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  • C++ overide global operator comma gives error

    - by uray
    the second function gives error C2803 http://msdn.microsoft.com/en-us/library/zy7kx46x%28VS.80%29.aspx : 'operator ,' must have at least one formal parameter of class type. any clue? template<class T,class A = std::allocator<T>> class Sequence : public std::vector<T,A> { public: Sequence<T,A>& operator,(const T& a) { this->push_back(a); return *this; } Sequence<T,A>& operator,(const Sequence<T,A>& a) { for(Sequence<T,A>::size_type i=0 ; i<a.size() ; i++) { this->push_back(a.at(i)); } return *this; } }; //this works! template<typename T> Sequence<T> operator,(const T& a, const T&b) { Sequence<T> seq; seq.push_back(a); seq.push_back(b); return seq; } //this gives error C2803! Sequence<double> operator,(const double& a, const double& b) { Sequence<double> seq; seq.push_back(a); seq.push_back(b); return seq; }

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  • what does this C++ line of code mean "sol<?=f((1<<n)-1,i,0)+abs(P[i])*price;"

    - by KItis
    Could anyone help me to understand following line of code. sol I am studying an algorithm written using c++ and it has following operator " following is the error message returned. Hello.cpp: In function ‘int main()’: Hello.cpp:115: error: ‘memset’ was not declared in this scope Hello.cpp:142: error: expected primary-expression before ‘?’ token Hello.cpp:142: error: expected primary-expression before ‘=’ token Hello.cpp:142: error: expected ‘:’ before ‘;’ token Hello.cpp:142: error: expected primary-expression before ‘;’ token may be " Thanks in advance for the time you spent reading this post.

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  • Any way to allow classes implementing IEntity and downcast to have operator == comparisons?

    - by George Mauer
    Basically here's the issue. All entities in my system are identified by their type and their id. new Customer() { Id = 1} == new Customer() {Id = 1}; new Customer() { Id = 1} != new Customer() {Id = 2}; new Customer() { Id = 1} != new Product() {Id = 1}; Pretty standard scenario. Since all Entities have an Id I define an interface for all entities. public interface IEntity { int Id { get; set;} } And to simplify creation of entities I make public abstract class BaseEntity<T> : where T : IEntity { int Id { get; set;} public static bool operator ==(BaseEntity<T> e1, BaseEntity<T> e2) { if (object.ReferenceEquals(null, e1)) return false; return e1.Equals(e2); } public static bool operator !=(BaseEntity<T> e1, BaseEntity<T> e2) { return !(e1 == e2); } } where Customer and Product are something like public class Customer : BaseEntity<Customer>, IEntity {} public class Product : BaseEntity<Product>, IEntity {} I think this is hunky dory. I think all I have to do is override Equals in each entity (if I'm super clever, I can even override it only once in the BaseEntity) and everything with work. So now I'm expanding my test coverage and find that its not quite so simple! First of all , when downcasting to IEntity and using == the BaseEntity< override is not used. So what's the solution? Is there something else I can do? If not, this is seriously annoying. Upadate It would seem that there is something wrong with my tests - or rather with comparing on generics. Check this out [Test] public void when_created_manually_non_generic() { // PASSES! var e1 = new Terminal() {Id = 1}; var e2 = new Terminal() {Id = 1}; Assert.IsTrue(e1 == e2); } [Test] public void when_created_manually_generic() { // FAILS! GenericCompare(new Terminal() { Id = 1 }, new Terminal() { Id = 1 }); } private void GenericCompare<T>(T e1, T e2) where T : class, IEntity { Assert.IsTrue(e1 == e2); } Whats going on here? This is not as big a problem as I was afraid, but is still quite annoying and a completely unintuitive way for the language to behave. Update Update Ah I get it, the generic implicitly downcasts to IEntity for some reason. I stand by this being unintuitive and potentially problematic for my Domain's consumers as they need to remember that anything happening within a generic method or class needs to be compared with Equals()

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  • Calling all the 3 functions while using or operator even after returning true as a result.

    - by Shantanu Gupta
    I am calling three functions in my code where i want to validate some of my fields. When I tries to work with the code given below. It checks only for first value until it gets false result. I want some thing like that if fisrt function returns true then it should also call next function and so on. What can be used instead of Or Operator to do this. if (IsFieldEmpty(ref txtFactoryName, true, "Required") || IsFieldEmpty(ref txtShortName, true, "Required") || IsFieldEmpty(ref cboGodown, true, "Required")) { }

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  • Why do I need an intermediate conversion to go from struct to decimal, but not struct to int?

    - by Jesse McGrew
    I have a struct like this, with an explicit conversion to float: struct TwFix32 { public static explicit operator float(TwFix32 x) { ... } } I can convert a TwFix32 to int with a single explicit cast: (int)fix32 But to convert it to decimal, I have to use two casts: (decimal)(float)fix32 There is no implicit conversion from float to either int or decimal. Why does the compiler let me omit the intermediate cast to float when I'm going to int, but not when I'm going to decimal?

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  • How does the bitwise operator '^' work?

    - by SpawnCxy
    I'm a little confused when I see the output of following code: $x = "a"; $y = "b"; $x ^= $y; $y ^= $x; $x ^= $y; echo $x; //got b echo $y; //got a And I wonder how does the operator ^ work here?Explanations with clarity would be greatly appreciated!

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  • What are the best practices for implementing the == operator for a class in C#?

    - by remio
    While implementing an == operator, I have the feeling that I am missing some essential points. Hence, I am searching some best practices around that. Here are some related questions I am thinking about: How to cleanly handle the reference comparison? Should it be implemented through a IEquatable<T>-like interface? Or overriding object.Equals? And what about the != operator? (this list might not be exhaustive).

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  • Implementing operator< in C++

    - by Vulcan Eager
    I have a class with a few numeric fields such as: class Class1 { int a; int b; int c; public: // constructor and so on... bool operator<(const Class1& other) const; }; I need to use objects of this class as a key in an std::map. I therefore implement operator<. What is the simplest implementation of operator< to use here?

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  • Operator Overloading in C++ as int + obj

    - by Azher
    Hi Guys, I have following class:- class myclass { size_t st; myclass(size_t pst) { st=pst; } operator int() { return (int)st; } int operator+(int intojb) { return int(st) + intobj; } }; this works fine as long as I use it like this:- char* src="This is test string"; int i= myclass(strlen(src)) + 100; but I am unable to do this:- int i= 100+ myclass(strlen(src)); Any idea, how can I achieve this?? Thanks in advance. Regards,

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  • C# XOR on two byte variables will not compile without a cast

    - by Ash
    Why does the following raise a compile time error: 'Cannot implicitly convert type 'int' to 'byte': byte a = 25; byte b = 60; byte c = a ^ b; This would make sense if I were using an arithmentic operator because the result of a + b could be larger than can be stored in a single byte. However applying this to the XOR operator is pointless. XOR here it a bitwise operation that can never overflow a byte. using a cast around both operands works: byte c = (byte)(a ^ b);

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  • How can I access the sign bit of a number in C++?

    - by Keand64
    I want to be able to access the sign bit of a number in C++. My current code looks something like this: int sign bit = number >> 31; That appears to work, giving me 0 for positive numbers and -1 for negative numbers. However, I don't see how I get -1 for negative numbers: if 12 is 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 1100 then -12 is 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 0011 and shifting it 31 bits would make 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0001 which is 1, not -1, so why do I get -1 when I shift it?

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  • Performance difference in for loop condition?

    - by CSharperWithJava
    Hello all, I have a simple question that I am posing mostly for my curiousity. What are the differences between these two lines of code? (in C++) for(int i = 0; i < N, N > 0; i++) for(int i = 0; i < N && N > 0; i++) The selection of the conditions is completely arbitrary, I'm just interested in the differences between , and &&. I'm not a beginner to coding by any means, but I've never bothered with the comma operator. Are there performance/behavior differences or is it purely aesthetic? One last note, I know there are bigger performance fish to fry than a conditional operator, but I'm just curious. Indulge me. Edit Thanks for your answers. It turns out the code that prompted this question had misused the comma operator in the way I've described. I wondered what the difference was and why it wasn't a && operator, but it was just written incorrectly. I didn't think anything was wrong with it because it worked just fine. Thanks for straightening me out.

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  • How to make += operator keep the object reference?

    - by orloffm
    Say, I have a class: class M { public int val; And also a + operator inside it: public static M operator +(M a, M b) { M c = new M(); c.val = a.val + b.val; return c; } } And I've got a List of the objects of the class: List<M> ms = new List(); M obj = new M(); obj.val = 5; ms.Add(obj); Some other object: M addie = new M(); addie.val = 3; I can do this: ms[0] += addie; and it surely works as I expect - the value in the list is changed. But if I want to do M fromList = ms[0]; fromList += addie; it doesn't change the value in ms for obvious reasons. But intuitively I expect ms[0] to also change after that. Really, I pick the object from the list and then I increase it's value with some other object. So, since I held a reference to ms[0] in fromList before addition, I want still to hold it in fromList after performing it. Are there any ways to achieve that?

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  • Operator Overloading in C

    - by Leif Andersen
    In C++, I can change the operator on a specific class by doing something like this: MyClass::operator==/*Or some other operator such as =, >, etc.*/(Const MyClass rhs) { /* Do Stuff*/; } But with there being no classes (built in by default) in C. So, how could I do operator overloading for just general functions? For example, if I remember correctly, importing stdlib.h gives you the - operator, which is just syntactic sugar for (*strcut_name).struct_element. So how can I do this in C? Thank you.

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  • Please explain this php expression "!$variable"

    - by DogBot
    What does an exclamaton mark in front of a variable mean? And how is it being used in this piece of code? EDIT: From the answers so far I suspect that I also should mention that this code is in a function where one of the parameters is $mytype ....would this be a way of checking if $mytype was passed? - Thanks to all of the responders so far. $myclass = null; if ($mytype == null && ($PAGE->pagetype <> 'site-index' && $PAGE->pagetype <>'admin-index')) { return $myclass; } elseif ($mytype == null && ($PAGE->pagetype == 'site-index' || $PAGE->pagetype =='admin-index')) { $myclass = ' active_tree_node'; return $myclass; } elseif (!$mytype == null && ($PAGE->pagetype == 'site-index' || $PAGE->pagetype =='admin-index')) { return $myclass; }`

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  • C# implicit conversions and == operator

    - by Arnis L.
    Some code for context: class a { } class b { public a a{get;set;} public static implicit operator a(b b) { return b.a; } } a a=null; b b=null; a = b; //compiler: cannot apply operator '==' to operands of type tralala... bool c = a == b; Is it possible to use == operator on different type instances, where one can implicitly convert to another? What did i miss? Edit: If types must be the same calling ==, then why int a=1; double b=1; bool c=a==b; works?

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  • Algorithm for bitwise fiddling

    - by EquinoX
    If I have a 32-bit binary number and I want to replace the lower 16-bit of the binary number with a 16-bit number that I have and keep the upper 16-bit of that number to produce a new binary number.. how can I do this using simple bitwise operator? For example the 32-bit binary number is: 1010 0000 1011 1111 0100 1000 1010 1001 and the lower 16-bit I have is: 0000 0000 0000 0001 so the result is: 1010 0000 1011 1111 0000 0000 0000 0001 how can I do this?

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  • undefined C/C++ symbol as operator

    - by uray
    I notice that the character/symbol '`' and '@' is not used as an operator in C/C++, does anyone know the reason or historically why its so? if its really not used, is it safe to define those symbols as another operator/statement using #define?

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  • How to change the meaning of pointer access operator

    - by kumar_m_kiran
    Hi All, This may be very obvious question, pardon me if so. I have below code snippet out of my project, #include <stdio.h> class X { public: int i; X() : i(0) {}; }; int main(int argc,char *arv[]) { X *ptr = new X[10]; unsigned index = 5; cout<<ptr[index].i<<endl; return 0; } Question Can I change the meaning of the ptr[index] ? Because I need to return the value of ptr[a[index]] where a is an array for subindexing. I do not want to modify existing source code. Any new function added which can change the behavior is needed. Since the access to index operator is in too many places (536 to be precise) in my code, and has complex formulas inside the index subscript operator, I am not inclined to change the code in many locations. PS : 1. I tried operator overload and came to conclusion that it is not possible. 2. Also p[i] will be transformed into *(p+i). I cannot redefine the basic operator '+'. So just want to reconfirm my understanding and if there are any possible short-cuts to achieve. Else I need fix it by royal method of changing every line of code :) .

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  • Is there an exponent operator in C#?

    - by Charlie
    For example, does an operator exist to handle this? float Result, Number1, Number2; Number1 = 2; Number2 = 2; Result = Number1 (operator) Number2; In the past the ^ operator has served as an exponential operator in other languages, but in C# it is a bit-wise operator. Do I have to write a loop or include another namespace to handle exponential operations? If so, how do I handle exponential operations using non-integers?

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  • What is the safest way to subtract two System.Runtime.InteropServices.ComTypes.FILETIME objects

    - by Anindya Chatterjee
    I wonder what is the safest way to subtract two System.Runtime.InteropServices.ComTypes.FILETIME objects? I used the following code but sometimes it gives me ArithmaticOverflow exception due to the negative number in Low 32-bit values. I am not sure enclosing the body with unchecked will serve the purpose or not. Please give me some suggestion on how to do it safely without getting any runtime exception or CS0675 warning message. private static UInt64 SubtractTimes(FILETIME a, FILETIME b) { UInt64 aInt = ((UInt64)(a.dwHighDateTime << 32)) | (UInt32)a.dwLowDateTime; UInt64 bInt = ((UInt64)(b.dwHighDateTime << 32)) | (UInt32)b.dwLowDateTime; return aInt - bInt; }

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