, but I must add that the table in this link contradicts a table in my own copy of K&R ANSI C. So if you have suggestions as to which source is correct I would like to know. Thanks.

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  • Swig C++ Lua Pass class by reference

    - by Jeremy
    I don't know why I'm having a hard time with this. All I want to do is this: class foo { public: foo(){} ~foo(){} float a,b; }; class foo2 { public: foo2(){} foo2(const foo &f){*this = f;} ~foo2(){} void operator=(const foo& f){ x = f.a; y = f.b; } float x,y; }; /* Usage(cpp): foo f; foo2 f2(f); //or using the = operator f2 = f; */ The problem I'm having is that, after swigging this code, I can't figure out how to make the lua script play nice. /* Usage(lua) f = example.foo() f2 = example.foo2(f) --error */ The error I get is "Wrong arguments for overloaded function 'new_Foo2'": Possible c/c++ prototypes are: foo2() foo2(foo const &) The same thing happens if I try and use do f2 = f. As I understand it everything is stored as a pointer so I did try adding an additional constructor that took a pointer to foo but to no avail.

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  • Automatically converting an A* into a B*

    - by Xavier Nodet
    Hi, Suppose I'm given a class A. I would like to wrap pointers to it into a small class B, some kind of smart pointer, with the constraint that a B* is automatically converted to an A* so that I don't need to rewrite the code that already uses A*. I would therefore want to modify B so that the following compiles... struct A { void foo() {} }; template <class K> struct B { B(K* k) : _k(k) {} //operator K*() {return _k;} //K* operator->() {return _k;} private: K* _k; }; void doSomething(A*) {} void test() { A a; A* pointer_to_a (&a); B<A> b (pointer_to_a); //b->foo(); // I don't need those two... //doSomething(b); B<A>* pointer_to_b (&b); pointer_to_b->foo(); // 'foo' : is not a member of 'B<K>' doSomething(pointer_to_b); // 'doSomething' : cannot convert parameter 1 from 'B<K> *' to 'A *' } Note that B inheriting from A is not an option (instances of A are created in factories out of my control)... Is it possible? Thanks.

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  • Is it possible to implement events in C++?

    - by acidzombie24
    I wanted to implement a C# event in C++ just to see if i could do it. I got stuck, i know the bottom is wrong but what i realize my biggest problem is... How do i overload the () operator to be whatever is in T in this case int func(float)? I cant? can i? Can i implement a good alternative? #include <deque> using namespace std; typedef int(*MyFunc)(float); template<class T> class MyEvent { deque<T> ls; public: MyEvent& operator +=(T t) { ls.push_back(t); return *this; } }; static int test(float f){return (int)f; } int main(){ MyEvent<MyFunc> e; e += test; }

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